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Forum: Pentax DSLR Discussion
09-13-2008, 02:12 AM
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For IR you are best off focusing in manual mode. Stop down your aperture too.
At different times of the day there is different amounts of IR light. You cannot see this light, so an auto focus sensor and your eyes can only see the visible spectrum of light. An auto focus camera will not focus properly with IR filters.
effective ISO drops too. For Rollei IR film the ISO drops from 400 to 3 with an R72 filter. For digital you might need to adjust your exposure index to compensate for the loss of light through an IR filter.
Different IR filters use and block different amounts of light in the spectrum, so results can vary there too.
experiment and take notes.
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