Flash Sync Speed Issues

[madFive]

I experienced a really weird issue the other day when shooting with my remote flash setup. Wondering if you guys might have any solutions for this.

On my D90 the max flash sync speed is supposed to be 1/200”. I have successfully gotten images to turn out as high as 1/250” by attaching my SB900 by pc-cable to the hot-shoe, which unlocks the shutter speed. By using that method, anything much over 1/250” causes some weird black bars to appear in the photo: something to do with the movement of the shutter leafs and the way the light from flash falls across the subject.

A few days ago I decided to take some product-shots with my new macro-light-box (large cardboard box w/ holes cut in it, holes covered w/ white shower curtain or tracing paper, and lots of duct-tape). I set up two flashes (SB900 & SB600) on stands on either side of the box, each hooked to a pocket wizard, and a third PW on my camera to trigger flashes.

I started with the flashes set to about 1/8 power and the camera shutter at a modest 1/180”. But to my shock and horror, about one out of every two or three shots was having those black bars, like I was exceeding the acceptable sync speed! I tried turning down the shutter speed as low as 1/100”, and also checked my camera’s flash-settings to make sure I wasn’t using rear-sync or any other unusual settings (guessing I missed something); but randomly one out of every few shots was still getting the black-bars error.

After this, I also tried shooting some with just ambient light to make sure something wasn’t just completely messed up with my shutter. With ambient light, out of a couple dozen shots, none of them had the black bars; so I don’t think the shutter is doing this on a regular basis – just something wrong in my flash setup.


Cliffs: When using remote-flashes and pocket-wizards, my camera-shutter speed is refusing to sync properly, even at speeds as slow as 1/100”. It happens intermittently, not in every shot.

Any idea what could cause this? Is there something wrong with my camera’s shutter? A setting on the flashes or PW’s that needs to change? Any help would be appreciated – I would hate to have a really important shot ruined at some point because of a sync error.

 

[northrop]

does it happen when u use the sb900 only? have u tested ur setup using the sb600 by itself? i dont use strobes that much but it seems ur sb900 is causing the problem. care to post a sample?
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[madFive]

eh... just picture one of those gun photo's in the "picture I took" thread, only the bottom third of it is completely black. I deleted all of these mis-fires in-camera as they happened, so there's really nothing to post at this point.

Yeah - this issue needs a lot more trouble-shooting. I was using both the SB900 and SB600 at the same time, both aimed in oposit directions. You'd think if just one of them was having a problem, then the dark stripe in the photo would still be half-way lit (that might actually be really cool looking ...hmm). But when I got the problem, it was a completely black stripe across the bottom of the image.

Since this problem was only happening on like every other shot, I just kept shooting and eventually got what I needed. Seemed really bizzare that it happened so inconsistantly. Now that I'm thinking about it, one very likely explaination would be a loose conection in the cables somewhere; and would probably have had to be between the camera and first PW, since both flashed were eventually firing for each shot. Next time I shoot with this setup, that'll have to be the first thing I check: conection between camera hot-shoe, cable, and PW...

 

[northrop]

recycle times are different for SB900 and SB600. with that in mind, is it possible that one of the strobes is setup too low/too far, and thus the bottom portion of your box is blocking about 1/3 of the light source from one of your strobes entering your soft box? with mixed up recycle times, perhaps one of the strobes wasn't firing, or was firing with not adequate enough power to light up the subject properly? this is all very hypothetical, but this is the best i can think of right now.

 

[madFive]

I tried again last night, this time checking to make sure everything was connected and seated properly; replaced all batteries, and placed light stands a little farther appart to hopefully avoid any radio interference between the units.

This time I got the expected results. Sync was fine up to 1/200 and started to show a little banding at 1/250. Still not sure what went wrong last time (at 1/100 I was getting banding that covered 30+% of several shots) but it looks like, with a little more carefull setup, I can avoid the problem in the future.

Here's a few example shots, in case anyone wants to see what a sync error on D90 looks like.

D90, 50mm f/1.4 AFS @ F/8, SB900 and SB600 on sides, shutters @ 1/200 and 1/250

 

[northrop]

glad u got it sorted out. pics look great!
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[Tim_axe]

What direction does the shutter travel on the D90? Isn't it top to bottom? Remember that the image on the sensor is inverted so the bottom left of your photo is from the top right of the sensor when you look into the body after removing the lens.

Which means that you're having some kind of issue with syncing and the rear curtain - is your flash settings set for front or rear curtain sync? I'd check that.

On the rear curtain sync if you have any lag/delay (maybe the PW has some lag) you'd probably end up getting what you are seeing. I've always had my flash on the hot-shoe, never used a PW or similar wireless flash trigger/control so I don't have experience with this particular flash sync error (but I did have the AF mirror fail on my digital rebel once - that is a black bar at the top of each photo since the AF mirror covered the bottom of the sensor). But it seems to explain what you're seeing.

 

[madFive]

^^^ Thanks for the info. I'm still pretty hazy as to how the shutter and AF mirror etc works in my camera or any others. So you're saying my flashes are firing too late, or too early? I assumed they were firing too late, as it just seems really unlikely that anything could cause them to fire too early.

When I first started noticing this issue, I made sure the sync was set to front, not rear curtain, but that didn't really seem to help.

The problem happens completely intermittently, maybe one out of every 5 shots or so, regardless of the shutter speed; so it really seems like something in the wiring is loose, not a problem with the shutter itself; and since when the error occurs, it affects both flashes equally, my conclusion was that it is a problem between the camera and the first PW unit...

I still have some more trouble-shooting to do - haven't really looked at any of it since last weekend, but I'm hoping that replacing that one adapter, and being more careful when setting up all my lights and wiring should keep the error from occurring again.

 

[PS-RagE]

Why use Pocket Wizards at all? The CLS is awesome. Anyhow, slow down your shutter speed to 1/60 and you should be fine. No point in making those flash guns pop so hard

 

[madFive]

^^^ I've been using the CLS system for a little while, and was running into its limitations fairly often. The range is fairly limited; camera has to be in direct line of sight, so certain angles don't work; I've been in a few situations where IR interference or bright sunlight kept it from working etc; but mostly I didn't like how I had to dig through all the menu's to get it set up and working properly every time I wanted to use CLS - too much room for error.

I haven't tried slowing the shutter down that much yet, but it's definitely worth trying. Seems like at anything under 1/4 power, the speed of the flash is a lot higher than even the top shutter speed on the camera, so the shutter speed is really irrelevant when doing this. A higher shutter speed should just keep the ambients in the frame from getting any motion blur.