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  1. #1

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    Tempor shutter speeds

    After having been confirmed in another thread (Tessar lens) that the lens on my Welta Weltax is good stuff, I turned my attention to the shutter.

    It's my impression that many of these old folders often combined good glass with less excellent shutters or the reverse. Mine has a TEMPOR shutter that is recently cla-ed. Speeds and self timer are running fine, except the fastest shutter speed promising 1/250.

    I took interest in finding how much of the open time the shutter blades spend travelling from closed to fully open and back again from fully open to closed. So I tested the speed at 1/250 and f:16 which gave 1/106, and also at 1/250 and f:3.5 which gave 1/180.

    To measure the open time at max aperture, I only let light through to the periphery of the lens by covering with a cardboard. See photo.

    Ironically a little math shows that the time the shutter blades spend on opening/closing is close to 1/250!
    Attached Thumbnails Attached Thumbnails covering-lens.jpg  
    Last edited by SalveSlog; 03-21-2014 at 11:26 AM. Click to view previous post history.

  2. #2

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    Quote Originally Posted by SalveSlog View Post
    After having been confirmed in another thread (Tessar lens) that the lens on my Welta Weltax is good stuff, I turned my attention to the shutter.

    It's my impression that many of these old folders often combined good glass with less excellent shutters or the reverse. Mine has a TEMPOR shutter that is recently cla-ed. Speeds and self timer are running fine, except the fastest shutter speed promising 1/250.

    I took interest in finding how much of the open time the shutter blades spend travelling from closed to fully open and back again from fully open to closed. So I tested the speed at 1/250 and f:16 which gave 1/106, and also at 1/250 and f:3.5 which gave 1/180.

    To measure the open time at max aperture, I only let light through to the periphery of the lens by covering with a cardboard. See photo.

    Ironically a little math shows that the time the shutter blades spend on opening/closing is close to 1/250!
    So the other speeds work at all other apertures? I honestly wouldn't want to be victim of over exposure if I used 1/250th! Print film probably is forgiving enough but something like Velvia 50 would probably not be!

    Just curious how would one test actual shutter speed? I have a 35mm that I sorta screwed up, the shutter is stuck at an unknown high speed (my guess is between 250 and 1000 :O) I simply shined light into the front of the lens and opened the back and watched how quick the light appeared but thats not scientific....is their a way to properly time it with maybe a DSLR or iPhone app or is their some official device that only a physics professor would have....

  3. #3
    Jim Jones's Avatar
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    As SalveSlog demonstrated, the time required to open and close the blades can be significant at the highest speeds. A shutter speed tester that integrates the light passing through the shutter at the aperture that will be used for photography is the only really accurate way of testing a between-the-lens shutter at its higher speeds. Shutters can indicate a slower speed when they are tested at wide apertures.

  4. #4
    AgX
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    Quote Originally Posted by Jim Jones View Post
    Shutters can indicate a slower speed when they are tested at wide apertures.
    When they are used at small apertures.

  5. #5
    Jim Jones's Avatar
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    Quote Originally Posted by AgX View Post
    When they are used at small apertures.
    Thanks for catching that. I meant shutter testers.

  6. #6

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    I recently tested an Ilex shutter and put up a typical oscilloscope trace in my thread "O_ER.." in the camera building section

    The trace is with the shutter at 1/100 second. and the aperture was set at f/1.9
    It shows the penumbra with the lens stop wide open.
    The trace can be calibrated knowing that the illumination was an incandescent lamp flickering at 120 Hz. Anyway the oscilloscope is accurate and shows that the shutter was fully open for about 11 millisec and took about 2 millisec to open fully at f/1.9 and less than 1 millisec to close.


    I have tested 2 Graphex and a Prontor shutter and the penumbra shown in the trace is typical.



 

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