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Thread: Leaf Shutter Speedometer Project

  1. #1

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    Leaf Shutter Speedometer Project

    Yesterday member Drew Bedo sent me a PM asking if the circuitry in my Ghostmaster device might be of use in making a shutter speed checker. I wrote back that I did not think so, but at 4AM I awoke with the following idea.

    This strategy is limited to x-synch leaf shutters. I am sure I could write up a patent application for this in few hours and be successful, but my previous experience with patents is they offer little advantage in a niche market. Once we start discussing it here, the invention is "open source" and cannot be patented.

    The blades in a correctly functioning leaf shutter take only a few milliseconds to open or close(If not it needs a CLA). The electronic flash contact contact points close when the blades have flown fully open and open when they start to close. Therefore, the time of contact closure is very close to the exposure time. There should be some very useful information about the actual shutter speed Vs. that indicated if we connect an appropriate circuit to the electronic flash contacts. I know that this could be easily measured with an oscilloscope.

    The scope will also show that the contacts bounce open again for a few micro seconds after closing when the shutter opens. Any circuit for measuring contact dwell time must be able to deal with this. Accurate measurements at very high speeds 1/250-1/500 may not be possible.
    However, at the speeds at which most LF photographers work, less than 1/125, this approach could be very useful.

    One advantage is that the measurement could be easily made with the lens in place on the camera, just before or even during actual film exposure. Perhaps the device could be incorporated in a cable release which also had an X-Synch connection.

    Drew mentioned a possible smart phone interface. This could be wireless I suppose.

    Any interest?

  2. #2
    (Shrek)
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    Re: Leaf Shutter Speedometer Project

    The electronic flash contact contact points close when the blades have flown fully open and open when they start to close. Therefore, the time of contact closure is very close to the exposure time.
    I'm not convinced this is 100% true, especially with shutters that have M/X syncs. Also, using a cheap piece of photo-voltaic material, it is possible to make a 1-piece shutter speed tester that plugs into the jack of a smartphone (using the microphone contact), that can also be used on roller-blind shutters including early Leicas. It's just the photo-voltaic material with a lead and the correct jack soldered on. I'm not sure what the advantage is, as the x-sync tester would at a minimum require a power source (battery) whereas the photo-cell version does not (the photo-voltaic element generates enough voltage to register as microphone output).

  3. #3
    Tin Can's Avatar
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    Re: Leaf Shutter Speedometer Project

    Sounds doable and useful.

    Since I just ruined 8 sheets because my DIY Packard sync failed at f32, I would also like a way of correlating full open shutter to sync which I guess is just the other side of your coin?

    Dual trace Ocilloscope App?

  4. #4

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    Re: Leaf Shutter Speedometer Project

    Neal, isn't your widget just testing the duration of the flash sync signal? Or have I misunderstood your post? I think you'd really want to know the duration of the actual opening (and to some extent the profile of the light curve), and for that I suspect you're better off with a light sensor rather than looking at the trigger signals - which after all may not, on a lens in need of servicing, occur quite when you expect them.

    Neil

  5. #5
    Tin Can's Avatar
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  6. #6
    Drew Bedo's Avatar
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    Re: Leaf Shutter Speedometer Project

    Neal: Thanks for kicking this off with a serious discussion and a sophisticated approach.. I brought this subject up maybe two years ago and got some dismissive responces on another website.

    I have no engineering or electronic project experience, so I deffer to about anyone else on theory or technical practicalities. But I would like to expand on my idea:

    My concept is much like Barnicle's—a light sensor (photo-voltaic or CdS) senses the light and generates a signal. This is turned into a tone whih is analysed by an audio program. The curve of light intensity over time is the data set, but the curve doesn't need to be displayed only a usable shutter speed. The application on the phone can be tweeked to display a useful shutter speed from this curve.

    I envision a "widget" that mounts to the front of the lens like a clip-on or slip-over lens cap. The signal could be sent to the smart phone or tablet via cable or Bluetooth. This will allow determining variability in shutter speeds when in deep cold or high heat/humidity as conditions change. A measurement could be made in the field prior to taking a shot and that info could be used in making exposure decisions.

    It is my hope that someone will publish a circuit diagram and parts list for the widget, and perhaps someone else will develop the app or apps that do the processing. This could be used with any film camera I think. There may be some processing trick for focal plane shutters.
    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!

  7. #7

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    Re: Leaf Shutter Speedometer Project

    Randy, I'm getting "invalid URL" from the link you sent.
    My flickr stream

  8. #8
    Tim Meisburger's Avatar
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    Re: Leaf Shutter Speedometer Project

    Neal, I prefer your idea. Setting up the photovoltaic tester takes time, and is not really something you could do int he field. On the other hand, the iphone tester that works off sound is easy to use in the field, and maybe accurate enough for our needs?

    Randy, what kind of sync are you using on your Packard? All I have is a piece of bare stranded copper wire that the piston hits at full extension. It took about ten minutes to make with hot glue, and looks it, but it fires reliably.

  9. #9

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    Re: Leaf Shutter Speedometer Project

    Quote Originally Posted by rbultman View Post
    Randy, I'm getting "invalid URL" from the link you sent.
    The 'correct' link appears to be this.

    A shutter timer can be a very, very simple thing. Here is a simple option, and another, that plugs in to the microphone port on a computer and can be 'displayed' using, for example, a simple audio-editor such as Audacity. The signal from the device is a voltage under 1Volt, just like that from a microphone, so the audio-editor is effectively a pseudo-oscilloscope in this case.

    Edit: Don't bother messing around with a laser pointer as mentioned in the links. Just use a decent LED torch or bike-light -- the wider light source is MUCH quicker and easier to set up.

  10. #10

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    Re: Leaf Shutter Speedometer Project

    I'm pleased that there has been such interest and that some members seem to have a good grasp of what I am proposing. The next step is to test a shutter with an o-scope and determine how closely X contact dwell time relates to shutter speed. Shutters are calibrated to account for exposure produced at opening and closing, but at slower speeds using the low speed gear train this effect is a negligible percentage of total exposure.

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