Another flash sync query

[swifty]

Assuming there is no FP mode, is it possible to get the camera to sync with an off-camera flash at shutter speeds higher than the max sync speed?
I've only been using Nikon's CLS system so I'm not familiar with how other brands work and max sync speed in general.
When in manual everything mode and using a radio trigger of some sort, can you manually set up the exposure with a shutter speed higher than the stated max flash sync and still have your flash light your subject without any part of the shutter curtain showing up in the frame?

Eg.1 lets say you're outdoors in bright daylight and you set your exposure for the background and you require a high shutter speed but your subject is in the shadows to be lit off-camera by a brolly or softbox. Will the flash duration be long enough such that you can still expose your subject provided you up the intensity of the flash to compensate for the shorter duration of the shutter or won't it sync at all.

Eg.2 lets say you wanted to freeze a subject in motion with an off-camera flash. Do you do it with the shutter speed or does the flash duration do the 'freezing' so to speak. Assuming the subject is only lit by the off-camera flash and ambient light plays no part.
If its flash duration, how do I find out or ctrl how long the flash duration lasts?
If its the shutter speed, same question as above in eg.1 - is there a way to still sync past the max flash sync speed?

[I @ M]

Swifty, in general and as a short answer, no it isn't possible to get a flash working at a faster speed than the synch is rated.
There are quite a few factors at play with your questions and I will share my very much non expert thoughts.
Starting in a totally random order --- Flash duration plays a large part in being able to synch with a camera at even the maximum advertised speed. There are a few technical explanations around that show things like sine waves and other magical phenomena but as I gather it, the shorter the flash duration the faster the shutter speed that can be obtained. For instance Nikon are claiming a max synch speed of 1/320 in high speed fp in newer models and apparently that is easily achievable with the SB900 but less doable with earlier speedlights. From what I have read, to obtain the shortest possible flash duration the flash needs to be at a fairly low power level. That part may partly answer your thoughts on freezing moving subjects with little ambient light, flash duration combined with a (relatively) fast shutter does the work. As far as I know there is no way of controlling the flash duration of a speedlight or most common monobloc heads. If you read around the various manufacturers, many will show the flash duration of their units and some of the very expensive ones have very fast figures attached to them. I know from my own mucking around at home here that the two old Courtenay monoblocs have a relatively long flash duration and I am hard pressed to get 1/200 synch with radio triggers but I can most of the time get 1/250 triggering them with the onboard flash. That brings the radio versus optical trigger into the mix. Simply, light travels faster than radio signals so the problem compounds itself. However I have a theory that when triggering through a hot shoe connection on a Nikon that there is a programmed time difference for the actual signals being sent if that makes any sense.
As a bit of proof of my theories, I do get better results with an inexpensive Chinese monobloc as it appears to have a shorter flash duration than the older Courtenay heads and from memory the advertising for that Chinese head claimed around the 1/800 flash duration. Apparently theses days, 1/800 is not particularly fast either.
There are several other factors that come into play which influence synch speed. Once again I will have to talk about Nikon as I haven't looked into other brands. Apparently a lot of the Nikon bodies "know" when a flash or trigger is connected via a hotshoe mount and make the camera work accordingly and then there are other models that don't "know" that a connection exists but still trigger anything attached at the press of a shutter.
Here is the interesting part, our D50 which has a rated synch speed of 1/500 sec will reliably trigger the Chinese flash head , via onboard flash or radio trigger at 1/800 sec. There as a far as I can figure out, two things that make that work, firstly the D50 is a model that doesn't "know" that a flash is attached and secondly, along with many of the other entry level or lower specced cameras in the Nikon range it has a different shutter operation where the curtain/s open slightly faster but also stay open longer and the sensor actually turns on and off during the period of time that the curtain/s are open. To me it makes perfect sense that if the curtain/s are not moving during the duration of the flash then they will not show in the picture and add that to the fact that an electronic switching on and off of the sensor is going to happen very quickly so therefore higher synch speeds are possible.

Further education:D

Read at the strobist blog spot (http://strobist.blogspot.com/).
DesmondD (http://www.ausphotography.net.au/forum/member.php?u=7283) has some very good insights into lots of things dealing with Nikon flash systems on his blog. He understands things electrical. :D A couple of very good articles are here (http://desmonddowns-ttlblflash.blogspot.com/2010/01/realsynch-flash.html) and here (http://desmonddowns-ttlblflash.blogspot.com/2010/01/high-fp-flash.html).

[swifty]

Thanks Andrew for that info. I don't have time to respond now cos I gotta get ready for work (sat work s$*cks) but will do so later n have a read of the links u provided.
Cheers
Dave

[DesmondD]

DesmondD (http://www.ausphotography.net.au/forum/member.php?u=7283) has some very good insights into lots of things dealing with Nikon flash systems on his blog. He understands things electrical. :D A couple of very good articles are here (http://desmonddowns-ttlblflash.blogspot.com/2010/01/realsynch-flash.html) and here (http://desmonddowns-ttlblflash.blogspot.com/2010/01/high-fp-flash.html).

Yeah , who needs that stobist blog :D
With a Nikon D40/50/70 you can do wireless flash at 1/4000th sec (http://desmond-downs.blogspot.com/2010/01/14000th-sec-wireless-flash-synch.html) .
This weekend I did some tests with the SB800 and SB26 in their "SU-4" modes (http://desmond-downs.blogspot.com/2010/04/flash-su4-wireless-trigger-working.html) - I was using my D50 and an old SB24 to trigger them and got speeds of 1/4000th sec as well .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zsu42nd011.jpg

http://i107.photobucket.com/albums/m300/dvdowns/Flash/zsu42nd023.jpg

But this is only with these cameras [ D40/50/70 ] that have en electronic shutter/sensor so if you want superior performance you may need to get a D40 :th3:


.

[swifty]

Hmm..
if the flash duration was shorter than the shutter speed and the shutter was fired at a speed slower than the max sync, then it makes sense that whilst the shutter is completely open, the entire frame is exposed by the full duration of the flash. At a higher speed than the max sync, then I guess the camera can't co-ordinate the flash and shutter to fire together.
But if the flash duration is a lot longer, eg. instead of something quite high like 1/1050th of a second (SB800 at full power), say it was around 1/200th a second then wouldn't the flash be firing over the entire time the shutter is open when the shutter speed is quicker than 1/200.
Of course because the shutter speed captures a smaller fraction of the time the flash fires then the output would be less.
But since we can't change the flash duration, lets take 1/1050th of a second for the SB800 firing at full power. If the shutter speed was greater than 1/1050th ie. the whole time the shutter is open the flash is also firing, shouldn't the whole thing sync??
Is this essentially not what FP mode does, fires a continuous burst of flash at lower power (effectively increasing the duration of the flash but lowering the power)?
BTW.. I thought that radio waves also travels at the speed of light??

Actually I was trying to figure out the practical limitations of the m43 system as opposed to the Nikons because m43 currently only have a max sync speed of around 1/160th of a second I believe and no FP modes. So wondering if there were work arounds should u need higher shutter speeds.

Cheers

[kiwi]

In fps the flash pulses in sync with the shutter so ad to achieve output without banding at higher than the sync speed. A dramatic loss of power is apparent as a result

Useless answer to your particular problem I know


Sent from my iPhone using Tapatalk

[DesmondD]

Hmm..
if the flash duration was shorter than the shutter speed and the shutter was fired at a speed slower than the max sync, then it makes sense that whilst the shutter is completely open, the entire frame is exposed by the full duration of the flash. At a higher speed than the max sync, then I guess the camera can't co-ordinate the flash and shutter to fire together.
But if the flash duration is a lot longer, eg. instead of something quite high like 1/1050th of a second (SB800 at full power), say it was around 1/200th a second then wouldn't the flash be firing over the entire time the shutter is open when the shutter speed is quicker than 1/200.
Of course because the shutter speed captures a smaller fraction of the time the flash fires then the output would be less.
But since we can't change the flash duration, lets take 1/1050th of a second for the SB800 firing at full power. If the shutter speed was greater than 1/1050th ie. the whole time the shutter is open the flash is also firing, shouldn't the whole thing sync??
Is this essentially not what FP mode does, fires a continuous burst of flash at lower power (effectively increasing the duration of the flash but lowering the power)?
BTW.. I thought that radio waves also travels at the speed of light??

Actually I was trying to figure out the practical limitations of the m43 system as opposed to the Nikons because m43 currently only have a max sync speed of around 1/160th of a second I believe and no FP modes. So wondering if there were work arounds should u need higher shutter speeds.

Cheers

Here's the back of an old Canon film camera with a flash synch speed of 1/90th sec .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/highfpvid008t.jpg

Here's the same shutter at 1/1000th sec with an old Nikon flash on top - the camera didn't know a flash was attached and so allowed the higher shutter speed .

http://i107.photobucket.com/albums/m300/dvdowns/Flash/highfpvid011t.jpg

That's quite a skinny slit [ I'm not saying the newer digital cameras are exactly the same though ] and even with a relatively long flash duration that slit is going to take a while to travel across the screen .
Maybe sometime soon I will try it with my D90 and the SB24 at 1/1000th and see how much travel it gets at 1/1000th .

I did some tests with the Yongnuo RF602 (http://desmonddowns-ttlblflash.blogspot.com/2010/02/yongnuo-rf-602-wireless-flash-trigger.html) trigger and could achieve flash synch up to 1/800th sec at 100m with my D50 . Although radio waves travel very fast I suppose there are limitations to the switching times of electronic circuits especially if , perhaps , a capacitor was involved that needed time to charge for some reason .


.

[farmer_rob]

Firstly, radio waves do travel at the speed of light - they are the same form of radiation, just lower frequency than light.

Secondly, as I understand it, the problem is changing from CCD to CMOS sensors - you could use a form of electronic shutter on the CCD, which you can't on the CMOS sensor. This has the effect of lowering the point where the shutter needs to change to a moving slit.

Thirdly, I'd guess that if the flash duration is longer than the shutter time when it is above sync speed, you'd get light over the whole sensor - however, the flash duration is only half the story - the power of the flash changes over the flash duration. So, the lighting would still vary across the sensor.

Fourthly, the shutter speed is about capturing the image in ambient light. If the ambient light is too low, any motion will effectively be frozen by the flash duration. This would then come down to the individual flash unit.

Fifthly, what shutter speed you can set would be dependant on the camera knowing if there is a flash attached, and what it does about it.

so, in answer to your question:


When in manual everything mode and using a radio trigger of some sort, can you manually set up the exposure with a shutter speed higher than the stated max flash sync and still have your flash light your subject without any part of the shutter curtain showing up in the frame?


I think the answer is yes, you can set a higher speed and no, you can't reliably stop the shutter curtain showing.

As to your scenarios, in eg1, if you need a higher shutter speed than sync for ambient exposure, you'd need to either stop it down or use an ND filter to get to a speed lower than sync. In eg2, you'd have to rely on the flash duration - how you'd vary that I am not sure, but power levels could be one way given the way flash circuitry works.

[swifty]

Thanks everyone for ur insights.
Rob: thanks particularly for ur points, esp point 3. about power of the flash varying over the flash duration. I thnk Andrew mentioned this sine wave phenomena before but it didn't click with me.
So in conclusion, for me anyways the flash sync limitation of m43 without FP mode would mainly be for on-the-go on-camera balance fill flash with large apertures in bright lighting conditions.
For set up shots ambient can largely be controlled by use of ND filters although at the expensive of ur strobe output and if ur subject is lit by the strobe which have pretty short durations then freezing subject motion ain't a big prob.
Cheers everyone.

[I @ M]

Picture examples from a quick muck around today.

SB800 sitting on a stand and running at varying outputs to give somewhere near consistent light levels.

D700 with inbuilt flash manual mode at minimum power optically ( SU4 mode ) triggering the SB800 at 1/320 which is the maximum synch speed you can set the shutter to.
http://a03-b03.mypicturetown.com:80/P2PwebCmdController/cache/HPtAFfP9pbdSCyv*X1J45UnPpw6l44OQxazqGz%26XA4j2*_7%3DsHFDsQX4.*-14a%3Do/item.JPG?rot=1

D700 with yong nuo radio trigger firing the SB800 at 1/320 which is the maximum synch speed you can set the shutter to as the camera detects the radio trigger as a flash ( I think ).
http://a03-b03.mypicturetown.com:80/P2PwebCmdController/cache/4zoFEUV%26.6YZ1O7F-jjJz%26-Es%26S8A*FGKuRo7_OH8D%26-QRPvq*.J%3DHiJa1APqr.4/item.JPG?rot=1

D50 with yong nuo radio trigger firing the SB800 at 1/800. The rated maximum synch speed of the D50 is 1/500 so I assume that the D50 doesn't know that a flash or trigger is attached.
http://a03-b03.mypicturetown.com:80/P2PwebCmdController/cache/pbR0mdm*iaPdFFE*rfUU.*CaZCgTPJDJITiDIfAWbX8*bHM%25JZ7p2GBcA1k2v%256I/item.JPG?rot=1