[MF3D.FORUM:1166] Re: Camera design

[Tom Hubin <thubin@xxxxxxxxx>]

Hello Richard,

> Tilting the film plane rather than the lens plane might be more
> mechanically complex, but it allows you to satisfy the Scheimpflug

Namedropper. ;)

> condition without requiring the lens to have an extended image circle
> (but the top and bottom of the image have slightly different
> magnifications - 

There are ways to tilt the film and make the magnification constant. I
think one way is to image 1:1. But that is not very useful to most
folks. 

The other is to use an afocal imaging system. That produces a constant
magnification, independent of object distance. A tilted object still
creates a tilted image but the magnification is constant. This still
meets the Scheimpflug condition.

By the way, the image tilt Beta is related to the object tilt Alpha by
the following equations:

M = -i/o = tan(beta)/tan(alpha)

rearranged:

beta = atan( M * tan(alpha) ) = atan( -i/o * tan(alpha) )

where: 
	M is lateral magnification
	o is the object distance
	i is the image distance
	alpha is the object tilt
	beta is the image tilt 

Why all this discussion of tilts? I must have ignored the original. Is
this to avoid using a pantoscopic lens or decentering the taking lens to
image a tall building without having the top of the building image
smaller than the bottom of the building?

Tom Hubin
thubin@xxxxxxxxx