Re: f/32 testing

[T3D john bercovitz <bercov@xxxxxxxxxxx>]

Greg Erker writes:

>    The diffraction problem is caused by the physical size
> (diameter) of the hole not the f-number (which is a ratio).

This is correct but since it's a point that confuses a lot
of people, allow me to expand on your post.  The _angular_
resolution depends on the linear aperture ("the physical size
(diameter) of the hole"), not the relative aperture.  And
_angular_ resolution is exactly what we care about in stereo
photography because we always try to view from the center of
perspective.

_However_, it is also true that the _plate_ resolution is only
dependent on the f/number (relative aperture) of the lens and
not on the linear aperture of the lens.  That fact doesn't
concern us here.  So don't be misled.

In formulas:

angular resolution in seconds of arc ~= 100/ linear aperture in mm

plate resolution in lines per mm ~= 1600/ (f/number)

John B


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