I am a 3D animation interactive developer working on a project where a gesigner will be able to place a computer-generated object and place it interactively into a still photo.
In order to do this, I need to generate a value (field of view) that is used in the synthetic 3D scene. This value is derrived from a formula based on film back size and focal length.
I have experimented with several formulas and they all resemble this:
Field of View = 4 * arcsine ( frameSize/( focal length * 4))
Well, the basic formula (subject to some provisos) is:
A = 2 arctan (d/2f)
where A is the field of view, as an angle (in your choice of direction: vertical, horizontal, or diagonal), d is the corresponding dimension of the frame, and f is of course the focal length (d and f in the same units).
That all assumes focus at a distance that is substantial compared to the focal length.
However, I seem to be missing something. as I plug in frame sizes for various film backs like the P45 49.1mm x 26.8mm , the resulting view needs to be scaled up or down..similar to a digital multiplier or crop factor? (i'm reading these terms from various internet articles so I may be using the terms wrong). It seems like the formula works for *film* back sizes and needs some sort of additional factor to compensate for image sensor sizes
Nothing of that sort is involved if the applicable quantities are put into the formula.
Note that the focal length is the focal length, not some "equivalent" focal length.
The problem is presumably with your formula, which is incorrect. (Sorry!)
Does anyone have any knowledge of crop factors or digital multiplers in DSLR backs like the P21, P25, P30, P45 and even other filmbacks like Leaf Aptus, HaselBlad, Canon EOS-1D Mark2?
Do you want these in order to compare the behavior of various things on those backs with things as they would work on a full-frame 35-mm camera? Or do you want to compare the behavior of things on those backs with the behavior of an 8x10 camera? Or what?
You are really best off not to fool with those notions, and describe the behavior of various things on those backs in terms of their behavior with those backs.
No relative format size factor (by whataver name) is needed for any actual optical calculations. (The laws of optics have no idea what format size some people have adopted as "the real thing". Gauss and Newton had never used a full-frame 35-mm camera.)