IR focus correction is possible with AF cameras

[Rolland Elliott <rolland_elliott@xxxxxxxxx>]

Found the following post in the Nikon Digest, which is very
interesting.  By taping an IR gel like the 87 or 87C over the camera's
autofocus sensor's it looks like it is very possible to get an AF SLR
camera to auto focus in the IR region.  If it works, it would open the
doors to easy focus compensation in IR photography using wide
aperatures.

"Curfman, Donald (GEIS)"
<Donald.Curfman@xxxxxxxxxxx>

	> If I use a true IR filter that lets in 
	>>  no visible light, will the camera still
	>> be able to focus on the IR spectrum?
	> I'll try it tonight when I get home and 
	> let you know what happens.  I bet it'll work.
	
I taped a small piece of 87C gel over the AF sensors
in the bottom of the F5's mirror box, and taped another
piece between the film rails inside the back (between 
the shutter and the film), and loaded up a roll ofKodak HIE.
It appears to be working.  I haven't developed the film yet, but the
camera focuses approximately the right amount in front of the visible
light image.  
I was using a 105mm/f2 DC to test it out.  I figured 
it's narrow depth of field would provide a good test of focusing
accuracy.  
Even with an f2 lens, it takes a lot of IR to autofocus.  
With the subject in direct sunlight it focused pretty 
well, but any amount of cloud cover reduced the IR 
enough to prevent the AF from working at all. 

Hope you found the above interesting
Peace Rolland



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