Check my math...?

Discussion in 'Medium Format' started by martinangus, Sep 30, 2011.

  1. If I put a Hasselblad 6x6 medium format lens onto my Nikon DX body...would the lens behave as follows:
    100mm Medium Format lens used on a 135 film format body = 167mm
    and
    167mm 135 film format lens used on a DX format body = 278mm
    Math:
    Medium format to DX format = 2.78x
     
  2. No. There is no math to apply.<br>A 100 mm lens is a 100 mm lens, and 'behaves' like a 100 mm lens on all formats.
     
  3. lol. You guys crack me up.
     
  4. The word "behaves" is in reference to field of view or crop factor. I would assume that the benefit of using a MF Zeiss lens on a Nikon DX is two-fold. 1. Better optics and 2. the crop forces the sweet spot.
    No?
     
  5. As Q.G. de Bakker said, "A 100 mm lens is a 100 mm lens, and 'behaves' like a 100 mm lens on all formats."
    Don't matter if it a postwar Nikkor, DX, FX, Bronica or an enlarger mount, or any other brand name.
    Edit: It would truly be magic if what you stated did happen. :)
     
  6. To produce a print of equal quality from a DX format camera, compared to a medium format camera, you need a much higher quality lens on the DX camera as the captured image area is a small fraction of the medium format camera. A Hassy has a film image area of approx56x56mm or 3,136 sq mm. A Nikon DX format sensor is 23.7 x 15.5 mm or 355-372 sq mm, depending on which camera you pick.
    So for the same field of view, the lens has to pack the same amount of visual information into approx one tenth the area. It had better be a real good lens.
    Here is a half decent article on the different sensor sizes. http://en.wikipedia.org/wiki/Nikon_DX_format
     
  7. Martin, you were doing fine with your math until you threw the lens length into it<g>. However, if you are looking for the equivalent FOV of the 100mm lens on 6x6, but for DX, you could start with this fantastic website ;-) http://www.hasselbladhistorical.eu/HW/HWequifoc.aspx, and use 1.7 for conversion between 35mm and DX. But that's not what you were asking.
     
  8. It might not be worth doing this. See http://www.graham-mitchell.com/blog/?p=152
     
  9. Mainly, it's not worth doing this because the hoped for miracle (almost tripling the focal length of a lens) will not happen.<br>A 100 mm lens is a 100 mm lens, and the field of view of a 100 mm lens on a format (any format) is that of a 100 mm lens (any 100 mm lens) on that format.<br><br>So:<br>100mm Medium Format lens used on a 135 film format body = 100mm<br>and<br>100mm 135 film format lens used on a DX format body = 100mm<br><br>Math:<br>Medium format to DX format = 1x
     
  10. You may get an IQ boost. When the 35mm body looks through the MF lens, it only uses the center of the lens. This is usually the best area of optical quality.
    When I was using Olympus digital, I used all my OM lens. Even my mediocre ones were all sharp and contrasty.
     
  11. Leaving aside the bogus focal length comparison. There's no doubt that some of the best lenses you can buy are made for Hasselblad - BUT - those lenses were designed to cover the 6x6cm format with an image circle diameter of ~79mm and a half-angle of 21.6 degrees. They were never designed to cover a piddling image circle of 30mm with a half-angle of 8.5 degrees.
    So why does this matter? Because the painful optical truth is that you can design a lens (of any given focal length) to perform excellently over a small image angle, moderately over a modest image angle or fairly poorly over a very large image angle. So within set limits of cost, weight and physical size, Zeiss (or whoever) will have optimised the design to cover 6x6cm, which basically means that good performance at the edges and corners of the 79mm image circle will have been bought at the expense of some sacrifice of central sharpness. Not only that, but most 'blad lenses are comparatively old designs without the benefit of modern affordable aspherical elements, and newer prime lenses specifically designed to cover the DX format will almost certainly outperform them.
     
  12. That's true, R.J. but ignores one rather important aspect.<br>Make a short focal lens cover a large area, and you run into the problems you describe. But MF and LF lenses are also 'bigger', they 'grow' in proportion with the area they have to cover, meaning the design can be basically the same as that used in smaller formats scaled up, with the problems you describe not occuring.<br>So no "painful" worries there.<br><br>Old vs new is also not that clean cut an issue as one might suspect.<br>They knew very well how to calculate and produce perfect lenses back in the days the slide rule was the most sophisticated aid at the designer's disposal. You can indeed improve lenses by using aspherical elements, but making those is rather expensive, and not done often. Also not, because you can achieve the same results using only spherical lenses.<br>Computer power has made lens design a far less laborious task. But it has mainly been used to design intricate zoom and internal focussing lenses, to find ways too to reduce the amount of glass that autofocus systems have to move. It does that very well, but instead of producing better lenses than the ones that we had before, it is mainly spend on keeping correction on level while zooming/internal focussing/auto focus changes the focal length of a typical modern lens.<br>Sticking with Hasselblad lenses, there are two of them that illustrate the point: the 1950s 38 mm Biogon's 'manual' design is ever so slightly better than the late 1990s 'computer' designed version. And though computer aided design has brought another couple of Superachromat lenses, made it easier to perform this (still expensive) trick, the late 1960s Superachromat quite simply cannot be improved upon. There are examples of this in other maker's lens lines too (MF, 35 mm format and LF): old lenses that are 'still' as good as it gets.<br><br>DX sized sensors are all covered by soft focus filters, reducing the effective resolution to about 40 lp/mm, to tame the beast called aliassing. So there's no point in making 200+ lp/mm lenses for the typical DX-sensor camera (which is also why it makes little sense to put good MF lenses on a typical DX-sensor camera. The sensor, not the lens, is the limiting factor).<br>Besides, we must be careful not to mix up needing to be better with being better yet once again. Yes, to equal the image quality of larger formats, lenses (and films/sensors) made for smaller formats have to be better than lenses made for larger formats. But they hardly ever are. You simply get better images using larger formats (why else would anyone bother with larger formats?)<br><br>The 'bottom line' of it all is that though there indeed are modern lenses that are better than the best we had before (in 35 mm, MF and LF formats), they are not many (and mostly very expensive - i.e. not used much).<br>And that newer lenses designed to cover DX format - if anything - probably are not as good.
     
  13. http://www.photo.net/equipment/medium-format/focal-length-conversion

    http://en.wikipedia.org/wiki/35_mm_equivalent_focal_length

    http://en.wikipedia.org/wiki/Effective_focal_length
     
  14. OK, I think I get it.
    Are the following statements correct?
    1. "The scene is always the same size with the same lens."
    2. "The captured area of the above scene (or image produced) varies depending on the format. More crop for DX less for MF"
    3. "Adapting a 100mm Hassleblad MF lens to a DX body will capture exactly the same sized image as putting a DX lens on that same DX body."
    4. "It is a misconception to state that a DX sensor has more "pull" when using a 135 format lens"
     
  15. Martin Angus , Oct 01, 2011; 01:18 p.m. OK, I think I get it. Are the following statements correct? 1. "The scene is always the same size with the same lens."​
    Only if sensor/film size is held constant.
    2. "The captured area of the above scene (or image produced) varies depending on the format. More crop for DX less for MF"​
    Yes. This is basically the exception to the previous statement.
    3. "Adapting a 100mm Hassleblad MF lens to a DX body will capture exactly the same sized image as putting a DX lens on that same DX body."​
    Correct. The 100mm Hassy lens has a wider angle of view, but only when used with the larger film/sensor for which it is designed. A 100mm 4x5 lens will also have the same angle of view as a 100mm DX lens, as the 'limiting factor' is still sensor size.
    4. "It is a misconception to state that a DX sensor has more "pull" when using a 135 format lens"​
    True on paper, false in practice. As mentioned before, edge-to-edge sharpness generally improves, but the lens isn't any higher resolution. Also note that using a Hassy lens adds a LOT of air space, whic will probably produce more CA and internal flare than a DX lens.
    The moral of the story: if you own Hassy lenses and no good Nikkors, the adaptor might be a good idea. If you don't, you're better off buying Nikkors. I don't use my Hassy lenses on my DX Nikon for the same reasons mentioned above.
     
  16. Wow. This really isn't as difficult as people here are making it.
    As already stated, 100mm lens is a 100mm lens, no matter the format. Focal length is a property of the lens. What does matter, however, is the sensor/film format because that determines how much of the image circle is actually captured in the photo. In other words, smaller formats capture a smaller area of the image circle.
     
  17. ...no matter the format, focal length is a property of the lens. What does matter, however, is the sensor/film format because that determines how much of the image circle is actually captured in the photo. In other words, smaller formats capture a smaller area of the image circle.​
    Poetry! Well put!
    So, allow me to confuse things just a tad. If a larger sensor/film size simply captures more of the image circle, why then, is quality of the picture presumed to be better with the larger formats? I mean, this is why I bought my Hasselblad and my Leica...
     
  18. Image quality is greater, in that the image holds more detail, with larger formats only when you put the same scene in the frame the same way as you would do using a smaller format.<br>You can only get the same scene on a larger bit of film if you magnify the scene so that what fits a 35 mm format frame will fit, say, a 6x9 format frame the same way. You do that by using lenses with a longer focal length. Longer focal length = more magnification = less detail that is lost due to resolution limits of lens and film = better image.<br><br>Also, because there is more 'real estate' to accommodate a transition in tone, tonal transitions are smoother on larger formats.<br><br>All formats obviously need lenses that throw an image circle big enough to cover the frame. But no bigger. Making lenses that project bigger image circles than necessary is more expensive, and if focal length is kept constant, runs into the problems R.J. mentioned. So it's generally not done.<br>So it's not really just a case of a larger format simply capturing more of the image circle, but more of all formats capturing about all of the available image circle, with lenses made for larger formats also producing larger image circles.
     
  19. Martin,
    1. Set up a 35 mm camera with a 50 mm lens and an 8x10 with a 300 mm lens and take a photo from the same spot--film plane in the exact same spot. The two photos will be the same composition, but the aspect ratio will be slightly different. Nevertheless, basically you will have the same image, one captured on a piece of film 1x1.5 inches, or 1.5 square inches. The other will be captured on a piece of film 8x10 inches, or 80 square inches. Which one do you think will have more detail and better tone?
    2. Set up the two cameras and take the photo from the same spot with a 300mm lens on each camera. The 1x1.5 inches of the 35mm film will be the same as the center 1x1.5 inches of the 8x10 inch film. You should be able to lay the small negative directly on top of the big negative and have them line up. The 8x10 inch film will record much more than the center 1x1.5 inches of course.
     
  20. When the 35mm body looks through the MF lens, it only uses the center of the lens.​
    I see statements like this often, and I'm uncomfortable with them. It is more accurate to say that "it only uses the center of the image circle". Light rays arrive at the central region of the image circle (the area captured on a smaller format sensor) from nearly all parts (zones) of the glass, especially the front elements, and especially at longer than "normal" focal lengths. So using a smaller sensor is not like cutting cylinders through the lens elements, throwing away the outer perimeter (annulus) of all the glass, and just using "the center of the lens". In fact, the full diameter of the entrance pupil of the lens is always employed, regardless of how tight a sensor crop you take, because the entrance pupil diameter D defines the focal ratio f in conjunction with the focal length F (f = F/D). Since cropping doesn't change focal length, and doesn't change the image brightness, it cannot change the entrance pupil size either.
    Or look at it this way. When you stop down the aperture of a lens, you are indeed using only the central zones of the lens. This is the reason why stopping down reduces zone-dependent abberations like spherical and longitudinal chromatic. But does stopping down come with a shrinking of the image circle - do the corners go black? No; on the contrary, corner falloff tends to improve with stopping down. This proves 2 things:
    (1) The "center of the lens" doesn't just send light to the center of the image (aka the cropped sensor area); it sends light to the full image circle.
    (2) The outer zones of the lens send more light to the center of the image than to the edges. Stopping down is reducing the amount of light; you cannot make something brighter by taking light away; so if the corners now seem brighter with respect to the center, it's because it is the centre which has been worst hit by the loss of the light from the outer zones. A cropped sensor will therefore "see" those outer zones at wide apertures, just like the non-cropped sensor does.
    These outer zones aren't there to illuminate the outer zones of the image; they are there to improve the wide-open f-ratio mainly at the center of the image circle.
     
  21. Any Nikon 35mm prime will out-resolve any Hasselblad medium format prime, by design. As the image circle grows, the lpm resolution goes down. You do not get more detail from medium format, but you get more film resolution, which produces the illusion of more detail. Actually you are getting higher resolution gradations of gray (transitions from light to dark) with medium format than you are with 35mm film, purely because there is more film area to record it.
     
  22. Any Nikon 35mm prime will out-resolve any Hasselblad medium format prime​
    Sorry Dave, but I don't buy that one. I've done a lot of examination of my Hasselblad images vs. those with my Nikon and Leica's, and for the most part, I can't tell the difference for a given area of film.
    I know where you're going with this statement, but I think it is painted with a very wide brush, and needlessly discredits the quality of the Zeiss optics. Obviously, new lens technologies are showing up the older Zeiss designs (nano coating, widespread use of ASPH lenses, and new ED glass), etc., but given "period" lens comparisons, I think the Hasselblad lenses hold up.
     
  23. As mentioned before, they knew a thing or two about making good lenses back in the days before black and white television and the portable casette player. "New lens technologies" haven't brought much, if any, improvements. Just made it a bit easier to arrive at a result. But we may now have computers, back in the days before we did, people had time.<br>So don't assume so readily that new vs old will show old to be not as good as new. If you look up "new" in a dictionary, it probably (unless it's a rather "new" dictionary) does not list "better" among what it means.<br><br>Dave, your rather blanket statement lacks a basis in both fact and theory.
     
  24. Sorry, Dave, but Michael is right on this one. Here's data on the resolving ability of quite a few medium format lenses:
    http://www.hevanet.com/cperez/MF_testing.html
     
  25. "So, allow me to confuse things just a tad. If a larger sensor/film size simply captures more of the image circle, why then, is quality of the picture presumed to be better with the larger formats? I mean, this is why I bought my Hasselblad and my Leica..."
    Larger formats require less enlargement to produce the final image. Enlarge 35mm film to 8x10 and you're looking at close to a 10x enlargement (using multiple of the longest dimension, not area). Move to medium format and you only need to enlarge about 5x to make an 8x10 print.
     
  26. Martin
    As many have said the 100mm lens will be a 100mm lens angle of view on a full frame nikon and will have the 1.5 crop factor on a DX format. If you do go down this route consider a tilt / shift adaptor. I use a Mirex Tilt shift adaptor with Mamiya M645 lenses. This combination works very well (especially on full frame) and I get 35mm and above TS lenses for the price of an adaptor. The IQ is very high but I do need live view as they can be hard to focus and tilt.
    In terms of the oft cited lens resolution issue There may not be as much in it as people think. Here is a link that shows tests of 80mm lenses - the Mamiya 80 F1.9 and f2.8 do very well arguably out resolving the Leica 85 f1.4 and Nikon 85 F1.4. Even the Pentax MF lens out resolves the Nikon 85 F1.8.
    http://slrlensreview.com/web/benchmarks-resources-131/119-85mm-challenge/459-85mm-challenge-leica-vs-nikon-vs-mamiya-645-vs-pentax-645-part-2.html
     
  27. You want a 100mm manual lens on a Nikon, get a Series E 100mm f/2.8. It will cost next to nothing and you'll be surprised at how good the image quality will be.
     
  28. "As many have said the 100mm lens will be a 100mm lens angle of view on a full frame nikon and will have the 1.5 crop factor on a DX format."

    To avoid confusion: it will be a 100 mm lens on DX format (and any other format) too.
     
  29. The largest benefit to "new" lens technology, aside from AF speed, is not in the pro lenses, but the cheap ones. Nano coatings, etc. correct for colour and CA, but most "pro" grade lenses have very few issues with this anyway. For a very long time Nikon didn't even use ED glass on their top-level prime lenses that where 35-100mm because it 'wasn't necessary,' such as with the 85mm f/1.4D that performs VERY similarly to the G/ED/Nano nersion.
    The only place where there has been a huge improvement of non-AF performance over the last 20 years has been the cheap and/or kit lenses, where better coatings and better camera/lens chips allow lens makers to correct for uses caused by making lenses cheaply.
     
  30. The focal length of a MF lens, such as a Hassy 80mm (Zeiss) will change when adapted for a 35mm and/or DSLR (ACP-S). Even more so on an Olympus E-3. The 80mm equaled to that of a 200mm on the Olympus DSLR. This was verified with the viewing of a 70-300mm lens, tested corner to corner for sizing in the viewfinder. Also, this comes out to a magnification of 2.5x.
     
  31. Once again, the focal length remains what it is.
    When put on a 35 mm camera or a small-sensor DSLR, any medium format 80 mm lens produces the same image as any other 80 mm lens.
    If your test would show that it produces the same image as a 200 mm lens, either your test is seriously flawed, or you mix up things in the presentation of the test, or (very likely) that 200 mm you mention isn't 200 mm, but someone's made-up 'equivalent focal length'.
     
  32. Ken"MAX",
    You've bought into the common error of equating "crop factor" (using a smaller sensor/film) with "focal length multiplier" (increasing the focal length of the lens).
    The only way to actually increase the focal length of a lens is to add more glass - e.g. put a diverging lens behind it, like a teleconverter. Merely putting a lens on a smaller-sensored body does not add any more glass, so as Q.G. says, the focal length remains what it is. The only thing that changes is that you capture a smaller area of the image projected by the lens, and that smaller area corresponds to the field of view of a longer focal length lens. It is not, however, produced by a longer focal length lens! A real longer focal length lens would produce that same field of view - but over a much larger image area, with higher magnification (smaller angle per mm of sensor) and higher resolution.
    For example, that 80mm Hasselblad lens on a 645 medium format digital sensor (same 4:3 aspect ratio as the Olympus Four-Thirds sensor, so it's a valid comparison) gives the same image, in terms of field of view and composition, as a 25mm lens on an Olympus DSLR. The "crop factor" is 3.2x in this case, and if one were being tongue-in-cheek, one could say that "the Olympus lens has an effective focal length of 80mm, using 645 as a reference format". But the medium format setup will resolve 3.2x more detail in each axis, if the pixel sizes are equal (and they are almost identical in the 8.3 Mpix Olympus E300 and the 80 Mpix PhaseOne/Leaf medium format backs: 5.4 micron and 5.2 micron respectively); and the information content of the medium format image will be 10.3x higher than that of the Olympus! This should clearly illustrate that "effective focal lenght" is absolutely not the same as focal length. The Olympus 25mm lens is just a 25mm lens, and it cannot perform as anything other than a 25mm lens. By the same token. the Hasselblad 80mm lens is just an 80mm lens, and it cannot...well, I think you get the rest.
     
  33. Perhaps in one sentence:

    If you put a [FILL IN THE FORMAT OF YOUR CHOICE = a] lens of [FILL IN THE FOCAL LENGTH OF YOUR CHOICE = F] mm focal length on a [FILL IN ANOTHER, OR THE SAME, FORMAT OF YOUR CHOICE = a] camera, it produces the same image as a [F = THE FOCAL LENGTH YOU FILLED IN BEFORE] mm focal length lens made for that [FILL IN ANY FORMAT OF YOUR CHOICE = a] camera.

    Note that variable a is completely irrelevant (or a, a' and a'' if you are uncomfortable with using the same variable name for something that is completely irrelevant). You can fill in anything you like without it changing anything to the tautological essence of the above sentence, it being: F = F.
    From that tautology "it produces the same image" follows.
     

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