Subject: Re: Scaling the Camera Problem
Date: Tue, 31 May 94 2:05:23 EDT
From: jgoldman@acs.bu.edu (Jeffrey Goldman)

> 
>   I'm not clear on the use of the "P" (POV?) vs. the Zoom button in the
> perspective window. Can you possibly summarize the difference, and when one
> would use P? Having a wireframe cow eyeball me from my monitor wasn't terribly

> informative.

	(Z)oom would change the focal length of your camera while (P)?
would change the point of view per se...
	For instance, put an object in the Stage Editor and track the
camera to it. Turn on Camera Lines. You now get a cone representing
the camera's field of vision. 
	You'll notice that using "Z" zooms the 'lens' in and out while
retaining the same camera position (ie. the camera itself never
moves). The larger end of the cone moves back and forth. Essentially
you're changing the focal length of the lens...
	If you use "P" you'll notice that the physical location of the
camera will change yet the frame stays the same. As you move "P" one
way your camera moves closer to its frame thereby decreasing the focal
length of the lens. If you move "P" the other direction the camera
will physically move away from the object (while retaining frame size)
thereby increasing the focal length. The effect is akin to dollying in
and out while keeping the frame the same by relatively changing focal
lengths.
	My technical description will probably be way off now. You may
see the effect in commercials or 'dream/wierd' sequences in movies.
What happens is that the object on or near the focal plane (the
base/end of the field of vision cone/pyramid) will stay relatively the
same size while the amount of background will increase and decrease.
	Say you shoot a beachball with a wide angle (28mm) lens. The
beachball fills %50 of the frame. Physically take the camera and move
it 100 feet away. With the wide angle lens the beachball now seems to
occupy substantially less of the frame (perhaps %5). If you use a
telephoto lens (210mm) you are now 'zoomed' in on the beachball. The
beachball will once again occupy %50 of the frame even though the
camera is 100 feet away from its original position. This is what "P"
does in Imagine. The result is that with a 28mm lens you have much
more depth of field as compared to a 210mm lens. Using "P" makes it
easy to increase of decrease the DOF of a scene...
	Hope that when you wake up after that longer than necessary
explanation it helps... :-)

							J.---->

E-Mail: jgoldman@acs.bu.edu



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