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Thread: Concept for a Shutter Tester

  1. #21

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    Re: Concept for a Shutter Tester

    Afterthoughts:
    Check that the input sensitivity can be adjusted over at least say 10mV...1V
    On-screen cursors: I take them for granted on a scope, if absent on a cheap one, time measurements would be less convenient.

  2. #22
    Tin Can's Avatar
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    Re: Concept for a Shutter Tester

    Good advice Bernard. Thank you.

    I am now shopping for a higher end oscilloscope. Maybe USB.

    The Tektronix scope I used 20 years ago to check ultrasonic bolt elongation was very expensive. I see prices for ultrasonics have gone way down and include a waveform screen.

    Quote Originally Posted by Bernard_L View Post
    Afterthoughts:
    Check that the input sensitivity can be adjusted over at least say 10mV...1V
    On-screen cursors: I take them for granted on a scope, if absent on a cheap one, time measurements would be less convenient.
    Tin Can

  3. #23

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    Re: Concept for a Shutter Tester

    Quote Originally Posted by Randy Moe View Post
    The Tektronix scope I used 20 years ago to check ultrasonic bolt elongation was very expensive.
    Interesting. I had to deal with screw pre-load in assemblies that were cooled to 4K (liquid Helium). Had to just torque the screws, rely on modeling and a guesstimate of the importance of friction in the pre-load.
    [off-topic]

  4. #24
    Drew Bedo's Avatar
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    Re: Concept for a Shutter Tester

    Umm. . . .What about using a DSLR or High-End Mirrorless camera to take a video of the shutter's open-close cycle? A high-speed video would give the needed input for shutter speeds typical of most LF shutters.
    Drew Bedo
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    There are only three types of mounting flanges; too big, too small and wrong thread!

  5. #25

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    Re: Concept for a Shutter Tester

    Quote Originally Posted by Drew Bedo View Post
    Umm. . . .What about using a DSLR or High-End Mirrorless camera to take a video of the shutter's open-close cycle? A high-speed video would give the needed input for shutter speeds typical of most LF shutters.
    It may be useful for the lower speeds, but for higher speeds it would not be accurate. With the machine vision cameras I use I can take 700 frames per second using Format 7 feature, by taking only a little crop of the sensor, and this would be suitable for 1/50 perhaps with 7% accuracy (50/700x100).

    Your idea would be good for 1s to 1/4 speeds perhaps, may be 1/8.

  6. #26

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    Re: Concept for a Shutter Tester

    Let me add to that:

    Quote Originally Posted by Pere Casals View Post
    It may be useful for the lower speeds, but for higher speeds it would not be accurate. With the machine vision cameras I use I can take 700 frames per second using Format 7 feature, by taking only a little crop of the sensor, and this would be suitable for 1/50 perhaps with 7% accuracy (50/700x100).

    Your idea would be good for 1s to 1/4 speeds perhaps, may be 1/8.

    One thing you can do with a DSLR mouted in the back is exposing a DSLR shot two times, one with the DSLR shutter (with the LF lens shutter open, T position), and the next shot with the DSLR shutter open (in T position) and exposing with the LF lens shutter.

    Then you can compare both digital shots, as the DSLR shutter time is very reliable you may see how much the effective LF shutter speed is close to the the marked speed, if shots are inspected in raw mode then you can compare the average pixel values (linear) of both shots to even calculate the missmatch factor.

    IMHO this would be the right way to use a DSLR as a shutter tester, you would only need a lensboard with a macro extension ring bayonet to attach the dslr in the lensboard, and that lensboard would be attached to the back of a monorail, that will take the lesboard. This is interesting because it would be also useful to make calibrations for aperture scales, obtaing not the exact geometric aperture scale but effective aperture, that's good enough for most photographers.

  7. #27
    Paul Ron's Avatar
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    Re: Concept for a Shutter Tester

    Quote Originally Posted by Pere Casals View Post
    Let me add to that:




    One thing you can do with a DSLR mouted in the back is exposing a DSLR shot two times, one with the DSLR shutter (with the LF lens shutter open, T position), and the next shot with the DSLR shutter open (in T position) and exposing with the LF lens shutter.

    Then you can compare both digital shots, as the DSLR shutter time is very reliable you may see how much the effective LF shutter speed is close to the the marked speed, if shots are inspected in raw mode then you can compare the average pixel values (linear) of both shots to even calculate the missmatch factor.

    IMHO this would be the right way to use a DSLR as a shutter tester, you would only need a lensboard with a macro extension ring bayonet to attach the dslr in the lensboard, and that lensboard would be attached to the back of a monorail, that will take the lesboard. This is interesting because it would be also useful to make calibrations for aperture scales, obtaing not the exact geometric aperture scale but effective aperture, that's good enough for most photographers.
    excelent point!

  8. #28
    Drew Bedo's Avatar
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    Re: Concept for a Shutter Tester

    Quote Originally Posted by Bernard_L View Post
    The link provided by Randy Moe is instructive. Up to that point in the thread, I was just shaking my head in skepticism. The first part of the Lomo article shows the shortcomings of the sound method. How are you to measure a time from this kind of plot? Why were the red lines placed here rather than there?
    Attachment 183725
    The schematic with a light sensor (phototransistor) is better than similar ones seen elsewhere on the internet, because the current path is closed inside the schematic itself, not inside the (unknown) inside of the phone's or computer's soundcard. What is also good is the fairly low value of the resistor 4.7kΩ, ensuring the response is relatively fast.
    Attachment 183726
    In case you must use a microphone or line input that is not powered, you can include the power source as follows:
    Attachment 183727
    One drawback of soundcard inputs is they have a high-pass filtering, in practical terms, they have a series capacitor, which is why even the better Lomo schematic produces this kind of response, instead of the expected "brick" shape; nevertheless good enough for measuring times. I found that high-pass filtering sometimes more pronounced on the mic input than on the line input, presumably to prevent "proximity pop". And a Terratec external USB sound card to have more extended low-frequency response.
    Attachment 183728
    The ideal circuit uses a photodiode operated a zero-bias, an op-amp wired as current-voltage converter (transimpedance), and a hacked soundcard with a short-circuit across the input capacitance. Or a digital scope, if you have one.
    To come back to this approach for a bit:

    I gather that the sensor is a microphone, and what is measured is the mechanical noises nade by the moving parts of the shutter as it opens and closes.

    Can the microphone be replaced by a light detecting sensor? This would generate a signal more directly associated with the duration of the light passing the shutter. It might clean up the curve displayed.
    Drew Bedo
    www.quietlightphoto.com
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

  9. #29

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    Re: Concept for a Shutter Tester

    Quote Originally Posted by Drew Bedo View Post
    To come back to this approach for a bit:

    I gather that the sensor is a microphone, and what is measured is the mechanical noises nade by the moving parts of the shutter as it opens and closes.

    Can the microphone be replaced by a light detecting sensor? This would generate a signal more directly associated with the duration of the light passing the shutter. It might clean up the curve displayed.
    all those sensors are photodiodes sending electrical signals to the computer audio input, no microphone...

  10. #30
    Drew Bedo's Avatar
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    Re: Concept for a Shutter Tester

    Thanks. Somehow I missed that. sounds really good.
    Drew Bedo
    www.quietlightphoto.com
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

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