Re: Focusing IR

[mturner@xxxxxxxxxxxxxxx (Marc Turner)]

     >I must disagree here....:-))
     >One can very well look through #89B, at least for composition with 
     >wide angles. And since AF systems don't seem to have much trouble 
     >with focusing through an IR-filter (I even get focus locks through a 
     >very opaque #87C!), it might even work with teles (fast f2.8 lenses 
     >preferred of course, to squeeze out every bit of light for 
     >composition).
     
     This makes me wonder - if the autofocus system works through a 
     visually opaque IR filter, then it seems like it would be trying to 
     autofocus using only the IR end of the spectrum.  It seems like this 
     would automatically compensate for the different focus point and 
     handle the IR focus correction automatically!  Anyone have any insight 
     on this?  Does it work, or if not then why?  I have a lot of pain (as 
     I suppose others do) with these autofocus lenses that have no IR focus 
     marks.  Mostly I end up shooting with smaller aperture for DOF.
     
     -- Marc
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