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Renato Tonelli
24-Mar-2009, 13:19
I just tested a lens (Nikkor-W 300mm f/5.6) with a Calumet Shutter Tester; What is the math I need to do in order to figure out by how accurate each shutter speed is?

These are some to the numbers I've gotten.

Shutter Speed Test No.
1/60 .2347
1/30 .4031
1/15 .7209
1/8 .13349

Thank you for setting me on the righteous path.

Eric Woodbury
24-Mar-2009, 14:07
do the fraction or get google to do it. 1/60 = 0.0167, 1/30 = 0.033, 1/15 = 0.067, 1/8 = 0.125, 1/4 = 0.250, 1/2 = 0.500, 1 = 1.000

so your 1/8 looks ok. 1/15 I think you have the decimal in the wrong place and it is okay at 0.072, 1/30, same problem and getting a little long. Same with 1/60. All fine if they are consistent. Put the numbers on a sticker on your lensboard.

Ole Tjugen
24-Mar-2009, 14:12
1/60 = 0.01667 sec
1/30 = 0.03333 sec
1/15 = 0.06667 sec
1/8 = 0.125 sec

I really hope you have missed out a zero on those shorter times!

GPS
24-Mar-2009, 14:20
Indeed, it is easy to miss a zero or two on the Calumet tester. A color tape put on the right place helps to see it.

Renato Tonelli
24-Mar-2009, 14:55
Thank You All!

Roger Thoms
24-Mar-2009, 15:23
If you want to see how your reading compare to what the should be you can multiply the denominator by the reading you got. For example 1/8 = .13349. So multiply .13349 x 8 which = 1.0679. Then round that figure of to a whole number which = 1 then put it over 8 which is 1/8. Very close.

With the 1/60 = 0.2347, take .2347 x 60 = 14.082 round off to 14 then put over 60 which is 14/60 sec. which is way off, better test again, make sure the decimal is in the right place and if still way off have the shutter serviced. This is an old carpenters trick. Useful since our stupid tapes have 1/4, 1/8, 1/16 etc. on them.

Roger Thoms

Ernest Purdum
24-Mar-2009, 16:26
Don't worry too much about accuracy. Consistency is much more important.

Renato Tonelli
25-Mar-2009, 06:51
Update: Re-tested and the shorter times are definitely off; time for a CLA.