That's definitely on the right track, but not quite completely
correct. Nearly all interim f-stops are on 1/3 stop increments, not 1/4
stop increments. f/1.2 is one of the exceptions . . . 1/2-stop faster than
f/1.4.
Some common lens speeds at other than full stops:
f/1.2: 1/2-stop faster than f/1.4
f/1.7: 1/2-stop faster than f/2
f/1.8: 1/3-stop faster than f/2
f/3.5: 1/3-stop faster than f/4
f/4.5: 1/3-stop slower than f/4
f/6.3: 1/3-stop slower than f/5.6
These all taken from my Weston meters (1/3-stop: Master V; 1/2-stop: Ranger
9) and confirmed by my math regarding 1/3-stop and 1/2-stop increments. In
general, f-stops and film speeds run in 1/3-stop increments.
-- John
At 16:43 3/31/03, Moose wrote:
The simple math is that 1/4 stop increments (to more decimal places than
have any possible practical meaning) from f1 to f2 are
1.000
1.069
1.155
1.265
1.414 (sqrt of 2)
1.512
1.633
1.789
2.000
As you can see, 1.8 is 1/4 stop faster than 2.0 and 1.4 is 1 stop faster
than 2.0. 1.2 doesn't fall directly on either 1/4 stop or 1/3 stop, but
is roughly 1/2 stop faster than 1.4.
Moose
Andrew Dacey wrote:
I could be wrong here, but I believe that 1.0 -> 1.2 -> 1.4 -> 1.8 -> 2.0
are all half-stop increments. So the 1.4 is 1/2 stop faster than the 1.8
and the 1.2 is a further 1/2 stop faster still.
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|