I understand the concept of image distortion at various focal lengths. Specifically, the facial distortion at wide angles and why you would want a short tele for portrait work. But I haven't seen anything that compares the facial distortion of a given FL lens from FF to APS-C. My gut feel is that a given FL will render similarly regardless of sensor size but I have nothing to back this up.
For reference, Stephen Eastwood has a comparison on his site of facial features at various focal lengths, but they're all based on FF sensors. http://stepheneastwood.com/tutorials/Tu … ective.htm
Those pictures, as labeled, are misleading to a degree. Although the information is true, what really causes (most of) the distortion is distance, not focal length. To fill up a frame with a face you need to be at different distances for different focal lengths, and that - the perspective distortion caused by being close, or apparent foreshortening caused by being far away, is what you are seeing in those shots.
There is also some degree of distortion inherent in the lens itself, and that will vary not only with focal length but with the particular make and model of lens. No general statement can be made about it that is universally applicable.
To answer your question as directly as I can, with an APS sensor you have to stand further from the model to fill the frame with the face than you would with a full frame camera. Consequently the predominant distortion effect you see will be caused by that change in distance.
A quick read on Barrel, Puncushion and Mustache distortion in lenses:
Lens Distortion Explained
The APSc sensors should have nothing to do with amount of distortion. I would imagine the focal length calculation and distance from lens would be calculated slightly different in the 1.6 range.
I recently bought the 16-35mm 2.8 lens from Canon... see here:
http://www.usa.canon.com/cusa/consumer/ … _8l_ii_usm
I read that this lens had very low distortion and have been pleasantly surprised. I edited up some images today from some interior shots of a condo and both horizontal and vertical lines had miniscule amount of barrel.
-looking over Stephen's shots, the images showing the most distortion are as you would assume the 35mm, 24mm and 19mm both shot extremely close to the subject.
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