Poser's virtual film is 25.4 mm wide. (1 inch) In traditional 35mm film cameras, the image frame in landscape mode is 36 mm wide. This is roughly (but not exactly) the "crop" you find in APS-C cameras, by coincidence, not design. So the view you get in Poser is much closer to that of a modern cropped-format DSLR vs. the "full frame" which refers to a 36mm sensor.

Poser's virtual film height is variable, while real film is always 24mm in height. (When used in landscape mode) Real film aspect ratio is always 3:2, where Poser's is anything you want. But for purposes of matching field of view and perspective distortion of a real camera, we just need to consider the sensor width.

You can calculate the comparable full-frame field of view using ratios. The ratio 36 / 25.4 is about 1.4173. So in Poser, the 50mm setting would produce an image roughly the same as a full-frame 50 * 1.4173, or about 70.8 mm in real-life full frame.

Go the other way by division. Suppose you want to match a full-frame 50mm field of view -- so you use 50 / 1.4173 = 35.27 mm in your Poser Focal parameter and that will match.

To match a portrait viewpoint, things get tricky. I will forego an explanation of that.

When you ask about movie makers, now you're completely in lala land. Movie makers use "anisotropic" lenses which squeeze a panoramic image into a rectangle on the film of just 24 x 18 mm. Projectors reverse the squeeze for display. I don't think you really mean to match the images on an anisotropic lens, so it isn't worth examining.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)