Toronto Photography Meetup Group

Hi there,

I'm using strobes and the bottom half of my photos are black when my shutter speed is faster than 320.

I'd like to use a faster shutter speed to capture motion more clearly, but faster shutter doesn't seem to be letting enough light in.

Is there any way to avoid this black bottom while using a faster shutter speed?

Thanks!

Krista

Your flash sync speed on your camera is only 1/320 of a second going faster will not sync with your flash Ie that black strip is your shutter showing up in your picture You need a strobe with a high flash duration (to freeze motion)

What are you trying to freeze motion of?

Flash sync speed on the 50D is 1/250 sec - if you go any faster than that you are very likely to see the shutter intruding in your shot. But what's important is the duration of the flash output. Putting ambient contamination aside for a second, if your flash output duration is 1/1000 sec then as long as your subject is not moving incredibly fast - like dancing, running, etc you should be fine in freezing the subject with a camera shutter speed of 1/250 sec since the flash is the only light illuminating the subject, thus freezing motion at 1/1000 sec.

Here's a quick link to flash duration of the 580ex and freezing motion.

http://www.photosbykev.com/wordpress/20 ... -duration/

by any chance, is there a link for the 430ex

http://www.waynesthisandthat.com/flashdurations.html James you beat me to it lol

Not sure where to find it in canon land, but a quick google shows the 50D does support "High Speed Sync". On Nikon this is Auto-FP buried in a menu... this will allow you to sync faster than your camera's standard sync rate and remove the curtain from the image.

On the 5D Mk2 I find the high speed sync is 1/200 sec but I can achieve 1/250 sec only when attached to the strobe with a cord.

yes, but only if you use Canon/Nikon branded flashes. If external studio strobes or non-branded flashes which do not talk HSS are used and/or if the flashes are synced via dumb connections, HSS will not work.

Aha, good to know!

Yes, 5D, 5D mkII have "rated" flash sync speeds of 1/200 - the 7D, 50D, 40D, etc have "rated" flash sync speeds of 1/250 - but as you say they can be pushed a little with corded operation. This is not to be confused with High Speed Sync which is a different thing altogether

Some more information here:

http://www.rpphoto.com/howto/view.asp?articleID=1026

The other option is to find a Nikon D70 or D40 DSLR or a camera with a leaf shutter.

g10 would be nice

"Sync speed" is the fastest shutter speed that the ALL of the shutter is fully exposed to light at the same time...any faster, and the rear (2nd) curtain starts closing before the front (1st) curtain is fully open.

You get the black because the strobe is just a short burst of light, and only the part of the shutter that is exposed to light at the time the strobe fires, "sees" the flash lit scene...the rest sees only ambient light.

Typically flash is fast enough for capturing high-speed action, even someone jumping in the air or freezing water motion:


Now if you were using TTL compatible flashes, you could use HSS(High Speed Sync)/FP(Focal Plane) mode on your flash to gain higher shutter speeds, but you lose flash output by 1/3 to 1/4 because instead of a short burst the flash outputs a longer burst or a series of bursts.

I don't know if you mean with studio strobes, but there's a workaround floating around for working with studio strobes faster than your sync speed. I can't remember where I saw it right now, but you basically set your strobe on optical slave, put a hotshoe flash on your camera and put it in high speed sync mode, manual power level to the lowest possible so it doesn't contribute to your exposure. Somehow by putting it on high speed sync it triggers the strobe at the right timing to light your entire frame. I think the trick works because strobes control the amount of light by lengthening or shortening the flash duration, so for example if your strobe dumps out a flash for 1/1000s on a certain power level you can sync at 1/1000s or faster because the strobe will be on for at least the duration of your exposure and you won't get a black band. You'd have to experiment to see what your particular combination does.. I think one person even taped an optical slave in front of the hotshoe flash which was connected to a Pocket Wizard so that they wouldn't have to rely on the studio strobe's optical triggers if using this outdoors.

I found the link:
http://www.flickr.com/groups/strobist/d ... 724354633/

As you can see, they were able to get to 1/8000sec!

Hmm, perhaps I should post that link somewhere else on TPMG, is there a better subsection?

Pretty cool hack. I'll have to give that a try... Thanks.

Having a background in electronics, there's something not right with the "hack".

Basic strobes only respond to one "command", and that's "fire"...it doesn't matter if it's "said" slowly, or "said" quickly...the "dumb" strobe itself won't change the rate at which it fires; unlike a TTL flash which changes settings depending on how you set the camera.

Reading further they talk about this only working when the other light is at 1/1 ratio which explains a few things...in order to vary the light output, flashes vary the duration they are on, rather than the intensity of the light. At higher output the flash duration is longer and therefore should cover the frame...albeit not uniformly, as this person's white wall experiment shows.

Yes you would need an HSS/FP flash to trigger your slaves as they have to be triggered before the 2nd curtain starts closing, rather than x-sync which is when the first curtain is fully open. Also you have to set your HSS/FP flash to a manual power level that won't interfere with the strobe lighting, and so a preflash isn't emanated from your TTL flash (which would fire your slaves early and so they will be dark when the actual picture is taken).

This will all depend on what strobes you use as they have various durations depending on design, and how much power they are.

Your exposure values will vary!

I don't think they claimed the strobe would know how to change the way it fires, the point was that because you're on HSS the timing of the first flash would coincide better with, as you later mention, when the 2nd curtain starts closing such that a strobe with a long enough flash duration would light the entire frame.



I think this is a given; this is a workaround so there are going to be issues because the equipment wasn't meant to be used in this way. The point was that you could sync up to 1/8000s which in and of itself has merit. Anyways I don't have the technical background that you do so I don't understand all the technical issues at play, but I think the fact that it even works at this speed is pretty cool.

Oh yeah, you're right as I mentioned in my post above as long as the flash duration is longer than the exposure it will cover the whole frame which is one of the ingredients for why this hack will work..

another point to remember is that the lower the output of your strobes the shorter the duration of the flash. So if you really need to stop more motion or something and can get away with a wider F-stop you could try that as well.

For the most part 1/250 is plenty fast for most needs, like fashion or such.

I think their ultimate application was to overpower the sun while keeping a wide aperture for shallow DOF.