DX vs FX: crop factor or no crop factor

Discussion in 'Nikon' started by azn137, Mar 28, 2009.

  1. Before I ask my question, I've read: http://www.luminous-landscape.com/tutorials/understanding-series/dslr-mag.shtml, http://www.digital-slr-guide.com/crop-factor.html and this http://digital-photography-school.com/crop-factor-explained

    I understand Nikon makes DX and FX lenses. DX's are for small sensor (crop factor 1.5) and FX's are for FF bodies. My question is, since the DX lenses will produce a smaller image circle, does it, then, have the crop factor?

    For example, the AF NIKKOR 50mm f/1.8D will produce a 35mm image circle, therefore, when I use it for my D80, I will get "75mm" instead. However, say, the AF-S DX Zoom-NIKKOR 18-135mm f/3.5-5.6G IF-ED , will produce a smaller image circle, do I get the 18-135mm view, or do I get 24-202.5mm?

    Sorry if my question was confusing. And thank you in advance.

    TN.
     
  2. Tam, the DX lenses are essentially optimized for the sensor. But the cropping is done at the sensor. So, yes, regardless of the focal length, it will still be cropped at when measured against a FF. This months Popular Photography has an excellent article on the subject.
     
  3. That means I will never be able to experience the true view of wide angle until I get a FX body :(

    On the same note, my assumption is the new Sigma 10-20mm F3.5 EX DC HSM (http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3360&navigator=6) has the same effect: I'd get the 15-30mm view compared to a FX body, even though the lens is designed for small sensors?

    Thanks for your input Mark.
     
  4. An 18mm DX lens and an 18mm FX lens will look the same on a DX sensor. They will both look like a 27mm lens will look on an FX camera.
    On an FX camera, an 18mm FX lens will look like an 18mm lens, and an 18mm DX lens will look like this (shot on film but it works the same), which I actually like:
    00Su4c-120149584.jpg
     
  5. I'm sure I'm not the first to ask this question: why the hell do they call it 18-135m, instead of 27-202.5mm then?

    Thanks guys btw, that cleared it up.
     
  6. Tam, it's all about sensor size, and the "industry" likes to compare any sensor that is not FF to the "effective" FF focal length.
    So yes, you're correct...an 18mm focal length on a DX sensor, is the "equivalent" of 27mm on a FF.
    This is one of the reasons why users of DX sensor cameras, such as myself, have 'ultra' wide-angle lenses, such as the 11-17 that I carry.
    I HIGHLY recommend that you read the article I referenced above, as it will help your understanding of what is going on with focal lenghts of the different sized sensors.
    Mark
     
  7. They call it that because the focal length is 18-135mm. The field of view is a function of focal length and film/sensor size. Focal length is a physical characteristic of the lens.
     
  8. Tam, Andew explained it the most simple. It's all about the sensor size. The focal length of the lens does not change if it's placed on a 4/3, DX or FX sensor camera. Only the output of your picture based on the crop-factor of the sensor.
     
  9. Thanks a bunch guys. It has been very helpful.
     
  10. If you use the same lens on different formats the field of view changes. The focal length does not change. Example: in DX a 33mm lens with give about the same 46 degree field of view (which is concidered a standard for as long as I can remember) as a 50mm gives in FX or film. In medium format 645 a 75mm lens gives about 46 degree field of view. In 6x6 its an 80mm which is also close in 6x7 format. I think a 150mm or 180mm is about normal for 4 inch by 5 inch format. All this is approx. depending on how the angle is measured but fairly close. IMHO its important to concider the prespective change that occurs when changing the focal length. If you want an ultra wide angle lens for DX look at the many zooms offered in the 10mm to 24mm range. You might have an easier time if you think about field of view. Greater than 64 degrees or so starts the wide angle range. I consider 90 degrees very wide.
     
  11. There is only one crop factor and that is the "angle of view crop factor". It is not practical to use angle of view crop as reference, since this value is not printed on lenses.
    Instead of "angle of view" crop factor it is more convenient to use "focal length" crop factor, but that measure is not exact and only a substitute to make it easy to explain.
    If you place a 50mm lens on DX format, it will limit angle of view to equivalent of a 75 mm lens on film or FX format.
    It is important to understand that the 50 mm lens will not magically become a felephoto 75 mm lens when you mount it on DX camera, since it will not bring subjects any closer as the real 75 telephoto lens would on film camera or DX camera.
    Some in camera viewfinder magnification can possibly introduce some view magnification factor that could appear as a telephpoto bringing objects closer.
     
  12. Nikon uses the actual focal length to specify both full-frame (FX) and DX lenses. The mount and distance from the film plane is the same and both fit and focus on the both types of cameras. The cropping factor is 1.5x, which is easy enough to apply. 35mm cameras have been around a long time, and people have become accustomed to thinking in terms of those focal lengths.
    P&S cameras usually specify the "equivalent" focal length. Their sensors come in different sizes, occasionally specified in the archaic terms of 1/2", 1/3", etc. A 1/3" sensor is not actually 1/3" across, so it's easier for the manufacturer to do the calculations for you.
     
  13. I think the industry just wanted to cause confusion that would never end. We have had formats of different sizes forever and I do not think that we ever had to deal with crop factors or did we....Photographers did however seem to shoot 35mm and medium format camera's for a long time before the digital world came about..People would think about it and figure that a 50mm lens on the 35mm was about the same as a 80 to 100mm lens on a medium format, (could that be a crop factor?). The crop factor term was not born yet but you can make a crop factor number between any 2 formats easily enough. It's based on the diagonal of the format..So the diagonal of 35mm film is 43.2mm and a typical medium format film camera was 6x6cm..The diagonal of the 6x6 in millimeters is 84.8mm. If you divide 84.8 by 43.2 then you find you have a crop factor of 1.96....Well then what is going on. Does the 35mm have a crop factor of 1.96x..Well yes it does if compared to a 6x6cm format camera. So then a 50mm lens on a 35mm is about equivalent to a 100mm lens on a 6x6 medium format.....Some people say the lens from a medium format does not fit the 35mm so this idea does not work but if you remember the medium format camera's many times would have a 35mm back so that you could shoot 35mm in a medium format camera..So there you go.
    Well if that is all clear as mud you can think of it this way. You snap the shutter and capture a pixel file in your camera the size of the sensor...The FX sensor is 1.5x larger then the DX sensor in a Nikon..Now you want to make a picture of 4x6in so you can look at it..The DX file must be increased in size 1.5x more then the FX file that was taken with the same lens in order to fill the 4x6 dimensions of the picture. Because the DX file is enlarged more it seems like there was a telephoto thing going on. But the answer is no there was no telephoto effect because you just enlarged your file 1.5x more from the DX sensor camera...Then the telephoto effect people talk about is not real telephoto effect or magnification but rather just increasing the picture size 1.5 times so that the picture is the same size from a DX camera and a FX camera when you view it on the computer or in a print form..
     
  14. Another way of looking at it:

    Take a picture on your DX body which already has a crop factor of 1.5, and crop it by keeping only half the original pixels.
    For example, from 12 Mp to 6 Mp. You will have another level of 1.5 crop factor. Your 50mm lens will be 50 x 1.5 x 1.5 =
    112.50. You will get a 112.5 mm telephoto lens for free.

    50mm is THE normal lens on FX or DX. It has the same magnification as the naked eye, that's why it'll always be normal.
    So 35mm is not the "new normal for DX". 35mm on DX just happens to have the same field-of-view as 50mm on FX.
     
  15. Adding to the confusion, some P&S cameras specify both the actual focal lengths and their equivalents in terms of the familiar 35mm film/24x36 paradigm.
    For example, Olympus describes my old C3040-Z P&S digicam zoom as both a 7.1mm-21.3mm (f/1.8-f/2.6) actual focal length zoom, which is printed on the lens, and its equivalent in the 35mm film paradigm, 35mm-105mm, which was printed on the box and peel-off label on the camera body. To someone unaware of the relationship between focal length and recording format size, a 7.1-21.3mm zoom sounds like an astonishingly wide angle zoom. But on the tiny sensor it's a very modest moderate wide to short telephoto. And, presumably (I can't find the specs offhand) the 1:5 relationship between actual and equivalent focal lengths translates to a sensor that is a mere 1/5th the size of the 24x36mm frame familiar to 35mm film and FX or "full frame" digital photographers.
    The industry assumes that dSLR buyers either already understand the relationships between actual focal lengths and recording media formats (just as they did with the Olympus half-frame 35mm cameras decades ago), or that novice dSLR buyers will eventually learn. And the manufacturers tend to assume that most buyers of P&S digital cameras don't know and don't care about such details and simply prefer to enjoy their cameras without being burdened by technicalities that aren't relevant to their enjoyment of photography.
    Besides, in 30-60 second TV ads, it's easier to hype megapixels than to educate consumers about these matters.
     
  16. 50mm is THE normal lens on FX or DX. It has the same magnification as the naked eye, that's why it'll always be normal. So 35mm is not the "new normal for DX". 35mm on DX just happens to have the same field-of-view as 50mm on FX.​
    It's true that if I hold my Minolta with a 50mm lens up to my eye and move the camera up and down I see only a slight change in magnification but that itself doesn't have anything to do with magnification of the final image - that depends on field of view and print size. You take a shot at 52.5mm on an FX and the same shot at 35mm on a DX and print them the same size and the 52.5 will have a slightly tighter depth of field but aside from that you'll get the same thing.
    Looking through the finder on the DX camera the image appears reduced. This is because the finder is smaller and it's displaying the same image.
     
  17. Tam,
    Of course you can play around with truly wide angles. My Tokina 11-16 is GREAT for this!
    [​IMG]
     
  18. The way I understand it is that the "Normal" lens for a camera system is based on the diagonal of the format and also on what the camera manufacturer specifies.
    So the 35mm(FX) format normal lens is actually 43mm but the manufacturer has decided to supply the 50mm lens as the normal. How that ever came about I cannot say because I don't know. Then we get to the DX format and the diagonal is 28mm and the manufacturer has decided to call the 35mm the normal.. I would agree that the 35mm should be the official normal because it does give similar results to the full frame FX 50mm lens but in both cases mathmatically the normal is actually 28mm (DX) and 43mm (FX). In the past many rangefinder were supplied with a fixed lens of 40mm which was based on the actual normal focal length...Many people liked the 40mm and I think a lot of rangefinders were sold because of the desirable fixed focal range.
     
  19. "That means I will never be able to experience the true view of wide angle until I get a FX body :("
    tam, there's a 'gotcha' here. if you look at the FX options for w/a vs. the DX options, you can see there are many DX wide lenses at reasonable prices vs. somewhat limited and/or expensive FF options. let's say you spend $3k on a d700 and another $1800 on a 14-24/2.8. that's almost five grand for "true" wide angle.
    OTOH, let's say you spend $650 on a new d200 and $500 on a sigma 10-20. your effective FL at the wide end is 15mm, only 1mm longer than the Fx set-up. so you will have spent almost $4k for exactly 1mm, and slightly better IQ which won't matter unless you are printing at huge sizes and/or pixel-peeping.
     
  20. That makes sense Eric :) I've never looked at it that way. And TBH, I don't plan on getting a FX body anytime soon, my budget is quite low for one.
     
  21. 14mm on D700 + 14-24/2.8 vs 15mm on D200 + Sigma 10-20. Interesting. An extra 1mm at $4k sounds expensive but the
    FX image is has much less noise and the lens has less distortion. This could be important for big printouts. Not important
    for most amateurs, though.
     
  22. " For example, the AF NIKKOR 50mm f/1.8D will produce a 35mm image circle, therefore, when I use it for my D80, I will get "75mm" instead. However, say, the AF-S DX Zoom-NIKKOR 18-135mm f/3.5-5.6G IF-ED , will produce a smaller image circle, do I get the 18-135mm view, or do I get 24-202.5mm? "
    Dear Tam. Probably, some one all ready said this. Your 18-135mm lens projecting an 18-135mm image to you small (1.5) DX sensor. The only different, you get a cropped image of the projected image, A 50mm lens projecting a 50mm image, unfortunately your DX sensor capturing the middle part of it not the whole image. The 50mm lens not going to be a 75mm lens. Different focal lens lenses has different perspective distortion. The projected distortion of a 14mm or a 200mm always 14mm or 200mm, on a Dx or FX. You just not geting the whole image on your smal DX sensor. 50mm is 50mm, 135 is 135mm all the time, and this is the hardest part for those whom do not no how the light travel trough the lens to the film or sensor plate. Go to K. Rockwell web site, and he explaining this with a picture, and diagram.
    The lenses designed for DX cameras still 50mm or 200mm, but the image circle smaller, fit only to the Small DX size cameras, and not usable for the FX full frame cameras.
     
  23. This months Popular Photo has a very good article on what format dslr is the best for the buck.
    I won't ruin the story for you but I will say its based on hundreds of their reviews on how the equipment tests told them what the best deal is.
    They have charts giving the pros and cons and they discuss the results of testing. I was surprised by some of what they had to say.
     

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