Flash Sync question

[Scott Knowles]

Ok, it's a basic, and somewhat dumb question, but I'll ask anyway. And my learning technique is to push something until I don't know and then research and ask. Ok, the question.

Due to the cold winter weather, and getting older, I've moved my work indoors. I started using the 4x5 camera to trigger the Pocket Wizards to the flashes. All my lenses are newer Schneider lenses. I've read different explanations of the shutter speed for x-sync, from 1/125th and slower (Jim Stone's book) to any speed (Leslie Stroebel's book), the latter because it triggers when the shutter is fully open and any shutter speed is slower than the flash.

So far I've been using 1/60th for the aperture (f11-22), but I am curious if I could use any shutter speed. Any ideas or answers beside the obvious test it?

The one thing I have learned is that I have to isolate the PW in the coldshoe because it shorts the signal because PW's have single contact for camera hotshoes. Using a standard off-camera hot shoe work to isolate the PW from the camera works for the x-sync camera to PW cable.

[Ralph Barker]

Properly-working leaf shutters will x-sync electronic flash at any speed on the shutter. (That's one of he advantages, for example, of the leaf shutters in Hasselblad lenses.) You might still want to use a slower shutter speed, however, if you want to increase the amount of ambient light contributing to the total exposure (e.g. an interior scene where you want ambient lights to show), or if using a strobe that has an unusually long flash pulse duration. (Some older flash units have a pulse duration of around 1/300 sec, while most newer ones are around 1/1000 or shorter.)

Naturally, you can test by taking a series of exposures at each of the marked shutter speeds and the same f-stop with all of the ambient lights turned off.

[Scott Knowles]

...Naturally, you can test by taking a series of exposures at each of the marked shutter speeds and the same f-stop with all of the ambient lights turned off.

Thanks for the response. I'm using 3-4 Minolta 360PX's in two small softboxes and a Canon 580EX in one large softbox with little or no ambient light. I use a pair of Lowell Tota lights for preparation and some b&w. The studio is a temporarily converted dining room (photo below).

Question about the tests, why keep the aperture the same through the range of shutter speeds? Wouldn't it just be a progressively darker image? To test the consistency of the exposure, wouldn't you adjust the aperture accordingly? Or, as usual, I'm missing something?

[Nick_3536]

With in reason shutter speed has zero effect. Until you get so fast the shutter is faster then your flash. Or you get so slow the ambient light starts to add to the total exposure.

So keeping the F/stop steady and just changing the shutter speed won't matter.

[Bob Salomon]

Thanks for the response. I'm using 3-4 Minolta 360PX's in two small softboxes and a Canon 580EX in one large softbox with little or no ambient light. I use a pair of Lowell Tota lights for preparation and some b&w. The studio is a temporarily converted dining room (photo below).

Question about the tests, why keep the aperture the same through the range of shutter speeds? Wouldn't it just be a progressively darker image? To test the consistency of the exposure, wouldn't you adjust the aperture accordingly? Or, as usual, I'm missing something?

The aperture required is determined by the output of your flash and the flash to subject distance. The shutter speed is used to balance the flash exposure to the ambient light. By changing the shutter speed you could have anything from a totally dark background at the shortest shutter speed to equal brightness to a background that is much lighter then the flash exposed subject. That is the advantage to a leaf shutter with EF.

[Gordon Moat]

Generally, the strobes control the exposure, in combination with your aperture setting. However, if you leave the shutter open longer, then you also add more of the ambient light in the room. So you could put the shutter at one second, have the strobe control the majority of the exposure, then the shutter allows ambient light to continue exposing the film after the strobe has fired.

I have also seen this used to great effect on several minute exposures. Perfect example is capturing a person in a scene, then leaving the shutter open. The person could actually walk out of the scene, while whatever ambient light continues the exposure.

I also switched to a mostly multiple Nikon Speedlight set-up not long ago. I find the small battery powered strobes easy to carry, set-up, and control. The other benefit is not needing any plug-in power source.

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[Scott Knowles]

With in reason shutter speed has zero effect. Until you get so fast the shutter is faster then your flash. Or you get so slow the ambient light starts to add to the total exposure.

So keeping the F/stop steady and just changing the shutter speed won't matter.

The flash of insight. Now I see. Thanks. Sometimes these "Duh" moments just take awhile.

[Ralph Barker]

Yes, the intent of my suggested method was to make sure the sync was working properly at all shutter speeds. Keeping the f-stop static (with all ambient lights off) should result in consistent exposure on all of the images.

[Scott Knowles]

Yes, the intent of my suggested method was to make sure the sync was working properly at all shutter speeds. Keeping the f-stop static (with all ambient lights off) should result in consistent exposure on all of the images.

And as I learn, you are so right. I set up the Canon 5D with three softboxes on one small subject, flash metered the subject to f8, started at 1/200 and went through every shutter speed to 1 second, and nary a difference in the images.

Thanks for the help.

[Ralph Barker]

Your test with the digital confirms the concept. If you are unsure about the operation of the shutter on the LF lens (e.g. if it's an old one), you may also want to do test exposures with your LF camera using the lens in question. If the shutter blades are sluggish at one or more speeds, for example, you might see a difference in exposure at that/those speed(s) due to the blades partially obscuring the light path. You might even see something resembling the starfish pattern the shutter blades form when they are partially open. The flash isn't supposed to be triggered until the shutter if fully open, but sometimes Murphy's Dust creeps into old shutters. ;)

[steve simmons]

And as I learn, you are so right. I set up the Canon 5D with three softboxes on one small subject, flash metered the subject to f8, started at 1/200 and went through every shutter speed to 1 second, and nary a difference in the images.

If there was any significant ambient light in the space there would have been a difference. When I was an architectural photographer and used strobe for my interiors I used the shutter speed to control light coming in from the windows.


steve simmons