Anyone know what the difference is?
I understand the terms but they appear to do the same thing when adjusted.

Thanks..

Try this link:

http://www.planit3d.com/source/tutorial_files/poser7/3/p7cam1.html

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2714077

http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2796467

 Thanks Acadia... but unfortunately that does not explain the relationship between FOCAL and PERSPECTIVE.
I have a schooled background in photography so I understand what FOCAL length and Perspective is. I just don't understand their relationship in Poser.
Adjusting both controls seems to do the same thing.....????

They are identical - changing one changes the other.

I don't have any explanation why there are two. Only guesses.

OK.. this gem right out of the manual.

Focal: The Focal parameter dial sets the camera’s focal length. Smaller numbers give wider angles and will add more stretching and distortion as they decrease. Larger numbers give results like telephoto lenses, and result in less distorted but flatter images.

** Perspective**: The Perspective parameter shifts the current camera’s perspective without changing the camera’s location. This can give the illusion that the camera is farther or nearer to objects in your scene.

Seems to be the same thing.???? 
Spinning the dials causes them to both have the same values regardless of which dial one spins.
Must check to see if there is less barrel distortion when setting 19mm Perspective vs 19mm Focal.

I think adjusting the perspective too much in poser gives you an almost fish-eye lense effect and focal just zooms in or out..

Don't know if this is the same in later versions. In P6 Perspective is not the same as focal. The focal dial does what it says on the box, changes the focal length, and does not alter the POV. Perspective changes both the focal length, and the scale of the camera. I suspect that Perspective will change the POV for the Main and Aux camera (though probably not  the Dolly Camera), but have not done the tests to prove that theory.

I know that the manual says Perspective, will not change the POV, but I never trust the manual to give accurate or useful information. Perhaps it is correct, but I'll need proof before I believe it.

Quote - I know that the manual says Perspective, will not change the POV, but I never trust the manual to give accurate or useful information. Perhaps it is correct, but I'll need proof before I believe it.

Boy howdy, do I ever second THAT motion!

 This is what I see when adjusting the two dials FOCAL and PERSPECTIVE

Focal; zooms in and out, Perspective also changes and has the same value as Focal
Perspective; zooms in and out and Focal also changes to same value. However, Dolly X,Y and Z values change.
I see no visual difference in the preview window to indicate there is a change of optics except for the image zooming in and out.

Odd observation*:*
Set up the AUX Camera: select Right Hand Camera, turn AUX Camera Visibility ON.
Watch the Aux Camera move in and out (Z Axis)and change size when adjusting the Perspective dial ?????
Why does the physical size of the camera change?

 Just noticed that SCALE also changes when PERSPECTIVE is adjusted...!

Playing with the difference that Les pointed out (in P6 at least), it appears that this combination of the camera’s Scaling being linked with the change in the Perspective dial, allows you to somewhat simulates the cinematographers’ “dolly/zoom” move,  i.e. zooming-in while dollying back, or the reverse, to effectively keep the foreground subject the same size in the frame while causing the background to compress or expand behind them.    A well employed example of the disorienting effect this causes is the medium-closeup of Roy Scheider in Jaws when he first sees the size of the shark.
 
Dunno if that’s what they were really going for, but it seems to work pretty well with longish lens lengths.

 hi folks,

things may clear up when you put two objects at different distances to the camera. In P8, say Andy and a ball, at 1 m up, 2 forward, 1 mtr aside.

Zoom will bring both closer or further away, focal distances stays the same and the image flattens while zooming. Just like an ordenairy lens.

Perspective will mainly effect the further object, the closer one will stays in place, more or less. This lets you change depth in the image. It does so by scaling the camera, relative to 0,0,0. This makes it move (dolly) as well as grow / shrink. As a result, the focal distance changes, so watch out when deploying DoF as well. 

In the end, there is one camera with one perspective and one focal length. That why they're the same. You can scale the camera separately too, with similar effects. 

In other words: if you halve the focal length, double the dolly and halve the scale, you will get the same result as just halving the perspective. It's a three-in-one action, for your convenience. Or confusion. It gives you zoom-with-depth, as in standing closeby, instead of zoom-with-flattening as in using a long lens.

Regards

Please note that if you are one of those people who are trying out the Luxpose exporter to Luxrender (or considering it), Luxrender does not understand it if you scale your camera over 100%. I was having a problem with this initially on export.  The scene in Lux would come in super zoomed, not at all what I had for preview before export. Then I was alerted to this scaling thing and checked my main camera. Somewhere along the way with some preset my main camera had been scaled to 264% and this is why Luxrender was giving me a super zoomed in image. So scaling the camera is only a problem if you want to go to Luxrender.