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Thread: Is the nominal shutter speed listed on the Calument tester correct?

  1. #11

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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Pfsor View Post
    It surely is that accurate, especially for the relatively long times between 1s - 1/30s if it is able to measure a burst of light of 1/250s. Today's common electronics is capable of even greater accuracy than that.
    I too wondered how how much of the variation in times was from the shutter tester and how much from the shutters. When I tested my Mamiya 7 lenses, which have electronically controlled leaf shutters, I had my answer. I remember being stunned that the 1/2 came out to .50000 and the 1 was 1.00000 and the others were either dead on or off by a minuscule amount. At that point I determined for practical purposes all the error and variation was due to the shutters, or testing error.

  2. #12
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Larry Gebhardt View Post
    I remember being stunned that the 1/2 came out to .50000 and the 1 was 1.00000...
    Due to the short time intervals being measured, shutter testers use a crystal oscillator as their time reference.
    Crystal oscillators can easily hold accuracies of 10 parts-per-million (0.001%) or better.

    Electronic camera shutters also use crystal timebases, for the same reason.
    As long as the crystal is undamaged, they remain accurate for many decades.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  3. #13

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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Peter Gomena View Post
    Anything less than about 1/6-stop difference is insignificant anyway, right?
    I learned from Ken Rockwell to tape a small piece of paper to my lens boards with my tested shutter speeds so I can see at a glance what they are. Anything less than 1/2 stop off, I don't worry about writing on the paper.

  4. #14

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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Leigh View Post
    Due to the short time intervals being measured, shutter testers use a crystal oscillator as their time reference.
    Crystal oscillators can easily hold accuracies of 10 parts-per-million (0.001%) or better.

    Electronic camera shutters also use crystal timebases, for the same reason.
    As long as the crystal is undamaged, they remain accurate for many decades.

    - Leigh
    Leigh, I'm quite sure we can forget crystals for this application. There is an electronic timer circuit, probably the famous 555 that is used as an oscillator.
    Last edited by Pfsor; 16-Sep-2017 at 12:28.

  5. #15

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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Larry Gebhardt View Post
    I had my answer. I remember being stunned that the 1/2 came out to .50000 and the 1 was 1.00000 and the others were either dead on or off by a minuscule amount.
    That minuscule difference could be given by the exact position of the measuring sensor with regard to the shutter centre. Because of their geometry shutters allow a slightly longer exposures passing through the centre of their opening and shorter ones passing through the shutter curtain edges. Some time difference is then measured accordingly. The shutter tester is that precise.

  6. #16

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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Alan Gales View Post
    Anything less than 1/2 stop off, I don't worry about writing on the paper.
    Really? Have you ever wondered why shutters are marked in 1/3 of stops?

  7. #17
    Jac@stafford.net's Avatar
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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Pfsor View Post
    That minuscule difference could be given by the exact position of the measuring sensor with regard to the shutter centre. Because of their geometry shutters allow a slightly longer exposures passing through the centre of their opening and shorter ones passing through the shutter curtain edges. Some time difference is then measured accordingly. The shutter tester is that precise.
    Agreed. That is a character of sensor's measuring design, but not likely enough to make a difference. Concerning the whole film, the initial small aperture when opening has light still distributing over the whole film, or as much as possible given the lens' coverage.

  8. #18

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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Jac@stafford.net View Post
    Agreed. That is a character of sensor's measuring design, but not likely enough to make a difference. Concerning the whole film, the initial small aperture when opening has light still distributing over the whole film, or as much as possible given the lens' coverage.
    For a moment I didn't understand what you agreed to but then I got it - you probably meant "but not likely enough to make a difference in film exposure"?
    Of course, we're not talking about measuring shutter speeds with their lenses on. But for the shutter opening the difference is surprisingly great. Unfortunately, I don't remember if it is Stroebel or Ray that mention it but if I remember well the difference for the shutter (leaf shutter) center and the edge was about almost 1/3 stop (?). If you have the source you can find it, I don't have access to my books now. Cheers!

  9. #19
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Pfsor View Post
    Leigh, I'm quite sure we can forget crystals for this application.
    There is an electronic timer circuit, probably the famous 555 that is used as an oscillator.
    The accuracy of the 555 timer is several orders of magnitude worse than a crystal.

    I would never use a 555 in the design of a shutter speed tester or any similar device.
    I have used thousands of 555s in designs where absolute accuracy was not needed.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  10. #20
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Is the nominal shutter speed listed on the Calument tester correct?

    Quote Originally Posted by Pfsor View Post
    Really? Have you ever wondered why shutters are marked in 1/3 of stops?
    The deltas (time between adjacent speed settings) can be much more accurate than the absolute speed.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

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