infrared focus correction

[Cameron Shaw <cameron@xxxxxxxxxxxxx>]

I found in focus tests with HIE and #25 filter, using Nikon F4 ( with non APO 
lens85mm f2 ) that the focus correction markings on the lens gave too much 
correction. Then I realised that focusing through the #25 red filter my eye was 
already making some correction.
So IMHO focus correction is too small to be needed in this situation. Maybe if 
the focus was first set with #25 and then a #87 filter was used some of the 
correction would have been made so with a reasonable depth of field no focus 
correction would be needed) Of course the halation effect softens the edges.

So my question is please, for non APO lenses what wavelength does the 
marked focus correction correspond to, xxx nm ?


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