Yup - assuming you're basing your focal length on a 35mm camera equivalent, as most photographers still do even when using a camera with a different sensor size - Poser's cameras' focal lengths are 0.7x that. 

In other words, to get a field of view similar to a 35mm film camera with a 50mm lens, set your Poser camera to 50 x 0.7 = 35mm focal length.

Citation: Bagginsbill says so here and here, and elsewhere too. ;)

(I have reason to believe the exact value might be the reciprocal of root 2).