IR exposure with my Phase One back

[mikeinlondon]

I recently got a Phase One P21+ back converted to IR but something very strange seems to happen when exposing..

The back will expose pretty much as normal without an R72 filter on the lens, but when I add the R72 (virtually opaque) it massively OVER exposes by consistently 6 stops!

How can this be? Can someone explain?

I created a support case but they seemed to think its normal.

I'm at a loss at how this can increase it by so much!

Regards

Mike

[Doug Peterson]

Using the same exposure or using auto metering?

Meters are almost always built to measure visible light. So by blocking visible light (R72 filter) the meter would push the camera to expose many stops more than it should if you're target is only IR light. You should expose manually and adjust based on the red channel of the histogram.

Your Phase One Dealer should be able to guide you through issues like this. Good ones will have spent the time (as we have) to learn niche applications like IR inside-and-out.
Doug Peterson (e-mail Me)
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