Don, re your post number 12.
I think you are talking about the compression of planes that you get with long lenses. This is known as ariel perspective. But perspectve as I was using the term relates to the size of objects relative to each other. Christine's pictures illustrate this admirably. Or have I misunderstood you. What I was trying to give was a mathematical knock down proof that the relative size of objects in a picture depends only on subject distance and not at all on focal length. That is why I looked at the ratio ha/hb.
John
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