RE: stops and scales
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 calcrounded stops stops 1 f 1 0 1 f 1 0 1.189166052 f 1.190.5 1.122462047 f 1.120.33 1.4 f 1.4 1 1.259921047 f 1.260.66 1.664832473 f 1.661.5 1.4 f 1.4 1 2 f 2 2 1.571446866 f 1.571.33 2.378332105 f 2.382.5 1.763889466 f 1.761.66 2.8 f 2.8 3 2 f 2 2 3.329664947 f 3.333.5 2.244924094 f 2.242.33 4 f 4 4 2.519842094 f 2.512.66 4.756664209 f 4.764.5 2.8 f 2.8 3 5.6 f 5.6 5 3.142893732 f 3.143.33 6.659329893 f 6.665.5 3.527778932 f 3.523.66 8 f 8 6 4 f 4 4 9.513328419 f 9.516.5 4.489848188 f 4.494.33 11 f 11 7 5.039684188 f 5.044.66 13.08082658 f 13.08 7.5 5.6 f 5.6 5 16 f 16 8 6.285787463 f 6.295.33 19.02665684 f 19.03 8.5 7.07863 f 7.065.66 22 f 22 9 8 f 8 6 26.16165315 f 26.16 9.5 8.979696376 f 8.986.33 32 f 32 10 10.07936838 f 10.08 6.66 38.05331367 f 38.05 10.511 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 o
RE: stops and scales
Scott Fine wrote: > 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 Hi Scott, Nope, sorry -- the results are close, but the method is not correct. Photographic stops are a geometric progression, not an arithmetic one. That means to generate the series, you ~multiply~ by a constant factor. To get the series of whole stops, start with 1, and multiply by 2^0.5 (that is, the square root of two). To get the series of half-stops, start with one, and multiply by 2^0.25 (that is, the fourth root of two, which is also the square root of the original square-root-of-two factor). To get the series of third-stops, start with 1, and multiply by 2^0.1667 (that is, the sixth root of two, which is also the cube root of the original square-root-of-two factor). See the pattern? Bill Peifer Rochester, NY - 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 .
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 .
stops and scales
I am fairly new to photography (3 years) and, while I am better at the math these days, it is still a source of confusion for me. 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... Of course I am familiar with 1.7, 2.5, 3.5, 4.5, 6, 9, 13, 14, 19... because these are either fast Pentax lenses or the numbers show up in the meter when I shoot shutter priority or automatic. (Question coming up, I promise.) My questions concern the measurements between stops. I believe that the difference between 2.8 and 4.0 is a full stop which can also be measured in shutter speed, e.g. 1/250 to 1/500. Assuming that this is correct, I can deduce that a change from 2.8 to 3.5 is a 1/2 stop. Unfortunately, this can only be true if 3.5 is the only stop that can exist between 2.8 and 4.0, and this, of course, must be false. So, finally, the questions are: 1. What is the real scale? 2. Other than setting the auto bracket feature to 1/3, how does one make a 1/3 shift? 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 .
