Originally Posted by
Doremus Scudder
Here's my table of shutter speeds in milliseconds with corresponding approximate 1/3-stop fractions.
When I get my shutters tested, I convert the time in milliseconds to the closest 1/3-stop shutter speed. I'll then make a sticker to paste on the lensboard with the corrected shutter speed.
So, for example, let's say the 1/15th-second setting on the shutter comes in at 83 milliseconds. On my table, that's closest to 80 milliseconds, which is 1/12 second, which is 1/3 stop slower than the standard 1/15th second. So, I'll mark that as 1/15- (using the "minus" sign). And say that my 1/125th-setting comes in at around 14 milliseconds. That's closest to 12.7 milliseconds on the chart, which is 1/80th second, which is 1/3 stop faster than the standard 1/60th setting (i.e., my 1/125 setting is about 2/3-stop slow). So, I'll mark that 1/60+ (using the "plus" sign) on my sticker. Just remember that the plus and minus signs refer to the numbers: Minus means More exposure and Plus is Less exposure when working with the fractions-of-a-second shutter speeds.
Then, when setting the exposure, I'll just adjust with the aperture. Say my meter wants 1/60th at f/22. I'll set my shutter at 1/125th, which is 1/60+ (1/3 stop less exposure than 1/60th) and then set the aperture to 1/3 stop more open than f/22 to compensate. (if there are no 1/3-stop hash marks on the shutter, I just estimate). This method gets me to within 1/6 stop overall, close enough for color transparency work even.
I work in 1/3-stop increments when metering anyway, since my meters are all marked with third-stop hash marks. I'd notate the above in my exposure record as "f/22- at 1/60+." The good thing about this is that the minus sign for both shutter speeds and aperture means more exposure and the plus sign for both means less exposure.
Hope that all makes sense; it will after looking at the chart and going through the above examples again.
Best,
Doremus
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