The Museum of HP Calculators

HP Forum Archive 20

 Re: HP Solve Newsletter Jan 2011: Article about LOGsMessage #2 Posted by Dieter on 21 Jan 2011, 8:39 a.m.,in response to message #1 by Frido Bohn Very interesting post. Let me add this: Quote: The result is that the first fraction of log10(x) is always higher than the integer part of the respective number. This is true for x > 1,371. Below that point 10 lg(x) is less than x. Quote: ...estimation of log10(600) would result in a fraction somewhat higher than "6", maybe "2.7" or "2.8". I'd like to add another method for estimating common logarithms - a very simple method if you're familiar with the world of photography. Due to the logarithmic property of light (our eyes see the same brightness difference if the light intensity changes by the same factor (!)) the usual aperture scale is a geometric sequence where each value is sqrt(2) times its predecessor. In other words: the common logs of the aperture values change in 0,15-steps. Which means that logs can be determined easily by simple couting: aperture value 1 1,4 2 2,8 4 5,6 8 11 common log 0,00 0,15 0,30 0,45 0,60 0,75 0,90 1,05 In this case lg 600 is easily estimated to be a bit more than 2,75. It gets even more precise if you're familiar with intermediate values, for instance 1/3-steps, leading to nice 0,05 logarithmic steps. So, knowing that the next 1/3 aperture step after f/5,6 is f/6,3 the unknown lg 600 has to be quite exactly in the center between 2,75 and 2,80 - and in fact it is (2,778). Okay, this is a method specially designed for photo nerds. But I'm sure there're some of us around here... :-) Quote: In order to manage log10 one would have to learn by heart the logarithms within one order of magnitude That's what most photographers have learned from the start - maybe without realizing it. They use geometric sequences like apertures, shutter speeds and ISO-settings and at the same time they think in logarithmic exposure stops (EV). Dieter Edited: 21 Jan 2011, 8:57 a.m.

 Re: HP Solve Newsletter Jan 2011: Article about LOGsMessage #3 Posted by Martin Pinckney on 21 Jan 2011, 11:49 a.m.,in response to message #2 by Dieter Quote: I'd like to add another method for estimating common logarithms - a very simple method if you're familiar with the world of photography... Okay, this is a method specially designed for photo nerds. But I'm sure there're some of us around here... That's what most photographers have learned from the start - maybe without realizing it. They use geometric sequences like apertures, shutter speeds and ISO-settings and at the same time they think in logarithmic exposure stops (EV). Dieter, Indeed, I am one of those photo nerds. As I read Frido's post, I was thinking about this same subject, so thank you for spelling it out so well.

 Logs and Photo nerdsMessage #4 Posted by Dave Shaffer (Arizona) on 21 Jan 2011, 5:18 p.m.,in response to message #2 by Dieter Thanks for the tip on relating f-stops to logs. I suppose that photo nerds (love the term!) have as many cameras and/or lenses as they do calculators! The digital age has caused an explosion in my number of cameras, at least. For almost 40 years, I got by with my Pentax ME film camera and 3 lenses (28, 50, and 135 mm). (Reminds me of the durability of my HP 35 from the same era!) In the last 5 years or so, my digital cameras included HP210, HP318, Canon XT, Canon XTi, Kodak 915, Kodak 981, Pentax K100D, Pentax K10D, and Pentax K20D. Since old Pentax lenses work on the new Pentax DSLRs, I have also acquired some 15-20 lenses (on the shopping site which must not be named). I imagine there are a lot of other photo nerds here. Tell us what you have. Related question: what (perhaps high-priced) item do you own whose operating lifetime is measured at a few hundred seconds?

 Re: Logs and Photo nerdsMessage #5 Posted by Chris Randle (UK) on 21 Jan 2011, 8:22 p.m.,in response to message #4 by Dave Shaffer (Arizona) Quote: Related question: what (perhaps high-priced) item do you own whose operating lifetime is measured at a few hundred seconds? Chateau d'Yquem 1959?

 Re: Logs and Photo nerdsMessage #6 Posted by Martin Pinckney on 21 Jan 2011, 8:59 p.m.,in response to message #4 by Dave Shaffer (Arizona) Quote: Related question: what (perhaps high-priced) item do you own whose operating lifetime is measured at a few hundred seconds? The CCD on your digital camera?

 Re: Logs and Photo nerdsMessage #7 Posted by Dave Shaffer (Arizona) on 21 Jan 2011, 9:35 p.m.,in response to message #6 by Martin Pinckney I am thinking of Martin's answer (include the entire camera, though), although I also like Chris's answer - but he must drink his Chateau D'Yqeum fairly rapidly!! (I am looking forward to savoring my Chateau Lafitte-Rothschild 1996, that my wife bought for me back when it was affordable, for my 65th birthday in a few weeks! I think I will spend more than a few hundred seconds at that.) Consider your camera: average exposure is perhaps 1/100 second; multiply by 20000 or 30000 pictures, and the operating life is several hundred seconds (although shutters on high-end DSLRs are typically rated for 100K or more exposures - so you gain a few more hundred seconds). If you are into time exposures, you gain a lot of "lifetime."

 Re: Logs and Photo nerdsMessage #8 Posted by Eric Smith on 21 Jan 2011, 11:56 p.m.,in response to message #6 by Martin Pinckney CCD sensors on almost all DSLRs now potentially have a much longer operating life, given that they now are used for "live preview" mode as well as for video capture. Even on DSLRs that don't have those features, the short operating life you describe is only due to the way the device is conventionally used, and not due to any limitation of the sensor. The MTBF of the sensor is in the hundreds of thousands of hours. Some photographers use cameras for very long timed exposures.

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