Auto-focusing and IR focus shift

[Daniel Cardish <dcardish@xxxxxxxxxxxxx>]

When I used to use my old Minolta 9000 with IR film, I found that the camera
had no problem focusing and giving me a valid meter reading with a B+W #92
filter (similar, I believe to a Wratten 89B) on the lens, even though the
filter is almost opaque (in sunlight I can just manage to see the outlines
of some subjects, but too dark to focus by eye).

Not only that, but the camera seemed to adjust the focus point for the lens
with the filter in place.  I think that since the autofocus system is
sensitive to IR light, then if I allow only IR light to pass through the
lens, then the focus shift should be handled automatically.

In any case, I never had problems getting properly exposed and focused
negatives.  I use an EI of about 1000 metering through the filter.

Has anyone else noticed the same with their autofocus cameras?



Dan Cardish  
<dcardish@xxxxxxxxxxxxx>

<http://www.spherenet.com/dcardish/photo.htm>
        


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Topic No. 20