Re: Reciprocity failure was: Re: How can I recognice 'old'

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On  3 Apr 97 at 11:09, JoePaduano@xxxxxxx wrote:

> Just a note-color infrared film does not require a focus shift, as the two
> color image layers record visible light.
>                                                      Joe Paduano
> 

Additional note: the infrared layer still requires a focus shift, as
it's IR-sensitivity is as high as with HIE. But since any focus
shift would cause problems with the other visible layers, it is not
a solution. The only thing you can do to get all colors back in
focus is stopping down (and perhaps set the lens between the visible
focus and IR-focus mark, to squeeze out the last % of sharpness), or
use a good (true) APO lens. Guenter Spitzing mentions in his book
that Ektachrome-IR images taken with an APO lens are significantly
sharper than with a normal lens. Probably most pronounced with tele
shots, where the benefit of APO shows only anyway. 

Note that stopping down is worse for IR than for visible light, as 
diffraction is twice as bad with 800nm as with 400nm. So don't overdo 
it....f8-11 should be the limit I guess.

I know some people disagree on this, but I have even seen this info
pop up in Russian(!) literature about IR-photography. I read it first 
in Guenter Spitzing's book though, in both his editions.




-- 
Bye,

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      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]

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