[LargeFormat] Goerz Artars

[Alan Davenport]

At 06:17 AM 5/27/2002 -0400, you wrote:
>Michael, you had a formula for working out coverage, but I didn't quite
>understand.  What is the "theta" of a lens?  Is this information easy to
>find for any lens?  Then in the formual D = 2 f tan (theta / 2), is it a
>straight multiplication of all factors?

Theta isn't exactly gobbledegook; it's the angular dimension of the
cone of light rays from the lens to the focal plane.
(Theta / 2) then gives you the angle of the outside rays normal to
the film plane.  The tangent of that angle, multiplied by the focal
length of the lens ("f") gives the radius of the image circle in whatever
units you used for the focal length.  Lastly, multiplying the radius
by 2 gives the diameter of the circle, D.