I DID THIS IN EXCEL A WHILE BACK. I THINK ITS CORRECT: 1/2 stops 1/2 stops 1/3 stop calc 1/3 stops rounded calc rounded stops stops
1 f 1 0 1 f 1 0 1.189166052 f 1.19 0.5 1.122462047 f 1.12 0.33 1.4 f 1.4 1 1.259921047 f 1.26 0.66 1.664832473 f 1.66 1.5 1.4 f 1.4 1 2 f 2 2 1.571446866 f 1.57 1.33 2.378332105 f 2.38 2.5 1.763889466 f 1.76 1.66 2.8 f 2.8 3 2 f 2 2 3.329664947 f 3.33 3.5 2.244924094 f 2.24 2.33 4 f 4 4 2.519842094 f 2.51 2.66 4.756664209 f 4.76 4.5 2.8 f 2.8 3 5.6 f 5.6 5 3.142893732 f 3.14 3.33 6.659329893 f 6.66 5.5 3.527778932 f 3.52 3.66 8 f 8 6 4 f 4 4 9.513328419 f 9.51 6.5 4.489848188 f 4.49 4.33 11 f 11 7 5.039684188 f 5.04 4.66 13.08082658 f 13.08 7.5 5.6 f 5.6 5 16 f 16 8 6.285787463 f 6.29 5.33 19.02665684 f 19.03 8.5 7.055557863 f 7.06 5.66 22 f 22 9 8 f 8 6 26.16165315 f 26.16 9.5 8.979696376 f 8.98 6.33 32 f 32 10 10.07936838 f 10.08 6.66 38.05331367 f 38.05 10.5 11 f 11 7 45 f 45 11 12.34708252 f 12.34 7.33 13.85913152 f 13.85 7.66 16 f 16 8 17.95939275 f 17.96 8.33 20.15873675 f 20.16 8.66 22 f 22 9 24.69416503 f 24.69 9.33 27.71826303 f 27.71 9.66 32 f 32 10 35.9187855 f 35.92 10.33 40.3174735 f 40.32 10.66 45 f 45 11 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED]]On Behalf Of Scott J. Fine > Sent: Wednesday, August 14, 2002 3:04 PM > To: [EMAIL PROTECTED] > Subject: Re: stops and scales > > > You write: > >Scott J. Fine" <[EMAIL PROTECTED]> wrote: > > > >"I am under the impression that f-stops are measured in a scale that is > >either based on 1 or 1.4, as in: > > > >1, 1.4, 2, 2.8, 4.0, 5.6, 8, 11, 16, 22, 32..." > > > >It's actually based on the square root of 2 (1.414) and has to > do with how > >the area of the aperture is calculated. The f stop is the ratio of the > >aperture diameter to the focal length. An f stop of 1.0 > (theoretical) with a > >50mm lens at infinity would mean an aperture diameter of 50mm. > If you wanted > >to halve the area of the aperture (to reduce the amount of light reaching > >the film by half), you wouldn't halve the diameter because the area of a > >circle is: > > pi x r**2. Halving the radius would result in an aperture one > fourth the > >area (or 2 stops). Therefore, to halve the aperture area you divide the > >diameter (and therefore the radius) by the square root of 2. The > new f stop > >becomes f/1.414 (f/1.4) as the diameter is 1/1.414 of the focal length. > >Divide by the square root of 2 again and you get an f stop of f/2 as the > >diameter is now 1/2 the focal length. Keep dividing by the > square root of 2 > >and you get the rest of the scale. > > Please tell me if this is correct - I subtracted one stop from the next > largest, divided that number by 2 and added the result to the larger > aperture. I cam up with the following 1/2 stop scale. > > 1.414 (1.4) > 1.706 (1.7) > 1.999 (2) > 2.413 (2.5) > 2.827 (2.8) > 3.412 (3.5) > 3.997 (4) > 4.824 (4.5) > 5.652 (5.6) > 6.822 (6.7) > 7.992 (8) > 9.646 (9.5) > 11.301 (11) > 13.640 (13.5) > 15.980 (16) > 19.288 (19) > 22.596 (22) > 30.273 (?) > 31.951 (32) > > And if I take the difference between apertures, multiply by .333 and add > that result to the larger aperture, I get 1/3 stops? As in f/9 being 1/3 > of a stop smaller than f/8? ((11.301 - 7.992)(.333)) + 7.992 = > 9.093 [f/9] > > And thank you all for your answers, even the ones with links to > information > that I have no hope of understanding :) > > s/ > > http://www.eyecafe.net > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .