Saturday, 10 December 2016

focal length - Does sensor size affect lens distortion?


There was recently a video posted about how different focal lengths affect portrait photography, specifically how distortion at smaller focal lengths have more distortion and are less flattering.


So the question is that, because we always talk about how Canon's cropped sensors have a 1.6x crop factor so the lenses are essentially longer, does the distortion caused by the lens change when used on a cropped sensor?


My initial thought is "no" given that my idea of how a cropped sensor works is like printing off a 8x10 picture and then cutting out the 4x6 that I like: the picture doesn't change, only my view of it.


However, if distortion is least prominent at the center of the photo and most prominent at the edges, then the perception of the net effect of the distortion would be changed by using a cropped sensor and I get confused again.


Any thoughts?



Answer



What changes is perspective. It's not lens distortion (barrel distortion) that makes wide-angle closeups unflattering, it's how close you need to get to the subject to fill the frame. For a given focal length lens, you need to be closer to fill the frame using a full-frame camera than you do with a crop-sensor camera. That means that, proportionally, the nose, say, is going to be much nearer the camera than the eyes with a full frame than with a crop sensor, and the ears will be off in the (comparatively) far distance.


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