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Thread: Speed Graphic Shutter Checking?

  1. #21

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    Re: Speed Graphic Shutter Checking?

    Quote Originally Posted by Doremus Scudder View Post
    Almost every 35mm SLR has a focal-plane shutter. Technicians and repairmen check and repair them regularly. I see no reason why the techniques used for testing a smaller focal-plane shutter will not work for a larger one.

    Doremus
    Doremus - if I'm not completely mistaken, I think there's a complete difference between most if not all 35mm camera focal plane shutters and large format - at least based on my single sample MPP press which I assume to be a common design.

    The 35mm SLRs usually have two blades, both of which move from the same edge but with one some time later than the other: the first one opens and then the second follows it, giving either a moving slit of a specific width for faster speeds, or a fully open gate for slower speeds. The thinner the slot, the less time that a particular point on the negative is exposed, even though the blades move at much slower speeds.

    The large format camera I have, and a number of elderly medium format cameras (I no longer have) had a roller shutter which has a number of slots of varying width cut in a single blind. Once again the width of the slot gives the exposure for a single point on the film, but not all points are exposed at the same time. As the blind is wound to a desired speed, I'd assume that the spring tension increases for faster speeds, and that the slots are not therefore necessarily linearly related to exposure time.

    To measure an exposure time for *any* type of shutter, the easiest way - if you can drive an oscilloscope - requires only a fast light sensor and the oscilloscope. An LED will generate a voltage output (at very low current) when exposed to light: green ones give most in daylight. Connect the led to the input of the scope, place it at the point you want to measure (the centre is a good place to start) and point the lens at some light. Sticking the LED through a black card will keep light from the back of the camera.

    Neil

  2. #22

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    Re: Speed Graphic Shutter Checking?

    barnacle, a moving slit is a moving slit is a moving slit.

  3. #23

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    Re: Speed Graphic Shutter Checking?

    Quote Originally Posted by Dan Fromm View Post
    barnacle, a moving slit is a moving slit is a moving slit.
    Yea, with a Graflex, just a slit... The degree of tension can be adjusted, but providing that all pivots, moving and sliding parts have been cleaned and lubed (and you don't hear a screech or intact shutter hangs up while firing, most optical testers will work to adjust the overall tension...

    The other issue that comes up with these is that sometimes the slits or shutter material stretches where some speeds/tensions are nearly right on, but one (or more) slit settings are off, but you can often work around this by making a new chart depending on what averages out... (I got lucky with my 4X5 RB D when the higher speeds dropped down a little so the speeds were now the "modern" speeds (1/800 became 1/500, 1/300 became 1/250, and down through all speeds nicely correct)...

    But a film test is usually good enough for these shutters (esp E-6 chromes)...

    Steve K

  4. #24

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    Re: Speed Graphic Shutter Checking?

    I wonder if something might be wrong with online accuracy reports by homemakers may be just as knuckleheaded as some of my own concoctions, or worse even. For instance, there are guys out there who have worked very hard to come up with a device for sale, and I appreciate that guys are out there trying. The contraptions that use computer sound cards and audio programs are particularly suspect. Having done that myself some time ago with results I now consider dubious, I wonder if there's any other guys out there who have taken into account the linearity and sensitivity curves of the sending and receiving sources, whether laser or using parts from a mouse, or other parts on hand. Visualize the characteristic curve of film, which is a more commonly understood concept. Certainly the optical sensors and transmitters would need to be matched or discovered. More plainly put, where is the toe of the curve? Or shoulder either. Accurate measurement can only be available in the (linear)straight line of said curve. Otherwise, if it were at and below the toe, then I'd hate to think how many guys out there measuring shutters and finding distressing results may have been closer to correct than they knew. Or vice versa. I wonder what the ordinary voltage range of a typical computer sound card is.

  5. #25
    Jim Jones's Avatar
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    Re: Speed Graphic Shutter Checking?

    HT Finley makes a strong point. Blasting the sensor with too much or too little light can cause inaccuracy. When testing shutters with a CDS cell long ago, the slow response time of the cell was a problem. The size of the sensor or source, whichever is close to a focal plane shutter, should be small in relation to the slit in the shutter. When testing the top speeds of a between-the-lens shutter, the aperture setting affects the reading. Many factors have to be considered in precise testing of cameras.

  6. #26
    jp's Avatar
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    Re: Speed Graphic Shutter Checking?

    Quote Originally Posted by Randy Moe View Post
    Jim, I used scopes at work, but no more work, so I have been looking at the new cheap ones.

    And of course a link to the retail devil. The best thing about Amazon is the reviewers. Many are very good at guiding a buyer. If you read a few dozen good and bad reviews.

    https://www.amazon.com/gp/product/B0...rd_i=393269011
    We've got one of the cheap ones about two years ago at work. They work. Battery life isn't awesome but if you keep a charger handy, no problem. The ergonomics isn't as great as the big beasts with knobs. We chose ones of the little ones for it's portability and it's very convenient for bringing aboard boats and taking on service calls.

  7. #27
    Randy Moe's Avatar
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    Re: Speed Graphic Shutter Checking?

    Quote Originally Posted by jp View Post
    We've got one of the cheap ones about two years ago at work. They work. Battery life isn't awesome but if you keep a charger handy, no problem. The ergonomics isn't as great as the big beasts with knobs. We chose ones of the little ones for it's portability and it's very convenient for bringing aboard boats and taking on service calls.
    I used to fly with a big Tektronix scope and Ultrasonic bolt machine. I measured head bolts inside engines. This was well before 9/11 and I always got an intense check over as I had to carry it in cabin. My overlords deemed this necesssary, toys were worth 100K and trade secret at that time. Later I was instructed to teach Ford how it worked.

  8. #28
    Randy Moe's Avatar
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    Re: Speed Graphic Shutter Checking?

    Here's a guy who is one of the premier experts on Graflex and Speed roller curtain shutters. Here he shows how he tests his handmade new shutters.

    It's a Facebook link to a picture, you do not need to belong to FB. Just look.

    https://www.facebook.com/photo.php?f...&theater&ifg=1

  9. #29

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    Re: Speed Graphic Shutter Checking?

    Quote Originally Posted by Dan Fromm View Post
    barnacle, a moving slit is a moving slit is a moving slit.
    Indeed. But the slit is not made in the same way, and I'd argue that an ability to mend one sort does not necessarily extend to the other. Though there is no doubt that a moving hole in a strip of material is a simpler technology than moving metal blades.

    Neil

  10. #30

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    Re: Speed Graphic Shutter Checking?

    As an experiment today, I took five minutes to use an LED and oscilloscope as discussed earlier. With the lens wide open and an LED torch pointing through the lens, the signal was about 200mV, but clearly showed that the 1/250th second was a shade slow at 4.2ms (should have been 4.0).

    So this is a viable option. Note that (also as discussed) if the lens is stopped down not only will the signal get smaller by 50% per stop (though a brighter light will help) but the shutter will get faster. I didn't measure the rise- and fall-time of the signal - it was a very quick test - but it was under a hundred microseconds for each. The LED should have a response time in microseconds or faster.

    Neil

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