Sharpness at infinity

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Jamie writes:

>After seeing the pictures taken by (Kodak's) new owner, with the 
>lenses freshly calibrated, I was shocked by the sharpness, especially 
>at infinity (I find most vintage stereo camera fail in this regard).

I was just reading the book "The INs and OUTs of FOCUS" by Harold
M. Merklinger.  The author makes a few valid points.  For example,
he states "If we want _anything_ at infinity to be critically sharp,
focus at _infinity_".

Dealing with stereo photography and learning about depth of focus
and hyperfocal distances, has made us afraid to focus at infinity.
We feel that focusing at infinity is a waste of focusing range.
So, we do crazy things like focus at the "hyperfocal distance" of
15 feet at f11, even though there is nothing closer to the
camera than 20 feet.

Many times the smallest things that we want to resolve well 
are found at infintity.  Closer by objects are larger and easily
recognizable and do not have the same sharpness requirements as
objects at infinity.  "Since working out these details", says the
author, who does a lot of scenic photography, "I find I do a lot 
of photography with the lens simply focused at infinity."

Back to Jamie's remark, I suspect that the lack of sharpness at 
infinity seen in pictures from vintage stereo cameras is due
to not focusing at infinity.  Another factor might be that the
camera needs ajustment (the calibration that the Kodak went 
through) to correct focusing so that the image at infinity is 
sharp when the lens is focused at infinity.

-- George Themelis


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