Archived posting to the Leica Users Group, 2000/03/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]One more log for the fire. Here's a table with all the answers. It lists in order the powers of two, f/stop rounded up, and inter-f/stop increment. Pwr of 2 Fstop Increment 0.00 1.0 0.17 1.1 1/3 0.25 1.2 1/2 0.33 1.3 2/3 0.50 1.4 0.67 1.6 1/3 0.75 1.7 1/2 0.83 1.8 2/3 1.00 2.0 1.17 2.2 1/3 1.25 2.4 1/2 1.33 2.5 2/3 1.50 2.8 1.67 3.2 1/3 1.75 3.4 1/2 1.83 3.6 2/3 2.00 4.0 2.17 4.5 1/3 2.25 4.8 1/2 2.33 5.0 2/3 2.50 5.7 2.67 6.3 1/3 2.75 6.7 1/2 2.83 7.1 2/3 3.00 8.0 3.17 9.0 1/3 3.25 9.5 1/2 3.33 10.1 2/3 3.50 11.3 3.67 12.7 1/3 3.75 13.5 1/2 3.83 14.3 2/3 4.00 16.0 4.17 18.0 1/3 4.25 19.0 1/2 4.33 20.2 2/3 4.50 22.6 4.67 25.4 1/3 4.75 26.9 1/2 4.83 28.5 2/3 5.00 32.0 5.17 35.9 1/3 5.25 38.1 1/2 5.33 40.3 2/3 5.50 45.3 5.67 50.8 1/3 5.75 53.8 1/2 5.83 57.0 2/3 6.00 64.0 6.17 71.8 1/3 6.25 76.1 1/2 6.33 80.6 2/3 6.50 90.5 6.67 101.6 1/3 6.75 107.6 1/2 6.83 114.0 2/3 7.00 128.0 Skip At 3/7/00 10:12 AM +0000, you wrote: >Some maths!!! > >f stops are calculated using the surface area of the lens. >which is related to the diameter (pi r square as you might remember) > >This you can recognize looking at the f stops at the lens: > >1 -- 1.4 -- 2 -- 2.8 -- 4 -- etc. > >which equals > >2^0 -- 2^0.5 -- 2^1 -- 2^1.5 -- 2^2 -- etc. (2^0 means 2 raised to the power >of 0) > >so ... > >2^0.5 which also can be noted as square root 2 actualy is 1.1415... >Al the figures engraved on your lens are truncated. You can see this when >looking at the more smaller apertures. It starts with each second figure >multiplied by two but at the end it changes: f1.4 f2.8 f5.6 f11! f22 f45! >f11 is 2^3.5= 11,3. >Look at this: f5.6 is 2^2.5. However 2^2.5 equals 5,65685 which is rounded >off as 5.7 >So f5.6 is actually closer to f5.7 > >The question is, what f stop is 1.5? >or ... 2 raised to which power equals 1.5? >This is caluclated by 2 log 1.5 (sorry for the math) which equals 0.58496 >We can find this number somewhere between 0.5 and 1 thus between f14. and f2. >... right. > >0.58496 is 0.08496 higher than 0.5 (fstop 1.4) >The next stop is 0.5 further (2^0.5 -- 2^1, one fstop, remember?!) >and 0.08496/0.5 = 0.16992. > >This means f1.5 is 0.16992 stop further than 1.4 >which equals 1/5.88512 or more or less 1/6 > >so ... > >f 1.5 is +/- 1/6 smaller compared to f 1.4 >(possible truncation of 1.5 and inaccuracies of measuring the >actual apperature not taken into account) > > >Yet another answer!!! > > >Richard. - ----------------------------------------------- Skip Williams Westfield, NJ skipwilliams@pobox.com http://www.skipwilliams.com - -----------------------------------------------