Is the difference between a good 50mm vs 85mm lens just your distance from the subject?

Question

I was wondering: is the difference between a 50mm f/1.8 lens and a 85mm f/1.8 lens just your distance from the subject? Let's assume that distortion is minimal; both lenses are of high quality. Does that mean I could take a step or two back or forward and use only one lens?

Note that I'm looking for scientific answers.

Answer

Perspective is a function of distance, not the angle of view of the lens. You could crop an image taken with a 50mm lens and get the same result as using an 85mm lens, but walking closer with the 50mm would give your shot a different perspective.

The whole scientific answer I'm not qualified to give, but there is a Wikipedia page on this subject: http://en.wikipedia.org/wiki/Perspective_distortion_(photography)

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