old U.S. stops vs. stanard f/stops

[Clark Savage Jr.]

I have several old lenses mounted in Kodak ball bearing shutters that date from around 1916. The callibrations are in U.S. stops. How do these relate to modern f/stops?

[Bill Hahn]

See this thread (which I found by typeing "US fstops" into a google search):

http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=000P49

[John H. Henderson]

Actually, according to Kingslake (History of the Photographic Lens), U.S. stands for "Uniform Scale" and is N*N/16, where N is the f-number.

The beauty of this system is that doubling the U.S. number halves the exposure, instead of the f-number system in which multiplying the f-number by the square root of two halves the exposure.