A good friend and I were recently discussing the effects of front tilt upon 'film plain.'
In connection, my friend said he didn't understand why, for example, the image projected onto a motion picture screen by an m.p. projector (and lens) was able to be in focus across the projected image plain. After all, he cited, the screen is 'tilted' relative to the film plain. IOW, the projection lens is (usually) higher than the screen - and so must be tiled downward to correctly project its image to the screen.
I was not able to explain 'optically,' I realized, how or why the projected image could remain sharp across the plain of the screen. Related to 'depth of field,' or 'depth of focus' considerations?
What is the simple 'optical' explanation?