[Leica] Image circle

[mark at rabinergroup.com (Mark Rabiner)]

> Richard,
> 
> The size of a lens image circle is not absolute but depends on your
> criteria. Most lenses are sharp and relatively distortionless in the
> center of the image. Quality and illumination fall off as you move
> away from the axis. You have reached the edge of the lens image circle
> when the image quality no longer meets your photographic requirements.
> That being said, the easiest way to determine the approximate size of
> the image circle is to hold the lens in front of a ground glass. Adjust
> it so that it focuses a distant scene and simply measure the
> illuminated circle on the ground glass. Most normal lenses have a
> reasonable quality of image in a circle with a diameter approximating
> their focal
> length. Symmetrical lens designs tend to have a bigger image circle and
> are frequently used for wide angle lenses.
> Larry Z
> 


And your image circle gets better when you work closer.
That you learn from view camera work.

[Rabs]
Mark William Rabiner