APS-C effect on FF lenses

Started 11 months ago | Discussions thread
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Jonathan Brady
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APS-C effect on FF lenses
11 months ago

On the EOS M forum, a user claimed that the PERSPECTIVE distortion stays the same for a lens when mounted on an APS-C camera and that the only difference is that the image is cropped.

I've never thought about this before because many people say things like "your 50mm lens will behave like an 86mm lens" so I always assumed that the perspective distortion was a part of that.  However, what that poster said makes a LOT of sense - you're LITERALLY just cropping the photo when using an APS-C camera, you're not changing the characteristics of the lens.  A 50mm lens is still a 50mm lens, the resulting image is just cropped because the ANGLE of view changes.

So, if this is the case (and I'm coming to terms with the notion that it probably is - it makes sense), then a 35mm lens on APS-C really ISN'T a substitute for a 50-ish mm lens on FF (ie, for portraits) as the perspective is skewed and the portraits may be distorted.  Similarly, a 50mm lens isn't a substitute for an 85mm lens and an 85mm lens isn't a substitute for a 135mm lens.  They are great substitutes if you ONLY care about the angle of view (aka: crop factor) but if you're looking for the proper perspective, they're not, right?

The other aspect to this is framing... to achieve identical framing using a 50mm lens on FF and also a 50mm lens on APS-C, you'll have to stand further away from your subject when using the 50mm on an APS-C.  Does the distance to the subject change the perspective distortion and make the same lens on 2 different format bodies equal?  As I'm wrapping my mind around all of this, I don't believe it does but I wanted to ask and be sure.

Thanks for any help/insight!

 Jonathan Brady's gear list:Jonathan Brady's gear list
Canon EOS M Canon EOS 6D Canon EOS 70D Canon EF 50mm f/1.4 USM Canon EF 85mm f/1.8 USM +16 more
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