Michael Geschlecht Posted October 2, 2017 Share #81 Posted October 2, 2017 Advertisement (gone after registration) Hello, Michael, Since f/0.7 is 1 stop faster than f/1.0 would you explain your reasoning please? Pete. Hello Pete, It all has to do with rounding off. In the World in general people often use round numbers. For example: When discussing "pi" very few people use a number like: 3.14159265358979323846 and then keep adding to it. In photography things are pretty much the same. F stops, like shutter speeds, are sometimes rounded off numbers. Given that 0.96 is the rounded off number for 1/8th of a stop larger than 1.0 And that 0.94 is the rounded off number for 1/6th of a stop larger than 1.0 What else would 0.95 be other than 1/7th of a stop larger than 1.0? It fits there nicely. Right in between. Best Regards, Michael Link to post Share on other sites More sharing options...
Advertisement Posted October 2, 2017 Posted October 2, 2017 Hi Michael Geschlecht, Take a look here Leica 75mm Noctilux to be realised in 2017.... I'm sure you'll find what you were looking for!
luigi bertolotti Posted October 2, 2017 Share #82 Posted October 2, 2017 ...For example: When discussing "pi" very few people use a number like: 3.14159265358979323846 and then keep adding to it. Michael, you surely know that in Indiana they tried to pass a State Bill which affirmed that PI=3.2 (it was 1897 - the Bill was NOT approved) ... and that an American wrote a very good paraphrasis of Poe' "The Raven" made of 740 words , each of the length of Pi digits (the title is part of the Poem : "Poe E. : near a raven : Midnights so dreary, tired and weary..." Link to post Share on other sites More sharing options...
pico Posted October 2, 2017 Share #83 Posted October 2, 2017 Rather than ƒ stops would it be feasible to use T stops? Link to post Share on other sites More sharing options...
darylgo Posted October 2, 2017 Share #84 Posted October 2, 2017 My math results in a fifth of a stop, but it could be faulty as I was educated in the 1960's with the new math. The square of the f-stop is put on a linear scale to determine differences, so .95 x .95 = .90 , .7 x .7 is .49, and of course 1 x1 = 1, so 1/5 stop from f1, and 4/5 stops greater than f 0.7 . Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 2, 2017 Share #85 Posted October 2, 2017 Michael, you surely know that in Indiana they tried to pass a State Bill which affirmed that PI=3 (it was 1897 - the Bill was NOT approved) ... and that an American wrote a very good paraphrasis of Poe' "The Raven" made of 740 words , each of the length of Pi digits (the title is part of the Poem : "Poe E. : near a raven : Midnights so dreary, tired and weary..." Hello Luigi, I did not know either of those 2 things. By the way, I think that "pi" is a little longer than 740 decimal places. Best Regards, Michael Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 2, 2017 Share #86 Posted October 2, 2017 Hello Luigi, ... By the way, I think that "pi" is a little longer than 740 decimal places. Best Regards, Michael Of course... they are infinite... but is anyway a significant achievement Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 2, 2017 Share #87 Posted October 2, 2017 Advertisement (gone after registration) Rather than ƒ stops would it be feasible to use T stops? Hello Pico, I think T stops (actual light transmission) as opposed to F stops (Mathematical relationship between the distance from the second nodal point of a lens to the film plane in relation to the diameter of that lens's opening where the aperture blades are.) is more something which is useful in the movie industry where different segments of film exposed here & there, often in different cameras, need to maintain pretty much the same negative density when they are spliced together. In most still photography small differences in negative density from frame to frame are often not that significant. Best Regards, Michael Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 2, 2017 Share #88 Posted October 2, 2017 Hello Everybody, If 1.0 is the whole stop. And 0.71 (approximately) is the next stop LARGER. Because .71 is approximately 1/2 of 1.414213562. And: 1.414213562 (approximately) is the stop in the middle between F1.0 & F2.0 If we divide 1.0 by (approximately) 1.05756639 seven (7) times we get:1.0 - 0.95 - 0.90 - 0.86 - 0.82 - 0.78 - 0.74 - 0.71 All numbers rounded off. Each number being 1/7th of a stop more, or less, than the other. Best Regards, Michael Link to post Share on other sites More sharing options...
pico Posted October 2, 2017 Share #89 Posted October 2, 2017 Each number being 1/7th of a stop more, or less, than the other. 1/7th is 0.14 I hate fractions. Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 2, 2017 Share #90 Posted October 2, 2017 1/7th is 0.14 I hate fractions. Hello Pico, That is why it is rounded off to a nice, neat 0.95 Imagine if it was 1/17th of a stop. That would be an ungainly 0.98 (rounded off). Best Regards, Michael Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 3, 2017 Share #91 Posted October 3, 2017 I love these discussions on fractions of stops... I played for 1/2 hour with Excel using the effective formula to compute fractions of f stops... and of course it results that it's all about the ROUNDING... not only of the computed value, but also from the f value you start with... I mean : - Starting from 0,7 , 1/7th stop increments : 0,7.... 0,91 - 0,94 - 1 - Starting from 0,5 (next "round" aperture), 1/7th stop increments : 0,7... 0,91 - 0,95 - 1 Why ? Because 0,7 is indeed an aproximation of 0,7071.... (half of Square root of 2) and if you put 0,707 in the formula with 1/7th increments (but rounding Always the result to 2 decimals) you get 0,7... 0,91 - 0,95 - 1 SO : my conclusion is that "f0,95 is 1/7th stop faster than f1" is the BEST SIMPLE ASSESSMENT. to further check... if we use 1/6th increments we get 0,93 or 0,94 (starting from 0,7 or 0,707) So 1/6th is surely a rougher evaluation and if we use 1/8th increments we get 0,95 or 0,96 (starting from 0,7 or 0,707) So 1/8th is too a no bad evaluation ... but if you make the computation starting from 0,5, again you get 0,96... q.e.d. "1/7th is the best" Link to post Share on other sites More sharing options...
michaelwj Posted October 3, 2017 Share #92 Posted October 3, 2017 Maybe the solution is to use 3 significant figures in f-stop scales? In the end it's all pointless as the reported aperture is an approximation to begin with. As for t-stops, the vignetting wide open would leave many disappointed with their new Noctilux t/1.32 Link to post Share on other sites More sharing options...
pop Posted October 3, 2017 Share #93 Posted October 3, 2017 The number of f-stops is the logarithm to the base 1.41... (the square root of 2). The number given above (i.e. about 1/7 of an f-stop for 1:095) happens to be correct, but not for the reasons given later. The function is used as LOG(number, base) in LibreOffice. There must be an equivalent function in Excel, possibly by the same name. It's important that the base can be explicitly given, and it must be the square root of two ( SQRT(2) in LibreOffice). The solution we're looking for is therefore LOG(0.95, SQRT(2)) - Excel uses a semicolon instead of a comma in the expression, if I recall correctly. To express that as a fraction, use 1/LOG(0.95, SQRT(2)) and round at will. Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 3, 2017 Share #94 Posted October 3, 2017 The solution we're looking for is therefore LOG(0.95, SQRT(2)) - Excel uses a semicolon instead of a comma in the expression, if I recall correctly. To express that as a fraction, use 1/LOG(0.95, SQRT(2)) and round at will. Identical expression in Excel (apart that my Italian version uses "RADQ" instead of "SQRT"...) Link to post Share on other sites More sharing options...
pgk Posted October 3, 2017 Share #95 Posted October 3, 2017 By the way, I think that "pi" is a little longer than 740 decimal places. I seem to remember something on the television many years ago about Pi having been calculated (and the result published) to one million decimal places. Why I have absolutely no idea ..... Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 3, 2017 Share #96 Posted October 3, 2017 Hello Everybody, Part of the differences come about because many of the numbers used in photography for either shutter speeds or apertures are CONVENIENTLY rounded off numbers. 1/2 of a shutter speed of 1/125 is not 1/60 Just the same as: 1/2 of the F stop of F2 is not F1.4 So whether the number id 0.94 or 0.95 or 0.96 depends on the starting point. I began with F2 being approximately 2.000000000 and went on from there. Best Regards, Michael Link to post Share on other sites More sharing options...
luigi bertolotti Posted October 3, 2017 Share #97 Posted October 3, 2017 I seem to remember something on the television many years ago about Pi having been calculated (and the result published) to one million decimal places. Why I have absolutely no idea ..... They are at billions of digits now... a classical test to evaluate efficency on fast converging algorhitms (a specific branch of math) ... and also of course to flex the muscles of CPUs Anyway (I am a passionate of numbers) I seem to remember that around the 800th decimals there is a string of SEVEN "9" ... so you can forget the rest, truncate, and anjoy a RATIONAL pi Link to post Share on other sites More sharing options...
Michael Geschlecht Posted October 3, 2017 Share #98 Posted October 3, 2017 Hello Luigi, Apple, peach or plum?Best Regards, Michael Link to post Share on other sites More sharing options...
farnz Posted October 3, 2017 Share #99 Posted October 3, 2017 Hello Luigi, Apple, peach or plum? Best Regards, Michael Blackbird for me please. Pete. Link to post Share on other sites More sharing options...
Exodies Posted October 3, 2017 Share #100 Posted October 3, 2017 (I think I’ve done this one before but never mind) What’s the volume of a pizza of radius z and depth a? Link to post Share on other sites More sharing options...
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