Two primes on dual format cameras (24/1.4 and 85/1.4 on D700 and D300)

Discussion in 'Nikon' started by hocus_focus, Jul 1, 2011.

  1. I came up with the following idea: mounting 24/1.4 and 85/1.4 on dual format cameras, let's say on d700 and d300.
    In terms of field of view and depth of field, this gives effectively 24/1.4, 35/2.2, 85/1.4 and 135/2.2. I would consider this set for portraits on location, weddings, baby shoots and travel.
    If anyone uses that lens set with dual format cameras, I'd love to hear their opinion because I have some concerns.
    1. First, while 135/2.2 is still impressive for portraits and sports, the exotic 24/1.4 becomes a boring 35/2.2 on crop camera.


    2. Second, I'm concerned if the added noise will degrade your expensive lens collection.


    3. Third, I wonder if you don't get tangled up with the lens changes and their different properties on dual format cameras.

      At any point in time, you will either have 35/2.2 and 85/1.4 or 24/1.4 and 135/2.2 (in terms of FoV and DoF).
      Is this feasible in practice?
     
  2. Why are you indicating a different f-stop for the lenses on a crop camera?
     
  3. Why are you indicating a different f-stop for the lenses on a crop camera?​
    Because a smaller sensor produces more depth of field. It's called equivalence. You can calculate the difference here.
    In other terms, 24/1.4 on d300 will not produce the same images as 35/1.4 on d700 given the same distance and FoV.
    24/1.4 on d300 will look more like 35/2.2 on d700, excluding noise and detail.
     
  4. I don't see why it should be confusing - my Nikkors are all full frame, but I've switched between a crop-sensor Canon and a film camera without any difficulty; you could roughly achieve this with one camera if you got a (third party) 1.4x teleconverter, after all - or force the camera into DX mode (or just crop the result yourself). There are more differences between the optical characteristics of the native lenses at these focal lengths than just the aperture, for what it's worth. It may be a sensible way of picking your lens selection if you already have both bodies, but I'm not sure I'd go that way from scratch. I'm not sure I understand your point about noise, by the way.
     
  5. I'm not sure I understand your point about noise, by the way.​
    Full frame cameras generally produce less noise and more detail. I'm concerned about losing detail and adding noise when screwing prime lenses on a crop camera.
     
  6. Oh, right ... maybe I should read more carefully.
    I've never thought of doing something like that, I have a D700 and a D200 so I guess it could be done, but I don't think it would make much difference. I'd be more likely to use the D700 and just stop down and/or move closer to the subject if I was looking for changing the DOF or wanting different framing. You shouldn't get any degradation from noise if you don't try to use a higher ISO than the camera will produce good images with when properly exposed.
     
  7. I'd be more likely to use the D700 and just stop down and/or move closer to the subject if I was looking for changing the DOF or wanting different framing.​
    The thing is: I do not want to have more depth of field. I pick f/1.4 lenses to achieve shallow DoF. However, on crop cameras, part of that shallow DoF is lost.
    Moving in closer is not always an option but is a good idea nonetheless :)
     
  8. Spearhead

    Spearhead Moderator

    boring 35/2.2 on crop camera.​
    Lenses aren't boring. Photographs can be boring, photographers can be boring, but a lens is just a tool. This guy shoots almost exclusively with a 35 on a full frame camera.
     
  9. Lenses aren't boring. Photographs can be boring, photographers can be boring, but a lens is just a tool. This guy shoots almost exclusively with a 35 on a full frame camera.​
    Well good for him! That was such a bland, boring remark... sigh.
     
  10. You're just confusing yourself by pretending that the aperture is "effectively" different between sensor formats. The most important effect of the aperture is that it balances against shutter speed to get you the right exposure. This doesn't change at all when you switch between FX and DX camera bodies.
    Really, all the stuff you hear about a lens being "effectively" something different on a DX body is nonsense that causes lots of misunderstanding among people who don't actually understand how cameras and lenses really work. Ultimately, you cannot take "exactly the same picture" with cameras of different formats. You can try to adjust various parameters to get close, but you can never really get it exactly.
     
  11. So every time you need to change a lens you actually have to change TWO lenses (unless you're leaving the body cap on a body)
    For me this would get frustrating but why not just try it. Everyone has different ways of working.
     
  12. Full frame cameras generally produce less noise and more detail. I'm concerned about losing detail and adding noise when screwing prime lenses on a crop camera.​
    Ah, I wondered. Full frame cameras tend to produce less noise at the same relative aperture as a crop sensor camera (mostly) because, at the same pixel count, more light hits each sensor site. At f/2, the amount of light per unit area doesn't depend on focal length, but a D300's pixels are (1.5x1.5=)2.25x smaller than a D700's. The actual difference is slightly more in favour of the larger sensor, partly because a fixed amount of the sensor area has to be occupied with logic and data transfer, but within a sensor generation it's the pixel size that matters.

    If you consider an 85mm f/1.4 on a DX camera to equate to a 127.5mm f/2.1 lens on FX, bear in mind that a native 127mm f/2.1 lens lets in less light by a factor of 2.25, which balances out the noise issue (mostly, as I said). Hence you could say that an 85mm f/1.4 on a DX body at ISO 200 is like a 127.5mm f/2.1 lens on an FX body at ISO 500, in terms of field of view, exposure and depth of field. But that might just confuse people who prefer to think in terms of a focal length being a focal length and an ISO setting being an ISO setting. (You can get into the same arguments about teleconverters, cropping images, and film grain. And I have, and I don't want to again!)

    In summary: don't worry about noise, to a decent approximation the noise behaviour of a D300 with an 85mm f/1.4 lens and a D700 with a 135mm f/2 lens, both used wide open, will be similar. It is, however, easier to make a lens that behaves well optically at f/2 than at f/1.4, so you might be right to have concerns about resolution, especially away from f/8-ish.
     
  13. Craig's response is exactly the way previous threads on this subject have gone - "you're confused by thinking in the way that exactly explains the relationship between depth of field, focal length and sensor size; you should think of it in my terms instead, and then you'll see that it makes absolutely no sense!" - and I recommend that you agree to differ. I suspect that some people whose expertise I greatly value might be refusing to read any of my posts after similar disagreements...

    Craig - I don't mean to be disrespectful or antagonistic, I'm just explaining how your post sounds from the perspective of those who believe that the geometry of the situation explains the "equivalence" perfectly. I'm happy to be told there's a flaw in the reasoning of this principle, but I've been in very long threads in which no specific problem with it has been stated, other than that it's another way of thinking about the situation. What you can't do is explain the depth of field change by stating a different focal length - which nobody seems to mind discussing - and relative aperture, and then ignore both sensitivity and shutter speed. Treat everything together, and it makes sense, with the understanding that the existing concepts of "focal length", "aperture" and "ISO" are equally valid and have their uses.

    And I wasn't going to get involved again... *sigh*.
     
  14. Actually I shoot events with a pair of D700/D300 and my preffered lens setup is based on this:
    Nikon 24/1.4
    Sigma 85/1.4
    Nikon 180/2.8
    Sometimes I may bring another lens if I know I have particular needs but for most the three lenses are my workhorses.
    I have no problem switching lenses to get the appropriate FOV I need. The only observation I have: Sigma 85/1.4 and Nikon 18/2.8 are shinning on both cameras. Nikon 24/1.4 is really my best lens on D700... but on D300 it seems that does not show so much magic... I do not know if this is because of my lens, because of my D300 or because of my style of shooting... :)
     
  15. You're just confusing yourself by pretending that the aperture is "effectively" different between sensor formats. The most important effect of the aperture is that it balances against shutter speed to get you the right exposure. This doesn't change at all when you switch between FX and DX camera bodies.​
    I'm not talking about exposure but about depth of field. Major difference!
    So every time you need to change a lens you actually have to change TWO lenses (unless you're leaving the body cap on a body)​
    Good point but even with one body and two lenses, you still need to grab two lenses. Where else do you put your unscrewed lens? In a lens case or on a body... doesn't change a thing. Except that if you screw it on a body, you don't need the cap!
     
  16. ShunCheung

    ShunCheung Administrator

    I came up with the following idea: mounting 24/1.4 and 85/1.4 on dual format cameras, let's say on d700 and d300.
    In terms of field of view and depth of field, this gives effectively 24/1.4, 35/2.2, 85/1.4 and 135/2.2. I would consider this set for portraits on location, weddings, baby shoots and travel.​
    Very interesting. Merely two days ago, the OP was telling people that he was using two Canon lenses, a 24-70mm/f2.8 and a 24-105mm/f4 on a 5D Mark II for weddings: 24-70/2.8 vs 24-105/4 IS at wedding.
    To me, obviously the 85mm/f1.4 is good for portraits. Otherwise, it makes little sense to use a 24mm/f1.4 and a 85mm/f1.4 for weddings, baby shoots and travel. The OP's existing Canon lenses make far more sense for wedding photography.
     
  17. Just my personal opinion, but I have always found a 35mm and 85mm lens combination to be extremely versatile on a film or FX body. A little wide and a little long covers a lot of shooting situations.
     
  18. It seems to me a pretty theoretical approach in photography; it sounds feasible.
    But in the real life, (-or at least in my shooting life-), I don`t see the point of using -only- (superexpensive) primes that are forced to be used in two inseparable bodies/formats. They are actually nice, but maybe not as practical in the field.
    I think I`d feel more confortable (portraits, wedding, baby shoots and travel) with my D700 + 24-120/4 than with four primes and two bodies.
    ... Or with two FX bodies, and two lenses (24-70 + 70-200) for weddings,
    ... or with one DX or FX body and a 85VR or 105VR for baby shoots,
    ... or with one DX or FX body with a prime for portraits,
    ... or with a DX or FX camera with a 16-85 or 24-120/4 for travel.
     
  19. I'm not talking about exposure but about depth of field. Major difference!​
    The problem is that aperture relates to both. When people make overly-generalized, technically-wrong statements like "24mm f/1.4 on FX is effectively 35mm f/2.2 on DX", it confuses people who don't understand enough about the technology to understand that you mean something much more limited than you seem to be saying. If a newbie has learned that a smaller aperture lets in less light and requires a longer exposure, he may think, based on a statement like yours, that a lens set to f/1.4 on a DX camera requires an extra stop or so of exposure time to compensate for the fact that it is "effectively" f/2.2 -- which, of course, is not true.
    A 24mm f/1.4 lens is always a 24mm f/1.4 lens. It doesn't matter what camera you put it on. A smaller sensor uses a smaller portion of the image circle, resulting in tighter framing; that's the only real difference. DOF is not, in fact, any different at all. What makes it seem different is one of three things:
    1) You compensate for the narrower angle of view by using a shorter focal length, which increases DOF;
    2) You compensate for the narrower angle of view by moving the camera farther away from the subject, which increases DOF;
    3) You calculate DOF on DX using a smaller CoC value, which reduces DOF.
    In this post, I think you're doing #3 (because that's what the dofmaster calculator does when you switch from FX to DX), and then you're narrowing the aperture to compensate for the smaller CoC value. This is how you end up claiming that f/1.4 is "effectively" f/2.2 on DX.
    My next question for you is whether you understand why the dofmaster calculator is using a different CoC for a DX camera, and how the CoC value relates to assumptions about how the image will be used. It's really not as absolute as you seem to think.
     
  20. @Craig -
    Your last post is actually the most confusing post I've seen since I don't understand your #3. Your wording doesn't make sense to me and is very baffling.
    Andrew and I have had very lengthy conversations, both in forums and through email, on how sensor size effects DOF and it boils down to this:
    The single biggest benefit of an FX/Full Frame sensor is it's behavior when using large aperture lenses. More specifically (referring to the Nikon AF System), 50mm -135mm lenses shooting with an f-stop of f/1.4 - f/4. The larger sensor produces a depth of field roughly 1.5x smaller than an equivalent focal length (75mm on FX/50mm on DX) on a 1.5x crop sensor.
    This is a tough concept to follow since DOF is not a measurable, tangible entity. It is up to one's individual perception of DOF that makes the case. It is less noticeable with smaller apertures, wider focal lengths, and at longer shooting distances from the subject. Portrait photography is where this difference is most noticeable due to the specific conditions that are related to the subject.

    I hope this brings the DOF quibble to an end...
    @ Shun --
    I also find it interesting that Hocus Focus is using a 5DMkII, D700, and D300... The only reason I can fathom is that the OP was second shooting for a pro that lent out a 5DMkII and lenses. Any light shed on this would be helpful.
    RS
     
  21. Richard: DOF is a mathematical entity and it can be calculated very precisely, but only within the context of certain assumptions. To really understand DOF conceptually, you have to understand what variables are involved.
    Here is a thought experiment: In a controlled studio environment, with a stationary tripod, shoot a scene using the same 24mm f/1.4 lens at f/1.4 using both FX and DX cameras. Print the resulting images at, say, 20x the size of the sensor. Then crop the FX print to match the narrower framing of the DX print. How do the two resulting prints differ?
     
  22. No discussion of depth of field is meaningful without a definition of the acceptable circle of confusion, but, on balance, I'd say...
    I'd say it's time to stop feeding the troll.
     
  23. I have to agree that I'd rather stick to one camera, but I can imagine that a D300 as a back-up for a D700 makes some sense, and in the scenario of already having the cameras, a couple of expensive primes might trump four of them. I'd be really sure you want the primes, though - a fast zoom does sound like a better solution for the stated scenarios unless you really want a shallow DoF.

    Craig: I agree, it's entirely possible to be confused about this if you think about it in terms of the ISO (sensitivity to light per unit area) and the aperture actually changing. However, it's also completely valid to ignore that part of the calculation, and - if someone's going to claim that "a 24mm lens used on a DX camera is equivalent to a 35mm lens on an FX camera" and "DX cameras have less depth of field" - also discuss exactly what happens to the depth of field if you think of the lens on the DX camera in terms of a lens used on FX. If you think of this scenario in terms of the "virtual FX lens" having a smaller aperture, as you say, you have to think of the sensitivity changing to explain the lack of difference in exposure time; stated in terms of ISO this makes no sense, but thought of in terms of light per sensor pixel if does make sense; you just have to accept that the amplification setting that the camera reports as its ISO value is not the quantity that you should be thinking about.

    However, the ways in which a newbie might be confused by the "equivalence" statement does not make it invalid - it just means that we need to know what we're referring to, and compensate for everything.

    Generally, when we talk about equivalent lenses for different sensor sizes, we assume that the lens is in the same place (I get to the limits of my optics here, but I'm going to suggest that the entrance pupil needs to be in the same place) and that we're trying to replicate the same field of view - that is, we're trying to take indistinguishable pictures with two different formats. If we move the camera, the perspective changes; if we use a different (equivalent) focal length, the cropping changes. If we talk about the effect of a change in focal length on depth of field, we do need to consider whether we've already moved things, but in the context of a changed sensor size and the premise that we already have an "equivalent focal length", I think it's clear what we mean.

    And we're talking in terms of a generalised lens, not any particular lens that may have focus breathing or other concerns. Strictly, the distance to the subject has an effect on the effective focal length of the lens, because the back focus distance changes, but this isn't so significant at normal distances. If it affects anything, it's the "effective focal length", not the aperture.

    I strongly disapprove of anyone plugging numbers into an on-line depth of field calculator and trying to extrapolate from the result - the magic in the box isn't that complicated. (Not to suggest that Craig does this, I just don't think it's the right way to learn about what's going on - although it's a useful tool for specific cases. I've seen a lot of DoF discussions which claim "DoFmaster says..." without further explanation.) It's much less confusing to think of the geometry of the real world. If we first set up two lenses so that two cameras with different sensor formats have exactly the same field of view (by scaling the focal length of the lens by the difference in sensor size), and we eventually intend to produce prints of the same total size from each, the depth of field is solely determined by the size and position of the entrance aperture: there's a cone of confusion passing from the entrance aperture through every point in the focal plane in the scene. What goes on behind the lens has no effect on this - to get the same depth of field (and size of background blur) it's the entrance aperture size that matters.

    F-stop is focal length divided by aperture. Increase the focal length by a factor of "x" and you need to reduce the f-stop by the same factor to keep the entrance aperture the same. Lens in the same place, same cones of confusion, same field of view, same magnification, same image.

    I would hope that DoFmaster scales the CoC down by the crop factor in the assumption that you're enlarging the result by a corresponding amount, because it talks in terms of the CoC at the sensor - this lines up with the reduced aperture that we're talking about for a larger sensor (since CoC at the same distance from the focal place scales with aperture). Generally speaking I hate talking about depth of field anyway, because it depends so much on how much you're magnifying the final image. However, that doesn't invalidate looking at the relative effect of aperture on depth of field as the format changes.

    But I agree that this is a subject that causes a lot of confusion, and that we should be careful to state our premises, and to warn novices to learn the "conventional" way of thinking about a camera first. (That said, I'm not convinced the "crop factor" is ever a useful concept for novices who don't come with a predisposed idea of the field of view of an 85mm lens...)
     
  24. there are times when dual format makes sense and times when it doesn't. some of this depends on what lenses you are using. for instance, the 24-70 and 70-200 shine on both FX and DX, but i haven't done extensive switching with primes. i tend to use the 50/1.4 only on FX, though i suppose i could use it on DX as well. but most of the time in my DX kit i'm carrying 2 zooms and only one fast prime, and i usually go for the 30/1.4.
    besides the confusion over DoF--yes, FX cameras have shallower DoF, but the aperture remains the same: 1.4 is 1.4 on both formats--it can be confusing with FF UWAs, which aren't quite so ultra on DX. it doesn't really make sense to carry DX-only lenses along with FX lenses, although something like the tokina 17/3.5 can work on both formats. really, the whole point of this is to carry less lenses, not more, and switch when you need more or less reach. if i was overly concerned about DoF and losing the "magic" of a certain lens, it would probably drive me crazy.
    it's great when you need more reach from a tele lens, but if you're shooting, say, an all-day concert and the light drops in the evening, then the high-ISO limitations of DX come into play. in that situation, i'd probably rather have a 2-body FX combo.
    i like the idea of mihai's kit, though. the only way to really know if this works for you is to try it for yourself.
    The single biggest benefit of an FX/Full Frame sensor is it's behavior when using large aperture lenses.
    well, the lower noise capabilities of FX at high ISOs are a pretty big benefit to that format, IMO.
     
  25. Generally speaking I hate talking about depth of field anyway, because it depends so much on how much you're magnifying the final image. However, that doesn't invalidate looking at the relative effect of aperture on depth of field as the format changes.​
    And I didn't get that written in time before the last few posts. :) DoF is a highly controversial subject, but whatever assumptions you make about the absolute value, you make the same assumptions in both cases; the relative effect of two sets of sensor formats/focal lengths/apertures is fixed, because all the assumptions cancel out.

    Craig: Apologies for getting at you. Remembering that the original poster is deliberately using two sensors sizes to get two different fields of view, I hope we can ignore the "produce images scaled according to the relative sensor size" scenario (but if we did, you're be right that the DoF of a 24mm lens at f/1.4 is the same on both cameras). Put another way, an f/1.4 lens is an f/1.4 lens on any format, and a 24mm lens is a 24mm lens on any format; just because we might say it "behaves like an f/2.1 lens" - and equally that it "behaves like a 35mm lens" - on another format doesn't mean that it is either of those things, we're just asking what completely different lens we might choose to use on a completely different camera (with completely different ISO - or shutter speed - settings) to get an image that appears identical, when the whole sensor is used. You can say exactly the same thing about crops from an existing sensor, or the result of bolting a teleconverter onto a lens. Reading too much into this makes it easy to assume that lens features have magically changed; they haven't. As Richard says, we've done this discussion a few times, and I refer people to other threads with far too many of my posts in them.

    As for trolling, I don't seen an issue with Hocus's question; I've switched systems in the past myself, and still maintain some of my Eos kit. Personally, I've not used this particular combination, nor switched between sensor sizes in my Nikon system (although I imagine that the viewfinder cropping of the D3 makes this easier than the D700). It feels fiddly, but I can't definitively justify that - as the OP says, you're effectively using each camera as a body cap for the other one.
     
  26. >>> ..the exotic 24/1.4 becomes a boring 35/2.2 on crop camera.

    Can you provide some example photographs, or explain in detail?'

    Jeff hit it on the head with: "Lenses aren't boring. Photographs can be boring, photographers can be
    boring, but a lens is just a tool."

    >>> That was such a bland, boring remark... sigh.

    What about that statement do you find lacking? It really is the crux of the matter...
     
  27. Brad: If you create an image with the entirety of the sensor on a DX camera (with a sensor 1.5x smaller in each direction than an FX camera) used with a 24mm lens at f/1.4, the field of view and depth of field will match that of a 36mm (24 x 1.5) lens used at f/2.1 (1.4 x 1.5) on a full frame camera placed in the same place and with the exposure adjusted accordingly (either by multiplying the ISO or the exposure time by 1.5 x 1.5 = 2.25). This comes from the geometry of the scene. It's not easy to set multiples of 1.5 in the aperture or ISO; it's easier to compare a fictional 2x crop. Sadly my camera's having a sensor clean, otherwise I'd generate some images to prove my claim; I'll have to do this at some point anyway, so I'll try to come back to this thread.

    As for "why is a 35mm f/2.2 boring", I suspect the OP just meant "non-exotic" (because f/2.2 isn't especially fast for a 35mm prime) and "incapable of the creative choice of an extremely narrow depth of field" - not that this is the only aspect in making a non-boring image. But I can see that, if you're shopping for expensive primes, a 35mm f/2.2 might not seem exceptional.

    I'd taken the "bland, boring remark" as being tongue-in-cheek because the sentence it referred to used "boring" repetitively. I may have been overly-generous. Still, in the implicit context of "I've just paid for a 24mm f/1.4, I wish it worked as a 35mm f/1.4 instead of as a 35mm f/2.2, perhaps I should buy a new lens instead of another body" I can see that perhaps a lesson in avoiding NAS might not have been welcome, however well-intended.
     
  28. I would like to give a big +1 on Dan Browns last comment and I would also like to give a big +1 on Brad's last comment.
    Unfortunately my degree is not in Physics or Optical theory, its only in Photography.
    I have shot a variety of formats from 1.5 crop DSLR to 8X10 and I have understood for many years that the same focal length lens will behave differently on different formats.
    Do I ever use effective f/stops? Nope it would just confuse my light meter.
    Sometimes I think these kind of discussions get WAY to deep and I really feel that this one may have been started just to see how far it would go...
     
  29. I strongly disapprove of anyone plugging numbers into an on-line depth of field calculator and trying to extrapolate from the result - the magic in the box isn't that complicated. (Not to suggest that Craig does this, I just don't think it's the right way to learn about what's going on...​
    The thing is, I suspect this is exactly how the OP came up with his idea that f/1.4 on FX is "equivalent" to f/2.2 on DX.
    It's much less confusing to think of the geometry of the real world. If we first set up two lenses so that two cameras with different sensor formats have exactly the same field of view (by scaling the focal length of the lens by the difference in sensor size), and we eventually intend to produce prints of the same total size from each, the depth of field is solely determined by the size and position of the entrance aperture: there's a cone of confusion passing from the entrance aperture through every point in the focal plane in the scene. What goes on behind the lens has no effect on this - to get the same depth of field (and size of background blur) it's the entrance aperture size that matters.​
    Sure, except that you scaled the focal length because of the sensor behind the lens in the first place, so you do indeed have a dependency on the sensor. If people want to talk about the effect of different sensors, it makes more sense to me to isolate the sensor as a variable by keeping everything else constant; so I wouldn't scale the focal length, which is a property of the lens. Field of view, on the other hand, is derived from the combination of focal length and sensor format, so if the lens is kept constant, field of view will vary with the sensor size. What this all boils down to is that if the only physical change you make is to replace the sensor with one of a different format, DOF will not change, but field of view will. DOF only changes as a consequence of some other change that you make: either to the focal length, the aperture, the physical distance from the camera to the subject, or the degree of magnification in a print or other means of presentation.
    I would hope that DoFmaster scales the CoC down by the crop factor...​
    I've never checked the numbers to see how exactly they derived their CoCs, but they do use smaller CoC values for smaller formats, presumably on the assumption that all images will be printed at the same size regardless of the type of camera used.
    I'm not convinced the "crop factor" is ever a useful concept for novices who don't come with a predisposed idea of the field of view of an 85mm lens...​
    Yes, I agree. Where it really causes a lot of mischief is that focal length and aperture are not just about field of view and DOF, and casual statements about what a lens is "effectively" like on a different format often are not stated precisely enough to make it clear what equivalences are and are not intended. This leads to a lot of confusion. I never express these ideas in that way. Instead, I like to say that a 50mm lens on DX gives a field of view similar to a 75mm lens on FX due to the cropping effect of the smaller sensor. This states the relationship clearly and explains the reason for the difference; and it doesn't even imply that FX is necessarily the ideal standard of reference.
     
  30. Craig --
    I understand the mathematical concepts behind DOF, but as you mention there are several variables that need to be taken into account including one's perception of what is in focus.
    As you mention, print size makes a difference...but I may consider something reasonably in focus where you consider it moderately out of focus. (Same thing? who knows...) One's perception of what's in focus is far more important than a mathematical calculation that turns a grey area into black and white.
    DoF and hyperfocal distance will always be highly debated topics... any your math may be better than my math...or more precise...but none of it really matters if you can't see the difference.
    RS
     
  31. Michael - I don't want to drag this out either, but, in your time of using different formats, have you never gone beyond that changing the format changes the field of view and that if you change the focal length to match the field of view for two formats, the depth of field at a stated f-stop is different, and wondered how the depth of field varies? That's all we've talked about here; maybe you've never needed to know, and certainly you don't need to know when looking at your light meter. There seems to be a resistance to the concept of even thinking about this, and - other than not wanting to confuse people who haven't fully grasped the idea (possibly because I explain it poorly) - I've never understood why.

    If someone is genuinely trying to decide between a D300 with a 35mm f/1.8DX and a D700 with a 60mm f/2.8 (say), or is really excited at the DoF possibilities of the latest micro 4/3 f/0.95 25mm lens, I don't see the harm in discussing it (briefly), with big warnings to avoid confusing novices. If we can't, why is it okay to talk about "equivalent focal length" at all?

    Just trying to understand why the concept seems objectionable, not be contrary. I should really set up a web page and just refer to it next time the discussion comes up.
     
  32. Andrew
    First off one of my pet peeve's is "equivalent focal length" As I am sure you know Focal length does not change when going from 1.5 DSLR to 35mm to 6X7 to 4X5 or to 8X10 (BTW I would think 50mm on 8X10 would be unimaginably wide) 50mm is 50mm
    Do I need to know that the DOF can be different as I change formats using that same magical 50mm. Sure I do but do I need to know why? No not really.
    I have no problem with you guys wanting to talk about the whys and hows but I still think the OP started it just to see what he could stir up.
    And I will say that this thread looks like it is going to stay civil which is a nice change
     
  33. I like the expression "equivalent focal length" because it reinforces my faith in the temporal nature of the APS-C sensor size ;-)
     
  34. There you go Dan trying to bring religion into this...:)
     
  35. "The most important effect of the aperture is that it balances against shutter speed to get you the right exposure." - No, no, no, no, noooo! The most important effect of aperture is to control depth-of-field. Simply balancing aperture against shutter speed removes any aesthetic judgement from your hands and gives it to the camera's dumb exposure meter.
    WRT the difference in depth-of-field versus format size: I think someone's got their circles of confusion confused.
    For the same lens and magnification, DoF is directly related to the format size since the C-o-C should be scaled in direct proportion to the format. So if we say that the DX format is 0.7 times smaller than full-frame, then the C-o-C needs to be 0.7 times smaller too. The actual aperture diameter and all the resulting solid angles that go to calculate DoF need to be scaled by the reciprocal of 0.7, which means that there's almost exactly one stop difference in effective DoF between full-frame and DX. Your comparative aperture should therefore be f/2 and not f/2.2.
    See attached depth-of-field Excel spreadsheet.
    This is all theoretical anyway, and it only needs a small focusing error or slight shift in subject distance to make a big difference to the actual depth-of-field.
     
  36. I also find it interesting that Hocus Focus is using a 5DMkII, D700, and D300... The only reason I can fathom is that the OP was second shooting for a pro that lent out a 5DMkII and lenses. Any light shed on this would be helpful.​
    I have my own gear plus I have access to gear from other shooters. We borrow or rent. Big deal.
    I would worry more about the topic rather than debate what's in my bag and what's not. Just saying so you don't confuse yourself.
     
  37. Brad: If you create an image with the entirety of the sensor on a DX camera (with a sensor 1.5x smaller in each direction than an FX camera) used with a 24mm lens at f/1.4, the field of view and depth of field will match that of a 36mm (24 x 1.5) lens used at f/2.1 (1.4 x 1.5) on a full frame camera placed in the same place and with the exposure adjusted accordingly (either by multiplying the ISO or the exposure time by 1.5 x 1.5 = 2.25). This comes from the geometry of the scene. It's not easy to set multiples of 1.5 in the aperture or ISO; it's easier to compare a fictional 2x crop. Sadly my camera's having a sensor clean, otherwise I'd generate some images to prove my claim; I'll have to do this at some point anyway, so I'll try to come back to this thread.​
    Exactly. I'm shocked so many (though not all) of you pass for gear experts but don't know the basic implications of different sensor sizes. There's more than FoV changing; DoF is also altered.
    "The most important effect of the aperture is that it balances against shutter speed to get you the right exposure."
    - No, no, no, no, noooo! The most important effect of aperture is to control depth-of-field. Simply balancing aperture against shutter speed removes any aesthetic judgement from your hands and gives it to the camera's dumb exposure meter.​
    Exactly. Someone got it right!
    As for "why is a 35mm f/2.2 boring", I suspect the OP just meant "non-exotic" (because f/2.2 isn't especially fast for a 35mm prime) and "incapable of the creative choice of an extremely narrow depth of field" - not that this is the only aspect in making a non-boring image. But I can see that, if you're shopping for expensive primes, a 35mm f/2.2 might not seem exceptional.

    I'd taken the "bland, boring remark" as being tongue-in-cheek because the sentence it referred to used "boring" repetitively. I may have been overly-generous. Still, in the implicit context of "I've just paid for a 24mm f/1.4, I wish it worked as a 35mm f/1.4 instead of as a 35mm f/2.2, perhaps I should buy a new lens instead of another body" I can see that perhaps a lesson in avoiding NAS might not have been welcome, however well-intended.​
    Andrew got it all right. Hope this clarifies everything.
    Now let's get back to the discussion... What I'm worried about most is that with the kit mentioned, either you're at 24 and 135mm, or at 35 and 85mm. I find myself most often at 24mm 70mm and 135mm so I might throw in a cheap 50/1.4 which on crop camera produces the FoV of a 75-80mm lens (and maintin the 24mm on full frame).
     
  38. >>> Brad: If you create an image with the entirety of the sensor on a DX camera (with a sensor 1.5x
    smaller in each direction than an FX camera) used with a 24mm lens at f/1.4, the field of view ....

    Huh? I have no idea at all why all that was addressed to me. Oh well... I was commenting on lenses being characterized as "boring." Odd as that's something I've never heard from a *photographer*. Which is different from a gear enthusiast/expert/owner, etc.

    >>> Exactly. I'm shocked so many (though not all) of you pass for gear experts but don't know the basic
    implications of different sensor sizes.

    You're assuming a lot, calm down. Is that the test, passing as a "gear expert?" In any event, I'll let my photos speak...
     
  39. You'd get better quality by getting a full set of lenses for use on the D700. Theoretically mixing formats sounds nice but DX just doesn't work well with really fast lenses (at wide apertures).
    A 35/1.4 AF-S on the D700 in particular is much better than the 24/1.4 on a DX camera (mine is the D7000). What's more you lose the robustness (due to ease of focus) and high ISO advantages of the D700 over the DX camera.
    But that's just my experience and viewpoint; you can do what you want with your gear. There is one advantage to using the 24/1.4 on DX; you get less distortion, but then everyone says it's easy to correct in post (in this case, it is, but you do lose precise framing).
     
  40. I'm shocked so many (though not all) of you pass for gear experts but don't know the basic implications of different sensor sizes. There's more than FoV changing; DoF is also altered.​
    What creates the impression that a smaller sensor has more DOF is either the shorter focal lengths typically used with smaller sensors, or greater camera-to-subject distance used to compensate for narrower angle of view. Against this, there is the greater magnification needed to produce a print of a given size from a smaller sensor, which actually reduces DOF (obviously, since it is the reason that smaller CoC values are typically used with smaller formats, and a smaller CoC value will result in less DOF if other parameters are kept constant). But the sensor isn't really doing any of this.
    One could argue that smaller sensors lead photographers to choose shorter focal lengths or to stand farther away from their subjects, and that these choices result in greater DOF than would be obtained making comparable choices with a larger-format sensor. But the difference in DOF is actually caused by the shorter focal lengths or greater physical distances, not by the sensor.
    It's kind of funny that although you argue above that "a smaller sensor produces more depth of field", your own "equivalences" actually show the opposite. According to your original post (and also dofmaster), a 24mm f/1.4 lens has to be stopped down to f/2.2 to give about the same DOF on DX that it would have at f/1.4 on FX. In other words, using dofmaster's CoC values for DX and FX, the same focal length actually gives less DOF on DX than on FX, not more. This effect comes from the smaller CoC value, as I said above. It's only when you change the focal length or focus distance to compensate for the narrower field of view that you end up with more DOF. This makes quite clear what I've been saying all along, that greater DOF comes from a change in the lens, not the sensor.
     
  41. Huh? I have no idea at all why all that was addressed to me. Oh well... I was commenting on lenses being characterized as "boring." Odd as that's something I've never heard from a *photographer*. Which is different from a gear enthusiast/expert/owner, etc.​
    Ah, sorry Brad - I wasn't sure whether you were querying the equivalence (from some perspectives) of the 35mm f/2.2 with a 24 f/1.4, or whether you wanted examples of a 35mm f/2.2 being "boring". The latter is a bit harder to answer - I could argue that it provides slightly fess creative flexibility than a 35mm f/1.4, but I'd put "boring" down to an awkward turn of phrase. My bad.
    This is all theoretical anyway, and it only needs a small focusing error or slight shift in subject distance to make a big difference to the actual depth-of-field.​
    Absolutely, RJ. And apertures and focal lengths aren't precise anyway. Still, it's a starting point; knowing what should be going on in an ideal world has some appeal. I finally have some demonstration images (having remembered that I own another DSLR), but I'll save them for the next time this comes up, and it is hard to transfer theory to the real world, even if the theory is valid. I come to photography from the world of computer graphics; these things are much easier in virtual reality...

    Michael - thank you; it helps to know where you're coming from. Hocus - glad to help; while people are a bit fraught, though, let's avoid to many assertions about what people don't know? I may have a handle on the geometry here, but I won't claim any talent at composing an image, and while I found understanding the depth of field behaviour an interesting intellectual distraction, I can see that it's in the category of things that many people never need to know. (If it helps, I have almost no idea how to use an incident light meter or make a contact print.) First rule of the internet: if someone has said something offensive, always assume that they didn't mean to. (I prefer to think of everyone on the planet as mild-mannered and incompetent rather than actually out to get me; much better for my self-esteem). Second rule of the internet: try not to say anything that could be construed as offensive. Don't get me started on rule 34.

    Back on topic, one point in favour of the single body approach: I suspect most people would upgrade their bodies more frequently than their lenses. Deliberately maintain a system with two bodies, and you'll be keeping them both up to date. But maybe this would happen anyway.

    I appreciate the lack of flexibility in being stuck with 24 + 135 or 35 + 85. I've been thinking of picking up a DCS Pro14n so that I have a cheap(ish) second body which can use my lenses as on my D700 (except more slowly and without the low-light handling). I have an F5 for similar reasons - I'd rather do that than get a crop sensor. Still, if you're doing pro shoots, I doubt that's practical. For the amount of money you seem to be prepared to drop, I'd be seriously tempted to hold on in case Nikon announces a D3x replacement this year. If the D3x (or a D700 equivalent with the D3x sensor) becomes cheap, DX crop mode in-camera is far more practical than on a D700/D3 and you wouldn't even have to switch lenses. (I'm assuming you want the really shallow DoF option rather than low light; otherwise the traditional wedding recommendation of a 70-200 is made awfully practical by its VR.)

    But that's my $.02. All I know about wedding shoots is that I should avoid getting volunteered for any. Good luck with whatever solution you try.
     
  42. Craig - we're only talking about using a lens on a DX body to provide the equivalent field of view as a lens which he might have considered buying separately were he to use an FX body alone. That is, we're considering a lens used on DX as a "virtual" lens which might be owned for the FX body, first in terms of field of view (and therefore focal length), and secondly in terms of the depth of field compared with the FX lens. "Equivalence" means "what lens (and aperture, and exposure/sensitivity difference, if we care about these things) will produce the same image if used on an FX sensor as the lens (and aperture, and exposure, and sensitivity) that I'm using on this DX sensor?" Not "what happens if I try to create a different image", either by discarding some of the sensor area, using the same lens on different sensor formats, or moving the camera. All these are valid questions, but not what we're considering.

    You're right that there's nothing magic about the DX sensor. You can enlarge part of any larger format and have to do similar calculations; a teleconverter also has a very similar effect, as does simply changing the focal length of the lens. Nonetheless, the calculations work.

    Your last paragraph is correct: a 24mm f/1.4 used on an FX body does have more depth of field (for the same image size) than the same lens used on a DX body if the full-sensor images are scaled to the same print size, due to the differing image magnification. However, it also presents a completely different field of view on the two bodies. We're not comparing the two dissimilar images, both taken with a 24mm lens - we're talking about two similar images (or at least, the ability to create images), one with the 24mm f/1.4 on a DX body and one with a 35mm lens on an FX body. Comparing the 24mm used on two bodies is similar to comparing the 24mm with a 35mm, both used on an FX body - an equally valid thing to talk about, but not the current subject of discussion.

    I hope that helps clarify things. (There are lots of things we could be talking about here, and there's only going to be frustration if we're not all talking about the same thing.)
     
  43. What Craig said several pages back. Do the experiment.
     
  44. Oops, I missed one of Craig's posts (Ron - is this what you meant?)
    Sure, except that you scaled the focal length because of the sensor behind the lens in the first place, so you do indeed have a dependency on the sensor. If people want to talk about the effect of different sensors, it makes more sense to me to isolate the sensor as a variable by keeping everything else constant; so I wouldn't scale the focal length, which is a property of the lens. Field of view, on the other hand, is derived from the combination of focal length and sensor format, so if the lens is kept constant, field of view will vary with the sensor size. What this all boils down to is that if the only physical change you make is to replace the sensor with one of a different format, DOF will not change, but field of view will. DOF only changes as a consequence of some other change that you make: either to the focal length, the aperture, the physical distance from the camera to the subject, or the degree of magnification in a print or other means of presentation.​
    I apologise for not clarifying. I'm working with the premise that we're talking about the context where "equivalent focal length" is a short-hand for "lens with focal length a on sensor/film format b produces the same field of view as lens with focal length c on sensor/film format d" (and I, too, try to state this only in terms of the sensor/film sizes we're discussing). I believe this was the case the OP was talking about, and nothing else. To me, it doesn't make sense to describe two images that have a different field of view as "equivalent" in any way, although you can certainly compare depth of field and potentially note that the two - visually very different - images were taken with the same lens focal length and possibly aperture.

    The point I was trying to make is that adjusting the focal length to compensate for sensor size and match the field of view is something that can happen "behind the lens". It has no effect on the view of the entrance aperture that the scene has - that depends only on the size of the entrance aperture in absolute terms, and on the lens position. If you don't keep the field of view constant, the situation alters. However, I really think that it was clear what was being discussed as of the original post, which explicitly mentions effective apertures in the context of effective focal lengths. Ignore the "effective focal length" bit and the "effective aperture" is another story.

    And I've done a terrible job of not getting dragged into this discussion again. Sorry.
     
  45. I'm working with the premise that we're talking about the context where "equivalent focal length" is a short-hand for "lens with focal length a on sensor/film format b produces the same field of view as lens with focal length c on sensor/film format d" (and I, too, try to state this only in terms of the sensor/film sizes we're discussing). I believe this was the case the OP was talking about, and nothing else.​
    Actually, I don't think that's what the OP said. He was talking about using FX and DX bodies to be able to use two lenses as if they were four: the 24mm and 85mm lenses doing their usual wide and near-telephoto work on FX, while becoming "effectively" near-wide 35mm and mid-telephoto 135mm on DX. Nothing in the original post suggests trying to match the field of view between FX and DX bodies; indeed, it seems pretty clear that what he wanted was to have four options (or at least a choice between two pairs of "effective" lenses) for framing.
    He did mention matching FOV and DOF between formats in some later comments, but only, I think, in the context of explaining why he thought sensor sizes affected DOF, which is sort of tangential to the original post (as indeed is most of the discussion that followed).
     
  46. Hi Craig. Glad you haven't given up on me in disgust. :) The OP wrote:
    In terms of field of view and depth of field, this gives effectively 24/1.4, 35/2.2, 85/1.4 and 135/2.2.​
    I'm pretty clear that this means "were I to use the 24mm and 85mm f/1.4 on both bodies, the lenses on DX would behave as if I had 35mm and 135mm f/2.2 and only used an FX body" (ignoring exposure). As far as I know, the whole DoF vs sensor size tangent was only in this context. I may have missed an ambiguity, in which case I apologise.
     
  47. I think this thread is blown out of proportion...
    FWIW I use both a 24 and 85 but for backpacking (not wedding) but I add the 17-35mm as well. Between the three lenses and a FX/DX combo, I find it great for minimizing the load. The DOF issue is about one stop more on DX. The multiple FOV/less lenses is the advantage...I have done this for a long time now while most forumers frown upon this very idea. Folks, it's isn't rocket science...use it to your advantage.
     
  48. Well said, Leslie. Perhaps this would be a good time to mention the Nikkor to micro-4/3 adaptors for another crop ratio? :) (This isn't entirely facetious; at some point my partner will actually get one - the E-PL3 actually looks interesting - and in good light for static targets, I'm looking forward to mixing things up.) I suspect a Pentax Ricoh Q system might be going a bit far, though.
     
  49. Yeah, Andrew, the new m4/3s have my attention as well. A 50mm cheap nikkor would make a great portrait lens on the oly especially w/IBIS.
     
  50. I love my 35/2 on Fx. When I make boring pictures, it's certainly not the lens' fault.
     
  51. I think this thread is blown out of proportion...
    FWIW I use both a 24 and 85 but for backpacking (not wedding) but I add the 17-35mm as well. Between the three lenses and a FX/DX combo, I find it great for minimizing the load. The DOF issue is about one stop more on DX. The multiple FOV/less lenses is the advantage...I have done this for a long time now while most forumers frown upon this very idea. Folks, it's isn't rocket science...use it to your advantage.​
    Thanks Leslie. Finally a sensible post. What bodies do you use?
    Equivalence aside, how many of you actually own or use 24/1.4 and 85/1.4 ?
    I find myself quite often at both ends of 24-70/2.8 and at 135/2.
     
  52. Thanks Leslie. Finally a sensible post.​
    You know how to make friend and influence people, don't you? :)
    Equivalence aside, how many of you actually own or use 24/1.4 and 85/1.4 ?

    I find myself quite often at both ends of 24-70/2.8 and at 135/2.​
    I recently acquired a Samyang 85mm f/1.4, and I like the field of view and DoF so far on FX (likewise the Tamron 90mm that was my short portrait lens until recently). I like 135mm, and own the DC, but don't get along with it especially well; that's not the focal length, though, and I'm happy with a 135 f/2.8 AI when I have time to focus it, but you have to walk a long way away if someone asks for a group photo with one. I have a 14-24, which I use throughout its range for landscapes and architecture, but rarely for shots of people except in very confined conditions - the distortion when the image is viewed at a normal distance is too pronounced for me. I use the 28mm end of a cheap zoom more with groups, and I have an eye out for the 35mm f/1.4 Samyang for candid groups in low light. For what it's worth, I'm usually either wide or medium/long tele - I rarely use 50mm (I use 200mm more than the 50mm, both to stay off the radar of the subject and to control the background). I can't imagine wanting the 24mm f/1.4, given how much it costs and given that I already have the 14-24, but YMMV. It's a lens that I'm happy exists, like a Noctilux, the 300mm f/2 or the 6mm f/2.8.

    I suspect I'd use the wider lenses with people more if I were to pose groups rather than just take candids, which by their nature tend to involve fewer people and longer distances. I hope that sample, albeit from an amateur with NAS, helps.
     
  53. Thanks Leslie. Finally a sensible post.​
    You were accused of trolling earlier in this thread. I still think your original question was meant seriously, but now that you're resorting to flamebait, I begin to understand why some people thought otherwise.
    There was an observation above about how nice it was to see a disagreement that remained civil. This is because Andrew and I are both civil people. There may be a lesson in that for you.
    Equivalence aside, how many of you actually own or use 24/1.4 and 85/1.4 ?​
    I own a number of 24mm and 85mm lenses (also 35mm and 135mm, the "effective" focal lengths you originally mentioned) for different cameras. None of them are actually f/1.4, mostly because I find that better performance is usually obtained from f/2 or f/2.8 lenses, which are generally smaller and less expensive too. And it isn't often that I would really want to shoot at f/1.4 anyway.
     
  54. None of them are actually f/1.4, mostly because I find that better performance is usually obtained from f/2 or f/2.8 lenses, which are generally smaller and less expensive too. And it isn't often that I would really want to shoot at f/1.4 anyway.​
    I'd like to pick up on that. In my shooting, it's relatively rare that I actually want a shallow depth of field as such. I do often want to throw the background a long way out of focus - but if I want to exclude/separate the background, I usually do it with a longer lens. I concur with Craig that all the f/1.4 lenses I've seen are far from perfect at that aperture; I'd far rather use a 135mm or 200mm at f/2 than an 85mm at f/1.4. I ended up with a Samyang 85mm f/1.4 because it was cheap enough that I could live with its compromises when I need a bit more perspective or less working distance than the longer lenses offer me - I'd not pay the going rate for the Nikkors. I raised tentative concerns above about the quality of the DX subset of an 85 f/1.4 used wide open compared with a 135mm f/2 on FX; I'm sure this behaviour factors in to the high quality associated with medium format lenses, and I have to say I'm tempted to use a 150mm f/2.8 on a 5x4 if I want a shallow depth of field portrait (one of several reasons I'm looking at view cameras).

    Wide f/1.4 lenses have their use, but given that they won't lose a background nearly as well as a much less exotic longer lens, I tend to consider a fast wide lens as a low-light option (partly because hand tremor is less an issue) rather than being needed for creative depth of field. Besides, with a wider angle lens, I usually want a large amount of subject in focus. Hence my doubting that I'd ever use a 24 f/1.4; I'll be interested in how useful others find it. I'm more tempted to get a 20mm f/4 as a more portable option than the 14-24.

    Of course, I'm simplifying - a 24mm f/1.4 will separate the background more than an f/2.8 version, and this can be useful creatively - but in general that's not how I think of ultrawide lenses. Maybe that's a failure of my creativity.
     
  55. Per Craig p3:
    "Here is a thought experiment: In a controlled studio environment, with a stationary tripod, shoot a scene using the same 24mm f/1.4 lens at f/1.4 using both FX and DX cameras. Print the resulting images at, say, 20x the size of the sensor. Then crop the FX print to match the narrower framing of the DX print. How do the two resulting prints differ?" (Answer - not much, at least in DOF)
    ...and not to be argumentative: the depth of field is dependent on focal length, aperture diameter (not recalculated f-number), and distance to the subject only. Cropping part of the picture out (either after the fact with scissors, or at the time of exposure with a smaller sensor) doesn't change any of these 3 things. A finer resolution sensor or slow film could make a difference in the circle of confusion, but this would be small. The DOF preview button stops the aperture down so one can eyeball/estimate it before shooting.
    Regarding the original post:
    "First, while 135/2.2 is still impressive for portraits and sports, the exotic 24/1.4 becomes a boring 35/2.2 on crop camera." (Answer - it becomes a 24/1.4 which has had the top, bottom, and sides cut off.
     
  56. I'll revisit this quickly, because I've got the images...

    Ron - apologies for not understanding your previous post (I also have paging turned off, which means "p3" confused me!) When discussing depth of field in the context of its relationship to aperture, I always assume that the definition of circle of confusion that we're using is defined in terms of the smallest detail that you can see which will appear as sharp as your eye can distinguish (possibly under poor viewing conditions). If the sensor resolution or film grain defines depth of field, the aperture is not the limiting condition - and possibly none of the image is truly sharp.

    If the ability of the eye to detect that an image detail is out of focus is the limiting factor, image enlargement (or at least, field of view of the final print from the viewing distance) is a factor.

    To restate the three cases we might consider: 1) Cut the edges off a print and its DoF doesn't change; use the same lens on cameras with different sensor sizes and produce a print whose size is proportional to the sensor size, and the DoF is unchanged. 2) Increase the print size of the smaller sensor to match that of the larger sensor, and the smaller sensor has a reduced depth of field (because it's enlarged more, so a just-visible circle of confusion in the print corresponds to a smaller circle of confusion at the sensor). The field of view of the two prints obviously differs. 3) Fit a lens with a longer focal length on the larger sensor camera to match the field of view of the smaller sensor, and to get the same depth of field, you need the same entrance aperture, which means the f-stop has to reduce by the crop factor - not keep the same f-stop (as you might suspect if you've just been told that the FX equivalent of a 24mm lens used on a DX camera is a 35mm lens, and no other information). In the context of choosing different sensor sizes (or lens focal lengths) to get different fields of view, and considering the relationship between the field of view and depth of field with a given lens on two formats, we're looking at case 3 only.

    Example images, because I've got them, follow. I hope this helps clear up any further confusion.
    00Yyx4-375555584.jpg
     
  57. Now with a 105mm lens (ish) at f/5, from the same location. The reduced scaling means that the background is less blurred, and the depth of field is increased compared with the 210mm f/10 image.
    00Yyx8-375557584.jpg
     
  58. Now the middle cropped from this image (as per a 2:1 crop factor sensor) and enlarged to the size of the original. Blur of the background closely matches the 210mm f/10 image (within experimental error and my ability to actually hit exact focal lengths). Therefore we could say that an image taken at 210mm f/10 matches the image with a 2x smaller sensor at 105mm and f/5 (if exposure is balanced - which in this case I did by quadrupling the exposure time with the lens at 210mm), and therefore these lens/focal length pairs on the two sensors are "equivalent" (if we balance exposure). I believe this is the only type of "equivalence" that we're discussing; I hope that clears up any confusion.
    Actually, all these images were taking with a 1.6x crop-sensor Canon. Just to prove that there's nothing magical about DX and FX, and for irony (and not at all because my D700 is off being cleaned).
    00YyxA-375559584.jpg
     
  59. d700 and d200
    I use a 24mm but not the 2k F1.4. I rarely put the 85mm on DX and the 24 on FX. Usually, I have the zoom on one cam while either the 85 or 24 on the other. Depends on the available light as well, of course. I'm street shooter mostly.
     
  60. "DOF is not, in fact, any different at all" - Ah but it is! D-o-F is affected, among other things, by the amount of magnification that the image has to undergo to produce the final viewing size, either in print or on screen. Six pages of "discussion" and that point still clearly hasn't got across!
    Let's try and set out exactly how D-o-F is affected:
    Case (1) - same lens, aperture and subject distance; different format size. D-o-F decreases as the format size gets smaller in direct proportion to the circle of confusion chosen. This is simply due to the extra image magnification needed for final viewing and is linear.
    Case (2) - same field of view, same aperture and subject distance (in other words we get exactly the same picture, but on different formats with an appropriate change in lens focal length). D-o-F increases as the format size decreases. The F-number needs to be altered in direct proportion to the linear change in format size to maintain the same D-o-F.
    Case (3) - same format, same aperture, same subject distance, different focal length lens. D-o-F decreases with increase in focal length. D-o-F is in inverse geometric proportion to increase in focal length. The relative aperture must increase as the square of the increase in focal length to maintain the same D-o-F. For example if you double the focal length then the aperture number needs to increase fourfold.
    When we combine these cases, it's easy to see that a change in focal length effectively trumps all other changes, and everything else follows. Which is why a smaller format generally gives greater D-o-F for the same aperture, but only if the field of view and subject distance remain the same. If the focal length and aperture stay the same then D-o-F reduces. Clear?
    Just to reinforce the point, here's my depth of field calculator again with a few values inserted. I've also added a total depth column to make it easier to see any differences and similarities.
    And yes, depth-of-field is confusing for newbies, but it seems it's also confusing for everyone else!
     
  61. "DOF is not, in fact, any different at all" - Ah but it is! D-o-F is affected, among other things, by the amount of magnification that the image has to undergo to produce the final viewing size, either in print or on screen. Six pages of "discussion" and that point still clearly hasn't got across!​
    Wrong. I've referred to greater magnification of prints or other display media as a factor in DOF several times. I've also noted that a smaller CoC value reduces DOF, and the reason you use a smaller CoC value with a smaller sensor is because of the assumption that all images will be displayed at the same size regardless of the sensor used (i.e. that images from smaller sensors will be magnified more when displayed). This is a conventional assumption, not a fact of life, and all it does is obscure the real relationships involved, leading people to think, incorrectly, that the sensor size, by itself, has a direct effect on DOF, which it does not and could not.
    DOF changes as a result of a change in focal length, subject distance, or display magnification. The sensor itself is at best indirectly associated with this. You may choose a shorter focal length because you are shooting with a smaller sensor, but that's a choice you make based on your own artistic intent. The sensor is not doing it, you are.
    Your examples are cluttered with irrelevant and unnecessary assumptions that only serve to confuse the issues. You want display size to be the same for all images, and you also want field of view and subject distance to be kept constant. These assumptions obscure what's really happening. If the sensor size changes, a narrowing of the field of view is the only direct consequence. If focal length, subject distance, or display magnification change, it's because you decide to compensate for the change in sensor size. Those compensations are actually what changes DOF. The sensor is not doing it, you are.
     
  62. Craig: You could take a photograph with a 100mm f/2.8 lens. Mount it on a 5x4 camera or an APS camera and make a contact print, and I agree that the depth of field is identical - the larger format merely provides a much larger field of view and a much larger final image. In my opinion, it would be odd to consider two such prints as in any way equivalent - they present an entirely different scene to the viewer.

    We talk about "equivalent focal length" because most people choose their lens focal lengths in order to control the field of view on a sensor (or film format that they own). If you're used to thinking "I need a field of view that matches a 50mm lens on a 35mm camera" and I have a DX format camera, it's useful to know that a 35mm lens is (roughly) what you need. If you put a 24mm lens on a DX camera, it's nice to be able to think about what lens would have given a similar field of view on a 35mm full frame, if that's what you're used to. Maybe naming lenses in terms of their angle of view on a standard format would have been preferable, but we have precedent for the current scheme. Doing otherwise means that you need to work out the (not clearly stated) sensor size of your compact camera in order to work out the field of view of its 8mm lens. And if you're going to think in terms of "equivalent focal length", it's just as valid to think about the depth of field of the "equivalent" lens that you're imagining.

    Similarly, most people, in my experience, do not use their sensor size as a factor in deciding how large a final image will be printed (for example, I've never met a camera that actually puts the sensor resolution into the EXIF ppi field). That the actual scale factor is different may be an indirect consequence of this, but I've never met someone who thinks "I need to enlarge the negative by 10" rather than "I'd like a 10x14 print".

    So, true, it's not the sensor size that causes any depth of field changes: it's the differing ways in which most people would want to treat the image produced on these sensors. Does this "confuse the issues"? Well, if you don't perform different image scaling, there are no issues to consider; the entire point of talking about "equivalent" focal length and depth of field is when you want to produce the same image from two formats different formats. It's hard to call this an "irrelevant" or "unnecessary" thing to want to do, at least in the context of this discussion, which is explicitly about using two formats to take advantage of this precise difference. If you switch from FX to DX and you know what effect you want, it's simple enough to increase the focal length by a factor of 1.5 and decrease the f-stop by a factor of 1.5 (and either let the camera worry about the exposure, or increase ISO by 2.25x). Even though I could, I don't work out everything from scratch given the sensor measurements and a calculator with transcendental functions. (To bring this vaguely back to the OP's question: I don't find scaling small numbers by 1.5 to be confusing.)

    I was just putting a web page together so I don't have to discuss this again. Then I thought "this is dull, I'm wasting a Sunday, and the tennis is too interesting; I'll just check Photo.net..."
     
  63. Andrew, you might benefit from reading Section 3 on exposure in that book "The Negative" LOL.
    Just kidding ;-)
     
  64. :) I'm glad someone appreciated my attempt to produce a pretentious sample image - it was this or a sleeping cat. I'll admit that I didn't use the zone system, though. I actually had to increase the exposure by two stops in RAW conversion - I was so concerned with framing that I forgot to bring up the histogram, and the meter was thrown by the black and white areas - but I did the same for all the images. I've read The Print too, and don't think Ansel would mind too much. The effect of lens and format changes on field of view and depth of field is, of course, in The Camera, although (IMHO) some diagrams would have helped, and "depth of field changes with the square of the focal length" could have benefitted from "linearly due to magnification and linearly due to the increase in aperture". But the results are more useful than the working. Oddly enough, I doubt Ansel ever carried a 10x8 and a 5x4 to increase his lens range...
     
  65. Well, sidestepping the whole DoF issue, I think shooting a D300/D700 combo with a fast 24 and a fast 85 would make sense. In fact it's what I hope to end up with eventually. I think at ISO 1600 both camera's would yield good IQ and the similar button lay out would work easy. I'd add a 50/1.4 and then have the following (for me most useful) options:
    -wide + short tele (D700/24+D300/50)
    -standard +short tele (D300/24+D700/85)
    -standard + medium tele (D700/50+D300/85)
    -wide + medium tele (D700/24+D300/85)
    At arrival at an event I'd assess the situation and chose the most appropriate combo, leaving just one 'redundant' lens in the bag. That way I'd foresee not much lenschanging or confusion...
     
  66. Craig, any attempt to calculate or quantify depth of field must take into account the magnification needed to view the image. Any depth of field calculation needs to be based on a suitable circle-of-confusion and this needs to be chosen to reflect both the format size and an "average" print size and viewing distance.
    The standard way of choosing a suitable c-o-c is to divide the format diagonal by some constant - usually a number somewhere between 1500 and 1750. (Now personally I have strong objections to using the image diagonal for any comparative purpose, but that's another issue.) Anyway, whether we use the format diagonal or some other metric, the c-o-c always needs to be linked to the original image size - i.e. the camera format.
    If we throw away this linking of c-o-c to format size, then there can be no depth of field calculation. So either you accept that the format size is integral to the calculation of depth of field, or we don't have any depth of field calculation to argue about, and we can all give up and go home. The fact remains though, that such a thing as depth of field exists. So are you saying that we shouldn't even attempt to quantify it?
     

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