marcg Posted February 26, 2018 Share #1 Posted February 26, 2018 Advertisement (gone after registration) I hardly ever use flash – just very occasionally a bit of fill in in very bright backlit conditions. I've never used any flash with an M. As it happens I have FlashQ set of a transmitter and two receivers. For the first time I have just tried them out on an M10. I had thought that the camera would not trigger the flash over 180 but in fact I am finding that my M10 will trigger the flash at any speed including 1/4000. Is this normal? Is it simply that I just haven't understood how the flash system works on an M, or is this an unexpected result? Quote Link to post Share on other sites More sharing options...
Advertisement Posted February 26, 2018 Posted February 26, 2018 Hi marcg, Take a look here M10 and high-speed flash. I'm sure you'll find what you were looking for!
marcg Posted February 26, 2018 Author Share #2 Posted February 26, 2018 By the way, I haven't tried this with a high speed flash unit – just an ordinary one and so as I would expect, at 1/2000 there is only a strip of the frame which is properly exposed, 1/1000 a larger strip, 1/500 a much larger strip and finally 1/250 the entire frame is exposed. I have to find an old Metz flash which I have somewhere which can be set to something which will give a sufficiently long flash duration to expose the entire frame. I don't particularly understand why HSS needs to send out pulsed light when a single but longer flash might do the same job – but I'm really out of my depth on this – as you can probably tell. Simple explanations in simple English would be much appreciated. Ta Quote Link to post Share on other sites More sharing options...
Shadowplay Posted March 9, 2018 Share #3 Posted March 9, 2018 Flash duration is very short. Flash sync needs to occur when the shutter is 100% open or you get what you’re seeing where only a small portion of the frame is exposed because the flash fired when the shutter was partly open or closed. Quote Link to post Share on other sites More sharing options...
marcg Posted March 9, 2018 Author Share #4 Posted March 9, 2018 (edited) Thank you. Yes I understand that and in fact I understand that most HSS works by sending out pulses of flash each one timed to coincide with another section of the sensor being exposed so that in a way the photograph is being taken in strips. With a very fast exposure time, there is no single moment when the entire sensor exposed. With a very fast exposure time, the top of the sensor is already being covered at the time that the lower part of the sensor is being exposed. What I don't understand is why one can't simply have a very long flash – a single long pulse – which illuminates the subject during the entire explosion so that every strip of the sensor which is revealed has the benefit of the lighting. Edited March 9, 2018 by marcg Quote Link to post Share on other sites More sharing options...
Keith_W Posted March 9, 2018 Share #5 Posted March 9, 2018 What I don't understand is why one can't simply have a very long flash – a single long pulse – which illuminates the subject during the entire explosion so that every strip of the sensor which is revealed has the benefit of the lighting. The reason why is because flashguns can not vary the power of the flash. As in - it can not make the light shine dimmer or brighter. The only thing it can vary is the duration of the flash. With HSS, the flash strobes very fast. If you want less flash power, the flash strobes slightly slower. This is also why you always lose flash power with HSS. 1 1 Quote Link to post Share on other sites More sharing options...
jto555 Posted March 9, 2018 Share #6 Posted March 9, 2018 What I don't understand is why one can't simply have a very long flash – a single long pulse – which illuminates the subject during the entire explosion so that every strip of the sensor which is revealed has the benefit of the lighting. They do. http://www.priolite.com/en/home.html But the Priolite is only for off camera flash and needs its own trigger. http://priolite.lighting/control-a-hot-sync-leica/ Quote Link to post Share on other sites More sharing options...
marcg Posted March 9, 2018 Author Share #7 Posted March 9, 2018 Advertisement (gone after registration) Hmm, "explosion". Looks like my dictation software needs to be tweaked. Anyway, thank you for this information. I'm getting the impression that there are no workarounds for this unless one wants to spend a lot of money. I'm just an enthusiastic hobbyist so for me is just about satisfying a whim. Quote Link to post Share on other sites More sharing options...
RonM Posted March 9, 2018 Share #8 Posted March 9, 2018 What I don't understand is why one can't simply have a very long flash – a single long pulse – which illuminates the subject during the entire explosion so that every strip of the sensor which is revealed has the benefit of the lighting. As you stated, you do understand the need for a slow-ish shutter speed to expose the entire frame when using flash. If I under stand you correctly, what your are asking is, (with a very over-simplified example) if a flash duration is 1/2 second, and the shutter is opened for 1/1000 second, then why wont this work? At slower speeds this is referred to as 'dragging the shutter' and it adds ambient light to the scene, but I am not sure why it does not work at shorter shutter speeds, since the exposure would be over in 1/1000 second, so there would be no ghosting, and the full frame should be exposed to the flash's light. 1 Quote Link to post Share on other sites More sharing options...
marcg Posted March 9, 2018 Author Share #9 Posted March 9, 2018 As you stated, you do understand the need for a slow-ish shutter speed to expose the entire frame when using flash. If I under stand you correctly, what your are asking is, (with a very over-simplified example) if a flash duration is 1/2 second, and the shutter is opened for 1/1000 second, then why wont this work? At slower speeds this is referred to as 'dragging the shutter' and it adds ambient light to the scene, but I am not sure why it does not work at shorter shutter speeds, since the exposure would be over in 1/1000 second, so there would be no ghosting, and the full frame should be exposed to the flash's light. Yes. You understand me perfectly and have explained it brilliantly – much better than I could have done. I feel encouraged that somebody else doesn't understand why it can't work either! I've just been playing around with an off-camera flash set to expose at 1/2 second with a shutter speed of 4000, then 2000, then 1000 then 500 and it simply isn't working. Quote Link to post Share on other sites More sharing options...
RonM Posted March 9, 2018 Share #10 Posted March 9, 2018 Yes. You understand me perfectly and have explained it brilliantly – much better than I could have done. I feel encouraged that somebody else doesn't understand why it can't work either! I've just been playing around with an off-camera flash set to expose at 1/2 second with a shutter speed of 4000, then 2000, then 1000 then 500 and it simply isn't working. My only thought is if it is a TTL type flash, then it is sending out pre-flashes to determine exposure, and that may be confusing things. BUT, if it is a manual flash then I am not sure why it does not work. Quote Link to post Share on other sites More sharing options...
marcg Posted March 9, 2018 Author Share #11 Posted March 9, 2018 I have it set to manual. It is a Metz 48. I have no idea either Quote Link to post Share on other sites More sharing options...
Bunza Posted March 11, 2018 Share #12 Posted March 11, 2018 I think that there may be a bit of misunderstanding about the length of the flash. It might be me that is not understanding things but my understanding is that normal, electronic flash units have a very short duration of flash, 1/1000 up to 1/200 it would seem. It follows then, that with a focal plane shutter set at 1/250 second or faster the flash duration will be less than the time between the first curtain moving and the second one beginning its travel and staring to cover the sensor. This link to Wikipedia https://en.m.wikipedia.org/wiki/Flash_(photography) might help with understanding what is happening. Thanks to the previous posters, I think I understand the principles of HSS now. Camel Quote Link to post Share on other sites More sharing options...
marcg Posted March 11, 2018 Author Share #13 Posted March 11, 2018 I'm not sure that you have that quite correct. If you set the duration of the flash manually at 1/200 and you set the shutter speed 1/2000 then clearly the duration of flash will be 10 times longer than the duration of the exposure time and that should mean that at some point the entire sensor would have been exposed to light even if there is never a moment when the entire sensor is exposed at the same time. However, this doesn't seem to work. So far nobody on this thread seems to know why. 1 Quote Link to post Share on other sites More sharing options...
Luke_Miller Posted March 12, 2018 Share #14 Posted March 12, 2018 (edited) To Recap: It is not possible to control the duration of the flash (except via High Speed Sync). Flash duration typically varies a bit depending on the flash power setting, but is not otherwise user controlled. So the flash part of the exposure will always be something like 1/1000 second. Unlike a leaf shutter, a focal plane shutter's max flash sync speed is a function of the shortest shutter speed in which the entire sensor (or film gate) is exposed. Depending on camera that speed can be 1/180, 1/200, or 1/250 second. At shorter durations the rear curtain must start its travel before the front curtain has finished. This means that the flash part of the exposure completes while part of the sensor is obscured by one of the curtains, creating a dark band in the image. When High Speed Sync is employed the flash emits a rapid series of pulses so that the flash part of the exposure now extends for the duration of the shutter curtain travel. This greatly reduces effective flash power, so is useful only for relatively close distances. This focal plane sync limitation is why cameras intended for studio work typically have a leaf shutter option. Edited March 12, 2018 by Luke_Miller 1 Quote Link to post Share on other sites More sharing options...
marcg Posted March 12, 2018 Author Share #15 Posted March 12, 2018 I understand what you're saying, but I still don't understand why an off-camera flash unit can't be forced to produce a flash duration which is set manually by the photographer and that this can be different from the shutter speed set on the camera. As far as I'm aware, the camera simply sends a signal out to the flash unit to instruct it to flash. After that, if the flash unit is set to manual then it will act according to its settings. If the flash is set for a duration of 1/200 and the camera is set to a shutter speed of 1/2000, are you saying that regardless of the manual setting, the duration of the flash will still be controlled by the camera? Quote Link to post Share on other sites More sharing options...
LocalHero1953 Posted March 12, 2018 Share #16 Posted March 12, 2018 (edited) Marc, what are you setting on the flash? What mode is it set to, and what parameter are you changing? I don't want to add to the confusion, but..... I've looked at the user guide for the Metz 48, and it seems you have two available modes: M and M-HSS. For M mode there would be nowhere for you to set the flash duration. The table at the end of the guide gives the flash duration at each power setting - 1/125s at full power, reducing to 1/25000s at minimum power. So I'm not sure how you are 'setting' a duration of 1/2s! The user guide is reticent about M-HSS mode and how you control it manually (and I don't have the Metz 48 to look at). If you set this mode does the flash allow you to manually enter the Leica's shutter speed? I wouldn't expect it to need this information: all it is doing is pulsing for as long as the shutter takes to sweep across - the normal slow sync speed of the M10 (1/250s??). Remember the flash will have no other means of knowing what the Leica's shutter speed is, and the Leica will not know it is trying to sync HSS. Basically, unless the Leica has a Leica flash on top, all it is doing is sending a trigger signal to the hotshoe, whether or not there is anything to trigger. Edited March 12, 2018 by LocalHero1953 1 Quote Link to post Share on other sites More sharing options...
marcg Posted March 12, 2018 Author Share #17 Posted March 12, 2018 Thanks for this. I haven't tried the HSS mode because I'm quite sure that there is no communication between the camera and the flash and that the use HSS mode there has to be some exchange of information. This is what you suggested and I completely agree. I've been trying the manual mode and frankly it was some time ago and I can't remember what I did – but it didn't work. I'll try again over the next few days and tell you exactly what I'm doing. It's not important to me in the sense that my photography doesn't depend on it. I just thought it would be neat if it could happen and might give me some more ideas about what I could do Quote Link to post Share on other sites More sharing options...
Bunza Posted March 13, 2018 Share #18 Posted March 13, 2018 This may help. From the M10 manual : “With the conventional time for firing the flash, at the beginning of the exposure, i.e. immediately after the 1st shutter curtain has completely opened the sensor window. This can actually lead to apparent contradictions, e.g. in the picture of a vehicle, which is being overtaken by its own light trail. The camera allows you to choose between this conventional firing moment and synchronization with the end of the exposure, i.e. immediately before the 2nd shutter curtain starts to close the sensor window again. In this case, the sharp image reflects the end of the movement captured. In the photograph, this flash technique gives a natural impression of movement and dynamics.” When using a conventional/non-HSS unit, ie single flash/pulse of light, with a shutter speed faster than the synch speed of the camera (even if the flash duration is longer than the synch speed) there will be a portion of the sensor that will not receive light light from the flash as the second curtain will have started moving and will have covered part of the sensor before the flash fired. Using rear curtain synchronization will not help as the flash will not fire until shortly before the end of the exposure and by then part of the sensor will have been covered by the second curtain. An HSS flash unit facilitates the use of shutter speeds faster than the synch speed by providing multiple high-speed short-duration flashes that are synchronised to “follow the slit” as it travels in front of the sensor; the multiple flashes start before the first curtain has reached the end of its travel and continue until the second curtain has completed its travel. A long duration single pulse from a conventional flash can never light the entire sensor when the shutter is set higher than the maximum synchronization speed as it will never fire until the first curtain has reached the end of its travel by which time the second curtain will have covered part of the sensor or, if using rear curtain synchronization the flash will fire as the second curtain reaches the end of its travel and again part of the sensor will already have been coverered. Therefore, unless the flash fires before the shutter is relased it is not possible to have light from the flash reach all of the sensor. Camel Quote Link to post Share on other sites More sharing options...
RonM Posted March 13, 2018 Share #19 Posted March 13, 2018 This may help. A long duration single pulse from a conventional flash can never light the entire sensor when the shutter is set higher than the maximum synchronization speed as it will never fire until the first curtain has reached the end of its travel by which time the second curtain will have covered part of the sensor or, if using rear curtain synchronization the flash will fire as the second curtain reaches the end of its travel and again part of the sensor will already have been coverered. Therefore, unless the flash fires before the shutter is relased it is not possible to have light from the flash reach all of the sensor. Camel Agreed, but what the OP asked is if the duration of the flash is LONGER than that of the shutter speed, why doesn't the exposure come out correctly? 1 Quote Link to post Share on other sites More sharing options...
sillbeers15 Posted March 28, 2018 Share #20 Posted March 28, 2018 I have successfully made a manual flash to fire at off camera position via triggering the slave sensor at 1/5000 sec with the following steps: 1. The manual off camera flash must be set to optical flash mode and 1/1 power; 2. The triggering flash mounted on camera must be a Leica TTL compatible flash and set to TTL ( SL & M10) as the camera has no setting for HSS. Quote Link to post Share on other sites More sharing options...
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