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  1. #11
    Steve Smith's Avatar
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    Quote Originally Posted by tim_walls View Post
    Edit: Just for the pedants.
    That's me then.

    Quote Originally Posted by tim_walls View Post
    On 'simple' flashes, in very simplistic terms you can think of the recharging circuit as being a battery connected to a capacitor which charges the cap up to a nice high voltage - e.g. 250 volts. The capacitor is also connected through a switch to the flash gun; close the switch, and the capacitor discharges all its stored energy through the flash gun in an instant.

    The problem with old flashes is the 'switch' is just the hotshoe.
    I was not aware of any flashes which use the sync. contacts to directly switch the high voltage from the inverter to the tube (I'm not even sure if it would work).

    Most flashes have an inverter which charges the main capacitor up to a high voltage. This capacitor is permanently connected to the flash tube but the tube will not conduct until it is triggered.

    A second small capacitor is also charged up to a high voltage via a large value resistor. It is this small capacitor which is discharged via the sync. contacts into a transformer. The output of the transformer produces a high voltage pulse which triggers the flash tube into conduction.

    In simple flash circuits, the whole of the charge in the main capacitor is discharged into the flash tube. Early thyristor flashes used a thyristor to 'short out' the tube when enough light had been delivered. The thyristor bypassed the flash tube and took the remaining charge out of the capacitor.

    An improvement of this circuit was to use two thyristors. One was connected between the flash tube and the main capacitor and was effectively held on continuously. The second was used to temporarily switch off the first thyristor when enough light was received. This stopped the tube from conducting and had the advantage of preserving the remaining charge in the capacitor to improve charge time between flashes.



    Steve.

  2. #12
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    Quote Originally Posted by Steve Smith View Post
    That's me then.



    I was not aware of any flashes which use the sync. contacts to directly switch the high voltage from the inverter to the tube (I'm not even sure if it would work).
    Now we really are into pedantry - yes, typically the actual connection is to the tube's trigger conductor. The tube itself is of course permanently connected to the high-voltage supply, the trigger pulse gives the gas a kick to ionise it so it will then conduct.

    The actual connection made by the flash hotshoe is from the high-voltage supply to a second step-up transformer which connects to the tube's trigger, such that when the flash hotshoe is closed a pulse in the 10,000volt+ range is applied to the trigger.


    The salient point - that in old-style flash circuits the full flash HV supply is present on the hotshoe - seemed to be made without needing a discussion on the ionisation of xenon, but I am frequently guilty of misjudging the fine line between necessary detail and necessary simplification.

    In other words, even I underestimate the depths to which pedants will stoop .
    Another day goes under; a little bourbon will take the strain...

  3. #13
    DBP
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    As long as we are on the subject, does anyone know what Nikon models will talk to a Sunpak 266D?

  4. #14
    Ken N's Avatar
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    Quote Originally Posted by Steve Smith View Post
    The flashes marked 'made in Japan' are high voltage whereas the rest are low.
    sTEVE.

    Partly true. To the best of my knowledge, no 285HV marked other than "Made in Japan" are high voltage, but there are "Made in Japan" units which are not high voltage.

    Only the oldest units are high-voltage. These flashes, along with the 283 have been around forever and there were a few changes made through the years which can't be identified through external means.

    Always check an older flash with a volt-meter, and don't assume all of them are camera-killers.
    http://www.zone-10.com

    When you turn your camera on, does it return the favor?

  5. #15
    Steve Smith's Avatar
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    Quote Originally Posted by tim_walls View Post
    The salient point - that in old-style flash circuits the full flash HV supply is present on the hotshoe - seemed to be made without needing a discussion on the ionisation of xenon, but I am frequently guilty of misjudging the fine line between necessary detail and necessary simplification.

    In other words, even I underestimate the depths to which pedants will stoop .
    Guilty as charged!

    I did want to make a short simple point but found myself describing the whole circuit.

    I suppose the point I should have made was that whilst it is possible/likely that the voltage on the sync contacts is the same level as the main HT supply, it is however usually connected via a resistor of around 500K to 1M used to charge a small capacitor.

    Steve.

  6. #16

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    An old 283 that I have (from 1981) measures 4.5 volts and so should work on a dslr. But the Wein people say that if you were to use one of their devices...in a "just in case" situation, that the flash won't even fire because the voltage isn't high enough. So, I guess if you have an older 283 or 285 that have high voltages, the Wein device will be good insurance. But, if like me, you have a low voltage flash, you're on your own!

  7. #17
    viridari's Avatar
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    The new 285HV has yet to fry my old Canon EOS Rebel G or my old Mamiya C330. That said, it really is a big heavy flash.

  8. #18
    Steve Smith's Avatar
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    One thing worth remembering is that all of these flashes were designed to work with all cameras. It is only recent paranoa with some digital cameras having low sync. voltage specifications which have brought up this worry.

    Pre-digital no one would have thought about sync. voltage and would have just used whatever flash they had with whatever camera they had.


    Steve.

  9. #19
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    Quote Originally Posted by Steve Smith View Post
    One thing worth remembering is that all of these flashes were designed to work with all cameras. It is only recent paranoa with some digital cameras having low sync. voltage specifications which have brought up this worry.

    Pre-digital no one would have thought about sync. voltage and would have just used whatever flash they had with whatever camera they had.
    Indeed - I reckon 2nd hand flash units are one of the great bargains still to be had and the voltage paranoia has to be part of that.

    If you have a halfway decent handheld meter then all the alphabet-TTL-metering and automatic this-that-and-the-other whatnot is completely unnecessary, and even if your camera does have a low-voltage hotshoe a Wein Safesync is all you need to open up the complete range of flash units on the market.

    Personally I use a Nikon SB28, Vivitar 283 and three of those cheapo fixed-output units I mentioned earlier; cheapo wireless triggers from eBay and/or optical trigger widgets bring it all together, and it all works perfectly with any of my cameras from the most modern to the most ancient. (Of course, the reality is I almost never use all those units, but it's nice to have the option.) The one flash unit I practically never use is the fully-automatix-for-Canon Metz unit I bought when I was still using a DSLR.

    Note to self - must get round to selling the Metz.


    Anyway, I actually intended to add something useful here - I just remembered there's quite a handy webpage listing various flash voltages as measured by volunteers on't Internet; it can be found here http://www.botzilla.com/photo/strobeVolts.html
    Another day goes under; a little bourbon will take the strain...

  10. #20
    MattKing's Avatar
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    Quote Originally Posted by Steve Smith View Post
    One thing worth remembering is that all of these flashes were designed to work with all cameras. It is only recent paranoa with some digital cameras having low sync. voltage specifications which have brought up this worry.

    Pre-digital no one would have thought about sync. voltage and would have just used whatever flash they had with whatever camera they had.


    Steve.
    Steve:

    It is not just digital cameras that are susceptible. A lot of the more recent film cameras are as well. I've even be warned that my Mamiya 645 Pro could be damaged if I use it with something like my old Metz 202 or my old Bowens monolights..

    Matt

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