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  1. #21
    shutterfinger's Avatar
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    Not a typo.

    All the variables is why I take actual exposurers over test sensors.


    Cock a shutter set on any speed. Place a microphone connected to a computer with an audio recording program running, against the shutter case. Trip the shutter. The first major peak will be the trip lever moving and the next will be the blade controller reaching its limit. The time between the trip peak and shutter blade controller reaching its limit is the "opening time".

    Playing back the recording and listening to it through headphones helps to verify the actual peaks from other mechanical movements which will occur close to the desired ones and distinguish between microphone movement against the case and actual shutter operation.

    In my testers I use 1/4 inch foam core to mount the sensor(s) on using a #28 wire guage drill bit (.1405) for the photodiode mount hole then a #52 wire gauge drill (.0635) for the hole for the test light to access the sensor. This helps reduce the side light picked up from the sensors angle of view. One could make a 2 sensor tester with one sensor at the center of the shutter opening, which is standard for speed testing, and the second at the outer edge of the shutter opening which would be a more accurate test than the microphone method.

  2. #22
    Ken Nadvornick's Avatar
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    Quote Originally Posted by shutterfinger View Post
    Not a typo.
    Wow...

    Then that makes the shutter blade transition time almost as short as the shortest xenon tube burst in some electronic flash units.

    For example, at 1/10,000 (3/30,000) of a sec it's just a tiny bit longer than the shortest duration in the Vivitar 285HV's auto mode flash duration range of 1/30,000 to 1/1000 (30/30,000) of a sec.

    This is actually an order of magnitude faster than I have read about previously.

    Ken
    "They are the proof that something was there and no longer is. Like a stain. And the stillness of them is boggling. You can turn away but when you come back they’ll still be there looking at you."

    — Diane Arbus, March 15, 1971, in response to a request for a brief statement about photographs

  3. #23

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    Shutterfinger, can you fill me in on lubrication requirements for the sliding surfaces of the Flash Supermatic; either via the manual pages or just from your own experience if you prefer?

    The ones I question are the setting lever with sliding contact to the case and the mechanism plate, and the edge of the mechanism plate along which the one coil spring slides (don’t know what to call this spring, but it is the one which is attached directly to the setting lever). Finally, what about the blade controller – should it be completely dry?

    Thanks.

  4. #24
    shutterfinger's Avatar
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    The ones I question are the setting lever with sliding contact to the case and the mechanism plate, and the edge of the mechanism plate along which the one coil spring slides (don’t know what to call this spring, but it is the one which is attached directly to the setting lever).
    Use a thin film of Texaco Unitemp RCX169 grease (I use white lithium grease) to the main drive assembly where it engages the stop stud on the setting lever, on the main drive stud, on the latch at the point it contacts the latch spring, and on the latch where it contacts the retarding sector stud.
    I also put a trace on the main setting spring where it contacts the main drive assembly when the shutter is set (cocked).
    what about the blade controller – should it be completely dry?
    Aperture and shutter blades as well as the shutter blade controller should be dry and free of oil or grease as these lubricants act like glue when on these parts.
    Extra fine powdered graphite as well as other powdered dry lubricants work well and improve the shutter's operation.

  5. #25

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    Just an update - I overhauled the shutter again, this time disassembling it more completely and doing a more “proper” CLA than before. As you can see from the attached before-and-after data, I was able to improve the timing. This comes partly just from adding lube where it is helpful, while keeping it away from where it doesn’t belong! (thanks for the info shutterfinger) But I also reworked some components, including some deburring and sanding, and also shortening the main spring, all to help get the speeds up. I have to admit that I applied grease in a couple of additional places just to make things smoother, for example on the underside of the aperture pointer ring (and yes, you do need to be extremely careful not to let any of that grease migrate to the blades themselves or any part of the blade assembly!)

    Click image for larger version. 

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    I feel I have a much better appreciation and understanding of the workings of this shutter now, including where things can go wrong over time that may account for them tending to run slow. Oh, and I also have a more detailed version of this data which explores how repeatable the shutter speeds are (sometimes not very!), and the effect of aperture on the effective timing, if anyone is interested.

  6. #26

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    I thought I might chime in on this interesting tangent discussion about shutter speed testing too.

    First of all, the geometric effect that some are talking about that results from the finite opening/closing time of the blades, has been well described previously in terms of “shutter efficiency.” I am fortunate to have a copy of Photography Its Materials and Processes by Neblette, which has a very good discussion of such things, and quotes ASA Standard PH.3.4-1952:

    The efficiency of between-the-lens shutters at a particular diaphragm opening and a particular exposure time setting is the ratio of the quantity of light actually transmitted by the shutter at those settings to the quantity of light that would have been transmitted had the shutter been fully open at that diaphragm opening for that total open time.”

    So the descriptions above have hit upon a real, and important subtlety that should be thought about when measuring and interpreting shutter speed test results. The efficiency can account for up to at least a full stop difference in measured "speed" at the high end, depending on how you measure/interpret the data. It is also a function of the aperture setting. When using the photodiode-timing approach for testing shutter speeds, that is just one of a number of subtleties that need to be considered. Other factors I thought of when I was first looking into this approach include the geometry of the optical layout in terms of collimated vs. flood illumination and/or need for aperturing. An example of this is that you might need a different configuration for a focal plane shutter compared to a leaf shutter. Another thing to consider is that ideally the photo-detector should not have so much light on it as to be saturated, since it will tend to rail at that maximum value too quickly and yield inaccurately long exposure times. Also, do you know what the response time of your circuit is, and whether it is fast enough for your highest speeds? Having said those last two, maybe published circuits already have this all worked out? Anyway, don't get me wrong; I am not saying that this isn't a good method - certainly it can work just fine - but I wanted to point out that there are some subtleties to take into account that are sometimes overlooked.

    Over on photonet I talked about at least four different ways I could think of to measure shutter speeds. But when it came time to finally putting a system together I could use, I decided I really liked the digital camera approach as described here or here the best. It is hard to find a really good description of this method, but in a nutshell it involves using a digital camera (which must have a manual mode and be capable of generating histograms), and comparing light through the shutter/camera under test when that shutter is used, versus when the shutter on the digital camera is used. The nice thing with this approach is that it measures light throughput in a photographically meaningful way without having to worry about interpreting timing intervals, shutter efficiency, etc. In fact it automatically gives you what you might call the effective shutter speed, regardless of efficiency concerns or anomalies of the opening/closing behavior of the shutter. Of course this method has its subtleties too! And, I can offer tips if anyone using it. But I wanted to at least point it out for anyone who might not have heard of it before.

  7. #27
    Hatchetman's Avatar
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    Using a DSLR seems pretty easy. So simple, I'm surprised I never thought of it myself. I'll give it a try tonight.

  8. #28
    shutterfinger's Avatar
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    I built 2 testers, one using a special high switch speed photodiode and one using Radio Shack photodiodes. The high switch photodiodes are rated for a rise and fall time of 100 nano seconds (.00001 milliseconds) each. I get no difference in test results between the two testers whether testing leaf shutters or focal plane shutters.
    One of the shutters I tested with both is a Graflex 1000 whose 1000 speed tested 750, a half stop slow.

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