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  1. #1
    Senior Member

    FX Lenses on D7500

    I have a Nikon DSLR with two kit lenses (18-55 f/3.5-5.6 & 70-300 f/4.5-6.3). I also have two Nikon Series E lenses that were used on a Nikon FM film camera. Both of those have a lower maximum f stop (35mm f/2.5, 50mmf/1.8) and might be good for low light situations. I wanted to see if these would work on my D7500. I realize I would have to focus manually, set aperture manually (both of those on the lens), and also meter manually for setting shutter speed (on the camera).

    So I experimented. With my camera on a tripod took four shots (all at same distance from subject):
    1. With my 18-55mm lens set at ~35mm, in A mode - f/5.6, 1/160, ISO 800
    2. With my 18-55mm lens set at ~50mm, in A mode - f/5.6, 1/160, ISO 800
    3. With the Series E 35mm lens, in M mode - manually set f/5.6, 1/160, camera set ISO 800
    4. With the Series E 50mm lens, in M mode - manually set f/5.6, 1/160, camera set ISO 800
    (#2 & 3 only worked in M mode.)

    I had expected that since the Series E lenses were basically FX lenses that the prime 35mm lens would act like a focal length of ~50mm and the prime 50mm lens would act like a focal length of 75mm on a DX camera.

    BUT the object size and angle of view of the picture taken with the Prime 35mm lens was identical to that of the 18-55mm lens @35mm. And the same for the pictures of the Prime 50mm and the 18-55 @50mm. Shouldn't the pictures taken with the prime lenses have shown a different sized image (telephoto-ish) comparatively to the DX images respectively?


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  2. #2
    Senior Member
    480sparky's Avatar

    Re: FX Lenses on D7500

    Once again, "Crop Factor Multiplier Confusion" rears it's ugly head.

    Here's the truth of the matter: Focal length is focal length. NOTHING about it changes between FX and DX. 35mm is 35mm. 50mm is 50mm. 200mm is 200mm. Format (FX/DX) does not affect focal length one tiny bit.
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  3. #3
    Staff
    Super Mod
    Don Kuykendall's Avatar

    Re: FX Lenses on D7500

    Quote Originally Posted by 480sparky View Post
    Once again, "Crop Factor Multiplier Confusion" rears it's ugly head.

    Here's the truth of the matter: Focal length is focal length. NOTHING about it changes between FX and DX. 35mm is 35mm. 50mm is 50mm. 200mm is 200mm. Format (FX/DX) does not affect focal length one tiny bit.
    The difference comes in when you try to compare that 35mm lens on the DX camera and the FX camera. the apparent focal length would be different at that time.

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    D750***D7100***24-120 f/4 ***70-300***Tamron 150-600***Tokina 16-28 f2.8***50mm f/1.8***Photoshop/Lightroom CC

  4. #4
    Senior Member

    Re: FX Lenses on D7500

    A dx sensor is smaller than an FX sensor. The dx sensor does not capture the entire image that is cast onto the film plane. That smaller captured area ends up getting enlarged to a standard size, hence the apparent zoom or crop factor. So on a dx camera it makes no difference if you use a dx or fx lens. Compare this to a 35mm negative, get the 35mm negative printed at 5x7. Then take that negative and trim 1/8" off each side. Print the resulting cropped negative again at 5x7. That's the DX concept. I guessed at the 1/8" but you should get the idea: Less image captured, but its enlarged to fit the same paper size that you printed the full size negative on.

    Now for the lens... Either fx or dx lens will work on dx. The difference is the dx lens is a cheaper design. They 'cut corners', figuratively and literally. The outer edges of the cast image won't be captured by the smaller sensor so the dx lens can be designed cheaper and lighter. The image that spills beyond the sensor does not have to be good. But put that dx lens on an fx sensor and you might get an image with distortion at the edges and corners. Or maybe vignetting. Or you may get away with it and not see any noticeable problems.
    I must have a really good camera.

  5. #5
    Happy to be Canadian
    Super Mod
    Marcel's Avatar

    Re: FX Lenses on D7500

    Your prime lenses (if they are AI-S) should meter with your camera, but I think only in A mode. But you have to put the lens aperture at it's smallest aperture (read larger number) and go in the menu to let the camera know what is the largest aperture of that lens.
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  6. #6
    Senior Member
    480sparky's Avatar

    Re: FX Lenses on D7500

    Quote Originally Posted by Don Kuykendall View Post
    The difference comes in when you try to compare that 35mm lens on the DX camera and the FX camera. the apparent focal length would be different at that time.
    Once again, the focal length DOES NOT CHANGE. A 35mm DX lens is 35mm. A 35mm FX lens is 35mm.

    What changes is apparent FIELD OF VIEW between a 35mm lens on a DX body and a 35mm on an FX body.
    Don't mind me... I'm out roaming around somewhere between Zone III and VII.


    Go forth and actuate!


    My Website.

  7. #7
    Staff
    Super Mod
    Don Kuykendall's Avatar

    Re: FX Lenses on D7500

    Quote Originally Posted by 480sparky View Post
    Once again, the focal length DOES NOT CHANGE. A 35mm DX lens is 35mm. A 35mm FX lens is 35mm.

    What changes is apparent FIELD OF VIEW between a 35mm lens on a DX body and a 35mm on an FX body.
    That is why I said "apparent focal length "

    ================================================== ============================
    D750***D7100***24-120 f/4 ***70-300***Tamron 150-600***Tokina 16-28 f2.8***50mm f/1.8***Photoshop/Lightroom CC

  8. #8
    Senior Member
    480sparky's Avatar

    Re: FX Lenses on D7500

    Quote Originally Posted by Don Kuykendall View Post
    That is why I said "apparent focal length "
    Hence, the continued confusion. A better term would be "equivalent field of view".
    Last edited by 480sparky; 01-25-2018 at 12:02 AM.
    Don't mind me... I'm out roaming around somewhere between Zone III and VII.


    Go forth and actuate!


    My Website.





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