How fast will my LF lens sync?

Discussion in 'Large Format Cameras and Accessories' started by Prime, Sep 27, 2002.

  1. Prime

    Prime Member

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    I have a Nikkor 90mm f/8 lens. The shutter (Copal #0) goes up to 1/500. If I use it with flash or strobe will it sync at 1/500, or is there another widely-used shutter speed? Thanks!
     
  2. Jorge

    Jorge Inactive

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    It will sync up to 1/500. Flash is much faster than shutter speed and since you are opening the shutter completely when you actuate it, the film will get fully exposed. Sync speed with LF is usually better to control the amount of ambient light you want in your shot.
     
  3. HuwEvans

    HuwEvans Member

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    Flash isn't always that fast - only at low or mid-range power. At or near full power some units have quite long discharge times - longer than 1/500th at any rate. At full power my Metz 45CT3 has a discharge time of 1/300th, and I think (although I've never measured them) that my studio monolights are even longer than that.

    OTOH, although the Copal 0 shutter speeds go up to 1/500th, there is a fair chance that they will be rather slower than that, so it may not matter in practice.
     
  4. Thilo Schmid

    Thilo Schmid Member

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    A leaf shutter has sync on all speeds. A focal plane shutter on the other hand, usually has a max. sync speed that is much slower than its fastest speed. Both, your leaf shutter and your flash are not “digital” in their operation. Light intensity increases as the leaf shutter opens and decreases as it closes. When the flash is triggered, it rapidly reaches its peak light volume and then “burns out”. Both processes take place within fractions of a second and usually cannot be observed with the naked eyes. While the focal plane shutter has a very small time-window when both curtains are open, the flash light might not have finished when the second curtain start to close. This is not the case with a leaf shutter. Although a leaf shutter may cut the flash, too, the effect will be an underexposure but not a partial exposure as it would happen in case of the focal plane shutter.

    The specs of a studio flash usually contain one or two of the figures “t 0.1” and “t 0.5” (usually for max. load). These figures specify the amount of time the flash needs to reach 1/10th (or 1/2 respectively) of its maximum intensity after being fired. The values for t0.1 can be as long as 1/60s for very powerful flashes and is usually shorter than 1/500s for lower energy or compact (battery) flash lights.

    The shutter speed is usually determined by the desired amount of ambient light in the scene. The longer the shutter speed the more weight is on ambient light, as long as the flash energy stays the same.
     
  5. Prime

    Prime Member

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    Thanks, all.
     
  6. steve

    steve Member

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    One of the problems with a leaf shutter is acceleration and deacceleration of the shutter blades. Obviously, the shutter cannot open or close instantaneously because it has mass. If you look at a graph of a leaf shutter opening and closing, it ramps open (slopes up) had a flat open period, and then ramps down to close.

    The exposure period is the total time from the beginning of the edge of the ramp until the trailing edge of the closing ramp. Lenses with leaf shutters have a built in delay (for electronic flash - X-sync) to time the flash to compensate somewhat for the shutter not being completely open when the flash is triggered.

    Here's the problem. The faster the shutter speed you are using with a flash, the greater the exposure problem as leaf shutters are notorious for being inaccurate as they near the peak shutter speeds. Also, the larger the shutter, the greater the problem because of greater mass, etc.

    My advice is to expose at 1/60th second or less using an electronic flash with a leaf shutter because you actually control the light reaching the film with the aperature setting (in most cases) - and the shutters are far more accurate in speed at lower shutter speed settings.

    If you use fast shutter speeds 1/125, 1/250, 1/500, you may find yourself using a larger f/stop or higher flash power setting to compensate for under exposure caused by the shutter open/close cycle.
     
  7. HuwEvans

    HuwEvans Member

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    Steve, I think you're confused about the way that leaf shutters sync. The sync is achieved by a switch that closes the circuit across the PC connection, and is physically tripped by the blade mechanism as the shutter reaches the fully open position. Thus the time required for the shutter to open has no relevance - only the time it stays fully open matters. There is certainly no need to restrict yourself to 1/60th or slower.
     
  8. George

    George Member

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    The truth is that most shutters are not able to have the optimum synchronization on the whole scale of their shutter speeds. At both ends of the scale they are deficient, more or less. If well synchronized at the slow end they will lack light at the highest speeds and vice versa. Only special shutters with a fully adjustable delay are synchronized at all shutter speeds (that is the original meaning of the expression "a fully synchronized" shutter).
     
  9. steve

    steve Member

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    With all deference to your Huw-ness, I will render the following on leaf shutter synchronization.

    First, I don't take camera equipment or watches apart as I seem to have a better talent for losing small parts than reassembling the item. So, I have not personally ever taken a large format shutter apart to see or test how it synchronizes - nor do I intend to for the above stated reason.

    Secondly, I can only go on what I was taught in photo school, the information in my photo books, and 35 years of experience.

    What Stroebel says about synchronization is as follows:

    "It is sometimes assumed that because of the short duration of the light from electronic flash tubes, none of the light can be cut off by the shutter and the guide number will remain constant at all exposures."

    "...makes it possible for the shutter blades to close soon enough to prevent some of the light from reaching the film. A test made with one type of electronic flash unit revealed that only 59% of the light was transmitted at 1/500 of a second compared to 1/100 of a second and slower speeds..."

    "Changing the exposure time setting from 1/30 second to 1/500 second reduces the light from a continuous source to approximately 1/17, but reduces the light from flash lamps to approximately 1/4."

    Lastly, all shutters (focal plane or leaf shutters) have a built-in synchronization delay. With a leaf shutter, it can be as long as 30 milliseconds. What the designers are trying to do is get the shutter to the fully open portion of the total shutter open/close cycle before the flash is triggered as you stated. This requires a delay.

    My point being that unless the shutter has a continuously variable delay (most that I know of don't do that), you are better off to use slower shutter speeds with an electronic flash. Or, you will need to do testing to see the change in exposure caused by the faster shutter speed.

    Heck, I could be wrong, Leslie Stroebel could be wrong, the Langford Manual of Photography could be wrong - but...

    This has been borne out in my own inadvertant (OK- mistake) electronic flash exposures. When the shutter was set at 1/250 with the correct f/stop, the transparency appeared about 1/4 stop under exposed. When I changed the shutter speed to 1/15 second with the same f/stop of the same subject it was correctly exposed.

    However, as someone once said, "your mileage may vary with usage..."
     
  10. HuwEvans

    HuwEvans Member

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    As I said earlier when a flash is working at high power output its discharge time can be longer than the faster speeds on a leaf shutter. Thus the shutter begins to close before the end of the flash. This appears to be what Stroebel is talking about, and is probably what you have experienced. However, for virtually anything other than full power output most flashes have much shorter durations that the fastest speed of typical leaf shutters, and will be unaffected.

    I reiterate, for electronic flash the sync is triggered by the shutter blade mechanism reaching the fully open position. In other words, the delay you refer to is not something independent of the shutter blades, but is actually part of the same system. This is a direct mechanical linkage and provided the shutter is not faulty there is no way that it can fire the flash before this point. For M-sync it is a different matter. Here the flash is triggered at the beginning of the opening phase and the time to open may indeed have a bearing.
     
  11. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I think Huw has it right. This has always been my understanding of how the sync works in a leaf shutter.

    In any case one only needs speeds faster than 1/125 s. when ambient light levels are very high, as in bright sunlight, or if one were using an extremely low power flash, perhaps to stop action. With normal strobes in ordinary room light all at conventional levels, it would be unusual that the strobes would not be at least four stops brighter than ambient.
     
  12. steve

    steve Member

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    " In other words, the delay you refer to is not something independent of the shutter blades, but is actually part of the same system. This is a direct mechanical linkage and provided the shutter is not faulty there is no way that it can fire the flash before this point."

    There is NO misunderstanding with how a shutter works. What you have posted is exactly what I said - but, it is a delay from the time the shutter is first triggered - whether is directly mechnically linked or not. On one of my older lenses, I have several sync positions for different types of flash bulbs plus an "X" sync for electronic flash. I assume that a different gear train is engaged to vary the delay to trigger the flash bulb sooner (shorter delay) than at "X" sync in order to let the flash bulb reach peak illumination when the shutter is fully open - and take into account how long it is illuminated. Change types of flash bulbs sync delay is changed to account for time it takes the bulb to get to peak illumination and how long the bulb actually burns.

    My only reason for posting is to alert Prime that IF he uses a fast shutter speed with an electronic flash under certain circumstances he may underexpose the film. So, if he gets under exposed film with a correctly set f/stop and flash power setting, the cause could be because of a high shutter speed - and not some mysterious force from the planet Saturn, the moon being out of alignment with his horoscope sign, a problem with his camera, or not wearing his aluminum helmet at the proper angle to protect himself from aliens....

    At this point - I think we're beginning to beat that proverbial dead horse.
     
  13. HuwEvans

    HuwEvans Member

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    Steve, I'm sorry if you think I have misinterpreted you, but your initial post on this subject did very explicitly state that, 'leaf shutters have a built in delay (for electronic flash - X-sync) to time the flash to compensate somewhat for the shutter not being completely open when the flash is triggered'. This is simply untrue, because the way that leaf shutters work means that the blades are always fully open when the flash is triggered.

    You went on to say that, 'the faster the shutter speed you are using with a flash, the greater the exposure problem...' Well, this is true, but only because the flash may be too long in duration for the open time of the shutter. It has nothing at all to do with the acceleration/deceleration times of the shutter blades. It would be true even if they could open or close instantaneously, and in fact the problem would be worse if that were the case.

    You also said, 'the larger the shutter, the greater the problem because of greater mass, etc.'. I'm sorry, but no. Large shutters do indeed take longer to open and close, and this is why, for example, Copal #3 shutters have 1/125th as their fastest speed. But it does not affect flash sync.

    Finally you said, 'my advice is to expose at 1/60th second or less using an electronic flash with a leaf shutter'. I'm sorry if it upsets you but I think this is bad advice, and it is the main reason I posted a follow-up. Only when using very high flash powers is it necessay to use slower shutter speeds, and that only for the reasons stated earlier, and it would be true regardless of what type of shutter was in use. For most handheld units you can safely use shutter speeds up to 1/500th with leaf shutters almost all the time, without any danger of the shutter itself cutting off the flash before it is fully discharged. For a few handheld units and for studio flash at higher power settings it may be necessary to stick to shutter speeds of 1/250th or possibly 1/125th and slower. To use speeds of 1/60th or slower whenever using flash is quite unnecessary, and squanders one of the main advantages of leaf shutters.
     
  14. steve

    steve Member

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    Gee...you know we're both writing in English but not communicating. I'll try waving my hands on this one.

    First let's define "delay." That is the time from the moment the shutter is released until the flash is triggered. The flash on a leaf shutter is NOT triggered immediately upon shutter release, so by definition there is a delay. OK??

    When you release a leaf shutter, there is a gear train connected to a spring drive gear mechanism that provides flash synchronization. This gear train is the "delay mechanism" AND the sync mechanism in the shutter. Gears have to turn a certain distance (delay) before the flash is triggered (trigger mechanism). If you would like confirmation of the sync gear train, please get a service manual for a Compur or like shutter and you will see the part numbers for the flash synchronization gears, etc.

    The flash is not triggered by the blades reaching the open position but by the gears and how far they have turned, which MOSTLY corresponds to the position of the blades being fully open - but, does not EXACTLY correspond to the fully open position at ALL shutter speeds. There are inaccuracies inherent within timing of the gear train trigger mechanism versus shutter speed setting.

    Hence the information from Stroebel about the flash being measured as 59% less at 1/500th than at 1/100 or less - something YOU seem to want to ignore - actual tested, and documented results by a recognized expert in the field of photography and photo science. Not an opinion, not conjecture, not speculation - documented facts.

    As for exposing at 1/60 or less - yes that's still my advice if you are using manually set power levels and NOT an automatic flash with a quench circuit - AND you have a shot that cannot be easily duplicated. When you talk about long flash exposure times only at full power you are both correct and somewhat wrong. If the flash uses a quench circuit then yes, the flash duration gets rapidly shorter than the longest duration at full power because you are using a fully charged capacitor, and stopping the current when the appropriate exposure has been reached.

    With this type of flash operation, flash speeds can be as short as 1/10,000 of a second. Most flashes with quench circuits will not go faster than 1/10,000 as when the flash time gets shorter than that, you can have a problem with reciprocity (failure of the law of reciprocity) just like you do with long exposure times.

    Now, if you use a flash that allows power variation (1/2, 1/4 power, etc.) the duration is not effected nearly as much as the quench circuit limiting the exposure, because you are only discharging a partially charged capacitor. Using a flash in this mode rarely approaches a flash time of 1/1000 of a second.

    My personal flash usage is mainly with large power packs (3000 watt/second ratings) and multiple flash heads in architectural photography. And yes, I have to run nearly everything at full power with multiple heads being used on a lot of occasions where I am not attempting to only provide fill for daylight, but fully illuminating an entire scene.

    I rarely use a hand-held unit with thyristor quench circuit. As I stated previously, I have noticed under exposure using 1/250th of a second or higher shutter speeds and my strobes - hence, my comment about "your mileage may vary." Meaning, your personal equipment AND usage may NOT create this problem. Is that clearly understood? This is not a hard and fast edict for everyone. It is a problem that I have had and have documented as being related to the shutter speed. Not and equipment problem, not an exposure miscalculation, not a strobe problem, the shutter speed was too short.

    You are correct, not everyone will have this problem, but my point is if you are doing flash photography using leaf shutters - YOU SHOULD KNOW ABOUT THIS AS A POTENTIAL PROBLEM. Your approach seems to indicate that it will NEVER be a problem. This is forum allows educational opportunities - I chose to point out a documented anomoly inherent within leaf shutter / electronic flash usage under certain circumstances.

    My advice should have been - test your equipment under a variety of operating conditions, including power levels, and shutter speeds as underexposure is a real potential problem with certain flash / shutter speed combinations. Does that suit you somewhat better?

    And, I too am sorry if you don't like my recommendations which are based on both photo science documentation AND personal experience - and MY ONLY POINT BEING (again, apparently ignored by you) - is that:

    >>>IF<<< someone has underexposed flash photos

    >>>AND<<< they are using a high shutter speed with a leaf shutter,

    >>>THEN<<< it may be BECAUSE of the high shutter speed,

    AND NOT AN ACCIDENT, OR MISCALCULATED EXPOSURE.

    I'm truly sorry IF YOU don't get that simple message.
     
  15. b.e.wilson

    b.e.wilson Member

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    Hi Steve. While it is true that your last post said nothing new, it simply being the most amazingly detailed reiteration I've ever seen, I do have a very slight problem with your 1/60 sec recommendation. I think that Kodak's recommended X-sync speed of 1/125 is probably a little better at lessening the possibility of ambient-light 'ghosts' than 1/60 sec would provide. Depends on the amount of ambient light, so your milage may vary ;-)

    Having said that, I have an old shutter that just isn't up to snuff any more, and needs a speed of 1/50 sec or longer to work right. When the temperature drops below 50 F I can set it on anything; it slows down to the point that it gives second-long exposures every time.

    I personally like to use flash in a manner that emphasizes natural light as much as possible, so when a flash is needed I typically have many-second-long exposures, and fire the flash manually, or (rarely) paint the scene with light. But in the end I don't use the flash much, so I will always concede any point made by someone more experienced with flash than I.
     
  16. George

    George Member

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    Thanks Steve for the detailed explanation. I have a great deal of respect for Stroebel too - even if I don't have any problem of synchronizing even at 1/500 s. But that is for macro work and short distances with automatic flashes.
     
  17. HuwEvans

    HuwEvans Member

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    Steve, after this reply I am not going to waste any more time on this point, so you can have the last word if you wish.

    You refer to the gear train and main spring drive mechanism - this is what drives the entire shutter - blades, as well as the flash sync. These last two are connected mechanically in a way which does not allow slippage or variation in the position of the blades at the point when the flash is triggered - unless, as I said before, the shutter is faulty. And I am not talking about general wear and tear, but a serious fault. Apart from this circumstance it is not possible for the flash to trigger before the blades reach the fully open position. Like it or not, this is a fact.

    You keep on citing Stroebel, but nothing you have quoted is at all inconsistent with what I have been saying. Problems occur when the shutter begins to close before the flash has finished (and, yes, I know that flash output is not always a good approximation of a step function). This is true for all types of shutter, not just leaf shutters, and, contrary to your original reasoning, would be true even if the shutter were capable of opening or closing instantaneously. It is also rather obvious.

    I can quite imagine the 3KJ packs you use would create a problem with speeds over 1/60th, but your advice related to electronic flash in general, without that qualification - a wholly unreasonable restriction. Furthermore, the problem has nothing whatever to do with the explanation you gave. Leaf shutters will indeed sync correctly at any speed, but sometimes a flash may be too long for the shutter speed selected - a point I made clear in my original post on this thread.

    With that, I am out of here.
     
  18. George

    George Member

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    " It is not possible for the flash to trigger before the blades reach the fully open position".
    HuwEvans, you are very much mistaken. As Stroebel has it - "Flash-synchronized shutters are designed to close the electrical circuit to the flash at the appropriate time so that the shutter will be fully open when the flash reaches its peak light output". It is for this very reason that the flash is triggered BEFORE the blades are fully opened so that the light peak - comming later, i.e. with a delay - can reach the fully open blades (hopefully, but not always). Stroebel speaks clearly about this, even figures showing the delays are provided by him.
    "Like it or not this is a fact".
     
  19. b.e.wilson

    b.e.wilson Member

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    Without a more complete rendition of the quotation (until I get home and can look it up), I'm hesitant to accept Stroebel's quote, as he might be speaking of M-synced flash (the setting used for magnesium-wire flashbulbs). Bulbs must be triggered before the shutter is opened to allow the burning reaction to get going.

    That being said, I think that shutters are made with a little slop in the flash-triggering mechanism. The greatest opening force, applied through the shortest and most controlled lever arm, is applied to the blades to get them moving. At the end of the opening sequence the lever arm is lengthened (to provide more velocity) which means the opening force is much diminished, and the mechanism relies on the inertia of the blades to achieve the full-open position. I suspect (without evidence) that if the blades had much friction, as they might in a horizontal position, that the full open position would be slowed, even though the opening mechanism was at its fullest extension.

    But even if this is so, it would only affect exposure at the widest aperture. For typical, stopped-down shots, the effect on the exposure would be none, none...more black.

    And herewith I officially enter myself as a belligerent in this thread.
     
  20. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I have to agree. That quote sounds like a precise description of M-sync flash. If you look at some old shutters like this Ilex pictured on S. K. Grimes' website:

    http://www.skgrimes.com/ilex/ilexbig/sidebig.jpg

    you'll see there are numbers for different flash sync settings. These refer to the number of milliseconds in advance of the full opening of the shutter required for synchronizing different types of flashbulbs. For X-sync, one sets the shutter on the "0" setting, so that the strobe fires precisely when the shutter is wide open, not before, because the peak is virtually instantaneous. The only relevant concern here is for studio flash units, which might actually have a longer duration at full power than the shutter speed.
     
  21. HuwEvans

    HuwEvans Member

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    I didn't intend to reply again on this matter, but since someone else is now having a go at me I suppose I have to. Hopefully this will be the last time. Once again, if George wishes to have the last word he is welcome to it.

    George, Stroebel can say what he likes. 'M' synchronization occurs before the fully open position because bulbs took a relatively long time to build up to their maximum output, but electronic flash is much, much faster. Conventional leaf shutters are designed to trigger electronic flash at the point where the shutter blades reach the fully open position. (If you really don't believe me I suggest you dismantle a few sometime - you will find it very instructive, and provided you take care with it it is really not as difficult as many suppose.)

    If you want to be really picky it is just possible that the circuit might be closed a minute fraction before, but certainly not so as the blades are still partially covering the aperture (even at its maximum) - so the shutter is, in every meaningful sense, fully open.

    If this were not the case low power flash bursts (which may be effectively over within a few 1/100000ths of a second) would be spent before the shutter had fully opened. As it is though, any synchronized shutter which is working normally will be perfectly okay with the shortest of flashes even at their typical highest speeds of 1/500th.
     
  22. George

    George Member

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    I strongly suggest to all those that think that Stroebel has said someting else than he said to take his book and to learn about the flash synchronization from him. View camera technique, Leslie Stroebel, 5th. edition, Focal Press, p.68-72. Without reading it you can make teories about what he said or didn't say but they are totaly useless for those who read what is said and what isn't said. A lot of diagrams about the different delays and synchro problems are there too...
     
  23. Ken Burns

    Ken Burns Member

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    I have followed this thread with interest. I would like to add my comments. I own an old Alphax Synchromatic that discharges my studio flash before the shutter blades have reached the fully open position. This can be easily observed by looking into the lens while the shutter discharges the flash in a darkened room. As long as I stop this lens down to f/8, this problem is not an exposure issue, but if the lens were left opened to the widest aperture, f/5.6, it would be. I can say with confidence that with this particular shutter, the shutter blades definitely do not have to reach the fully opened position for the flash to discharge.

    This old shutter does have both X and M sync settings, but there is no problem with my having used the incorrect setting. If the M setting is used, my flash fully discharges before the shutter even begins to open. This problem of discharging the flash too soon, exists at all shutter speeds including B and T.

    It is very easy to see if the shutter has opened when the flash discharges, and theoretically one should also be able to determine if the shutter has closed before completion of the discharge. Just look into the lens as the shutter is tripped, and if you do not see the shutter in both the opened and then closed positions during the brief flash of light, the flash duration is definitely longer than the exposure time. Optimally, one should be able to see the shutter only in the fully opened position.