Help! Black streaks across photos

So I was taking group pictures for this banquet, and all was going well until my camera started giving me these weird black bands across the bottom of my photos. It started out more like extreme vignetting on just the bottom, but it got worse as time progressed.

I was using an old speedlite 155A from my AE-1 film camera attached to my 30D and I had a Sigma Super in slave mode through an umbrella on the right side. I turned it off by the time I was getting to these photos because I was afraid it was overheating (other people's point & shoots were setting it off full power). Attached are some of the worst pictures. By the 2nd picture, I was already trying to compensate for the black band. When I opened the RAW files in Photoshop and turned up the exposure, it started showing the image under the black band. These were taken on a 30D with the kit lens. Same thing happened with a 28-105mm, but then after about 10 minutes, it was taking pictures fine. I was using a Sandisk Extreme IV 2GB.

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Shutter may on the way out

It's not the shutter. It's your shutter speed. 1/500 is not possible with this camera and these flashes. yuor sync speed is going to be about 1/200 to be safe.

yeah, i didnt think it was the shutter because I just bought it back in January. I thought it could have been something with the mirror, but the shutter speed makes sense also. Thanks Cosworth

cosworth wrote in post #3322175
It's not the shutter. It's your shutter speed. 1/500 is not possible with this camera and these flashes. yuor sync speed is going to be about 1/200 to be safe.

Cosworth is absolutely right. This is a classic case of synch speed mismatch.

Mark

Strobes only sync up to a certain speed with the camera. Some only sync at 1/60th or slower. But try 1/200th or slower.

A focal plane shutter (the type in all DSLR cameras) is made up of two curtains. When the shutter is fired, the first curtain opens followed by the second curtain to close the shutter. When flash is used and the shutter speed is too high, the second curtain has already started to close when the flash fires, hence the black bar in the image. This is why cameras have a maximum sync speed for electronic flash.

Early SLR film cameras had cloth shutter curtains that traveled across the film plane. Now the shutters are composed of metal blades that travel vertically, usually from bottom to top.

good to know. Thanks.

How then does high-speed sync on flashes work?

ooops

HSS fires multiple pulses of light extremely quickly and repeatedly to cover the entire frame. So one burst as the shutter is open for the top part, and another burst to light the bottom of the frame (what you are seeing as the black, unlit area in your exposures) as the shutter moves. Rinse, repeat

HSS/FP flash typically requires dedicated flash units, though.