IR focus distance

[Tom Harrison <tomh@xxxxxxxxxx>]

Craig wrote
> Anyway... if anyone has any more great tips for exposure outside using =
> Kodak HIE with a Red 25 filter I would like to hear from them.  Why do I =
> have to shoot at f/8 or f/11 or 16?   Is this something to do with the =
> different focusing plane of IR?   I am using a Canon L series lens which =
> is Apochromatic and should therefore focus the infrared on the same =
> plane as visible lightwaves, so do I still need to adjust the focus or =
> follow the guidelines for using f stops? Besides the Canon lens doesn't =
> have an IR index mark on the barrel!!!

Unless the lense manual specifically says that infrared focus is the
same
as visible focus, you should not assume so, no matter what it's called.
Some lenses don't have an IR index mark because the manufacturer didn't
think it was important.

- -- 
Tom Harrison
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End of Infrared-Digest V0 #573
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