Quote Originally Posted by Grainy View Post
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Do I understand you correct that if I use this method each time for this pinholecamera I can just multiply my lightmeter reading @iso5 f/22 with 100?
Assuming your f-stop equivalent is f/220, yes. But I was just guessing a typical number. Joe VanCleave in the post above has shown you the accurate way to do the math, and pointed out some possible pitfalls re: tungsten lighting. The smallest f-stop I can set on my Gossen Digisix is f/32, the meter has a ring you set and then read off combinations of shutter speed and f-stop. Using f/22 and a multiplier is just a handy way of extending that scale to the teeny tiny apertures.

In my first response at the beginning of this thread I posted two links that get you to a bunch of information about all sorts of pinhole considerations.