Monday, 16 April 2018

lens - When I use FX lenses on a DX camera, does the focal length or minimum aperture change?


If I put a Nikkor 35mm f/2 FX lens on a DX camera, is it still 35mm f/2, or has the effective focal length or minimum aperture changed, because it is being used on a smaller format than what it was designed for?




Answer



Aperture is unaffected.


The field of view becomes 35mm x (the crop factor of your sensor), which is 1.5 in the case of Nikon DX cameras (It's also 1.5 for Pentax and Sony, 1.6 for Canon and 2 for Panasonic & Olympus).


So your 35mm Nikon lens has a 35mm x 1.5 = 52.5mm "35mm equivalent" field of view.


Note that the perspective doesn't change, just the amount of 'stuff' you can fit in the frame. The image will still look like a 35mm image as shot on a full-frame sensor, but with the sides cropped in to give you the field of view of a 52.5mm lens on a full-frame sensor.


(Most people round that to 50mm "35mm equivalent" field of view, regardless of 1.5 or 1.6 crop factor)


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