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audiomystery · Posted: Sun Oct 02, 2005 7:37 pm Post subject:

I am sure this has come up before but I can't seem to find a comparison of us exposure numbers and the f/stop equivalents. If someone could point me in the right direction I would be most appreciative.

78ltd · Joined: 04 Sep 2005 Posts: 62 Location: Texas

U.S. 2 is F/4
U.S. 4 is F/8
U.S. 8 is F/11
U.S. 16 is f/16
U.S. 32 is F/22
U.S. 64 is F/32

If you have a Dagor U.S. 2.9 is F/6.8

Les · Joined: 09 May 2001 Posts: 2682 Location: Detroit, MI

It's a hard subject to Google, US can mean many things and even if you knew that it really meant Uniform Scale it doesn't help.

there is a wonderfully complex formula but everybody remembers that f16 and US 16 are the same. After that I count on my fingers, unlike my slide rule, they are always with me in the field.

See also

http://www.sizes.com/tools/photoaper.htm

audiomystery · Posted: Mon Oct 03, 2005 3:31 pm Post subject:

you have no idea how much I appreciate this. I have been so wrong on the exposures. Thanks.

78ltd · Joined: 04 Sep 2005 Posts: 62 Location: Texas

You ought to try using a lens marked in Stolze numbers. I have a early Dagor in a sunk focusing mount with that system.
F/6.8 is 4.6 and F/16 is 24 and F/32 is 96!