Response to IR focusing formula

George, you brought up a good point. I mean a slightly shorter distance. That would require a slightly longer bellows. Try looking at a lens for a 35mm camera. It might have the red infrared focusing mark. If it does you will get a good graphic on what to do.BTW, I work in infrared in 35mm. I use a 24mm lens at f8 and use the hyperfocal distance for my focus setting. That might give you a direction to go in for your large format work.

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