IR Focusing and Diffraction

[rsage@xxxxxxxxxxxxxxxxxxxx]

First of all. Thanks to Russ for info on Abbey Camera. I just placed an
order.
Second. As there has been talk of focusing, this is from FAQ:
>>"Since the Konica film sensitivity is nearer visible light than the
Kodak, IR marks for the Konica film are about halfway
     between the standard IR mark on your lens and normal.

     To improve apparent sharpness use a small aperture to increase
depth of field.

     Another note: don't stop down too far! Diffraction is twice as bad
with long IR waves as it is with visible light!
     Stopping down to minimum aperture is a NO NO! " <<


I would guess that the focusing would all depend on the filters used.

Could someone explain the problem with diffraction at small apertures?
This says to stop down, but not too far. What is too far? If a view
camera lens stops to f45, is it OK to go to f32? I was thinking of
trying some IR pinhole photos at about f128. What can I expect? I've
heard of the "circle of confusion", but this is confusing.

Rod Sage

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