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Thread: PC Sync Debounce

  1. #1

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    PC Sync Debounce

    I wanted to use a modern flash with my Kodak 203mm, but in testing, I found there was awful bounce in the PC sync. I get several uneven pops in a short amount of time. Not sure how many could occur if I set the shutter speed quick enough, but for a longer speed it could easily be several.

    I'll probably wire up a little 555 timer when I get a spare minute, but was just wondering what other folks are doing about these aging mechanical switches.
    Last edited by alt.kafka; 1-Aug-2021 at 19:43.

  2. #2

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    Re: PC Sync Debounce

    I suspect even cheap remote flash triggers debounce. I haven't ever investigated though.

    jeff

  3. #3
    Tin Can's Avatar
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    image

  4. #4

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    Re: PC Sync Debounce

    Quote Originally Posted by Jeff Keller View Post
    I suspect even cheap remote flash triggers debounce. I haven't ever investigated though.

    jeff
    No, they don't. They try to deliver as many flashes as they can discharge.

  5. #5
    (Shrek)
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    Re: PC Sync Debounce

    Per Randy's link, all you need is a capacitor and 2 resistors. Total cost should be under $1.00 if you have a surplus store nearby. No need for a 555 timer, power supply or anything. I would be tempted to modify that circuit with the addition of a Schottky diode so the flash doesn't see a slow voltage ramp-down; that circuit isn't designed for momentary contacts like a flash (?).

  6. #6

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    Re: PC Sync Debounce

    Could be as simple as the contact in the shutter is pitted/oxidized/burnt/gunked up or other parts around it are conducting, so cleaning is needed in the sync system, due to imperfect contacts, contamination etc...

    Steve K

  7. #7

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    Re: PC Sync Debounce

    Quote Originally Posted by Jody_S View Post
    Per Randy's link, all you need is a capacitor and 2 resistors. Total cost should be under $1.00 if you have a surplus store nearby. No need for a 555 timer, power supply or anything. I would be tempted to modify that circuit with the addition of a Schottky diode so the flash doesn't see a slow voltage ramp-down; that circuit isn't designed for momentary contacts like a flash (?).
    Yeah, I don't have a storage scope, so I don't know what the noise or the trigger itself looks like. I'd have to play with it to figure out the timing. It might be adequate. It also depends on whether that contact is on long enough to charge the cap. The advantage of the 555 is very specific setting of the duty cycle. Kind of annoying that a modern trigger doesn't just give you the option to define this in software.

  8. #8
    Tin Can's Avatar
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    Re: PC Sync Debounce

    Any shutter that gives me trouble, including two Kodak 203 get mounted to a Packard shutter

    Some Packards have sync, if not a mini microswitch is installed

    I shoot all strobes or flashbulbs at Packard speed, 1/10 to 1/30 as the light stops motion

    or shoot 'bulb' in dim light
    image

  9. #9

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    Re: PC Sync Debounce

    I've had the same problem with my packard. The thing is, the switch is closed as long as the shutter is open. Any stutter or hesitation would cause multiple triggers. If I get a good crisp actuation it works fine, cleaning everything up (electrically and mechanically) has helped a lot. Not sure how this translates to clockwork shutters. My only "vintage" shutter with sync has been working perfectly fine.

    I haven't worked out a solution yet since the packard seems to be working well enough at this point (I don't do long exposure with flash though). I think I found an off-the-shelf solution at one point but I thought it was ridiculously expensive.

    For fast shutter speeds and strobes with low trigger voltages, a simple DIY solution may work (maybe even an RC circuit as mentioned) but if you have strobes with high voltages or need long exposures it can get more complicated.

    Quote Originally Posted by alt.kafka View Post
    It also depends on whether that contact is on long enough to charge the cap.
    Actually, for this application you probably want to modify the circuit in that doc a little bit so that when the switch is closed it immediately discharges the cap, then the cap slowly charges when the switch is opened.

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