Rear and slow sync with LF

Discussion in 'Large Format Cameras and Accessories' started by Prime, Nov 7, 2002.

  1. Prime

    Prime Member

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    Just curious - is there a way to set an LF lens so that it will sync with the rear curtain or sync slowly? I know that most people probably wouldn't use these techniques with LF, but I may. Thanks!
     
  2. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Rear curtain sync only applies to shutters with a rear curtain (i.e., focal plane shutters), and last I checked, that wasn't a feature available on the Speed Graphic.

    As for "slow sync," sure leaf shutters sync at any speed with electronic flash (barring a few instances with studio lights at full power, where the flash duration may exceed the highest speed of the shutter), but the flash will still happen at the beginning of the exposure.

    It might be an interesting project to attempt to modify a leaf shutter so that it syncs at the end of the exposure.
     
  3. bmac

    bmac Member

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    David,

    How would having the flash at full power affect the sync? I was under the asumption that the only time you had to worry was when you had the flash units powered way down, not powered all the way up...
     
  4. Prime

    Prime Member

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    David,

    With "rear sync" I was actually referring to the shutter syncing at the end of the exposure.

    Do you think some kind of sophisticated flash could be set to sync at the end of the exposure?

    Thanks.
     
  5. William Levitt

    William Levitt Member

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    It sounds like you are trying to achieve "ghost trails" BEHIND the object instead of in front of the object (which would occure if the flash popped at the begining of a time elapsed shot).

    If the exposure is long enough, ie. a few seconds or more, then just pop the flash by hand.
     
  6. Prime

    Prime Member

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    Good idea. Thanks, William.
     
  7. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    bmacphoto: The case I was referring to was when you have studio flash units at full power, in some cases the flash duration might be as long as, say 1/340 sec. If you use a shutter speed of 1/500 sec., the flash duration will be longer than the time the shutter is open. There is no particularly good reason to use such a high shutter speed in the studio anyway, since the flash is likely to be so much more powerful than the ambient light, that you could use a sync speed of 1/15 sec. or even slower in some cases without noticing a difference.
     
  8. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I think William's suggestion is the most practical solution. It's not that hard, and I use open flash technique with lenses that have no shutter or an unsynched shutter.

    The idea of modifying a shutter for sync at the end of the flash is an interesting one. The X-sync mechanism is just a simple switch. You might try it with some older shutter that is easier to work on, like an Ilex, rather than a modern shutter which is much more complex. Normally, on X-sync, the flash fires when the shutter is all the way open. You would need to locate the mechanism that closes the shutter and build a sync switch into it so that the flash would be fired just before the shutter closed. I think there is an Ed Romney book on repairing older shutters. Maybe study that, and see what you can rig up.
     
  9. DKT

    DKT Member

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    FWIW--we did a shot in our studio several years ago, where we needed to have the subject blur/movement like you'd get with a rear curatin sync. On our 4x5, we lit the set with both hotlights (gelled) and strobes. We wound up burning in the motion with the hotlights and then firing the strobe manually at the end of the exposure.....the subject in this case was a hand being jerked back from a steaming pot--via dry ice in water--we timed the motion of the hand & arm of our patient model, with a timer from the lab set on metronome....it took a couple of trys to get it right, but worked & was an interesting diversion from the usual types of shots we do....I realize this is sorta not the right answer, but this is the way we dealt with this problem--we didn't have much of a choice otherwise. BTW-- in our studio we shoot with multiple pops 99% of the time and most times we don't even use the shutters.....we even work on location like this when shooting interiors--using strobesto blow out the ambient or cover the lens between pops......

    it seems like I remember seeing a device for studio strobes that would enable them to work like this....it's been awhile, so maybe my memory is just daydreaming here.....

    KT