50D Flash Sync problem

I sense a few people may have had experience with this problem, so here it goes:

I just bought a used 50D, and I've discovered that if I use the flash (either onboard or external , my 430EX), the first shot is always exposed properly, but the 2nd shot is exposed as if the flash sync speed is off (thick black banding on the upper half of the image, properly exposed sliver on the bottom). I have been able to reliably reproduce the problem so long as I take 2 pictures with the flash; the 2nd one will always be banded.

I found that this problem happens no matter what mode I'm in (M, Av, Tv, P, Auto) and no matter what shutter speed I use (anything from 1/8000 to 1/10 is what I've tried); as long as I'm using any flash, the image is always banded on the 2nd shot and every shot with the flash thereafter until I shut the camera off and turn it back on.

This seems more like a communication problem than a shutter problem, and I wasn't able to cause any banding by shooting without a flash at high shutter speeds alone. I tried updating the firmware to 1.07, but doing so didn't fix the problem. The camera exposes fine all the time without the flash (so far).

Is this camera hooped, and am I hooped on the warranty for buying a 2nd hand camera?

Can you post an image shot with the flash set to High Speed Sync (HSS) and a shutter-speed above 1/250s that shows the problem?

I wonder if the flash isn't set to the HSS option that allows you to go above the fixed camera flash sync speed which would cause the dark line on images with that setting off.

I just took some pictures, and discovered I was wrong with my observations; the banding only seems to occur when my shutter speed is slower than 1/250 and HSS on my 430EX is off. The problem seems to vanish if I faster than that and HSS is back on. Note that this problem exists with either the 430EX or the onboard flash.

Here are the images:

1/60, Camera power cycled, 3 consecutive shots, no change in settings:

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What size Ah batteries are you using. Are you using the flash on full power. Depending on these settings it will have an effect on how fast your flash is recycling, thus the flash is not keeping up with your shutter causing the bands

The higher Ah batteries (eg 2700mAh) and the lower power rating on your flash (eg 1/64 or 1/32 power) the faster the recycle time.

Yep:

your 50D flash synch speed works at either : 1/200sec 1/250sec 1/300sec.

Set a TV of 1/500sec (without HSS) and you will see this black banding
Set a TV less than your flash-synch speed and you will get the subject exposed correctly with some ambient exposure.

To use your camera and flash effectively at speeds above the "flash-synch-speed" you need to activate HSS on your flashgun. This will allow you to set a TV of anywhere from 1/250sec all the wayy to your maximum shutter speed of 1/8000sec. When you do this, only a tiny amount of light is emitted by the flashgun and you are able to take consecutive shots because the flashgun still has retained battery-power charged for the next shot.

Have you given the flash enough time to recycle between shots?

Looking at the first series, there is no flash highlight in the 2nd and 3rd image. Suggests to me that the flash is not firing at all after the 1st shot, or that the area where the highlifght would be is obscured by the second blind when it finally does fire (which I guess actually explains why there is a lighter band at the bottom of the frame).

Also, I don't understand how shutter speeds above a 1/250th will work effectively with flash.

My understanding is that when using flash, the shutter must be fully open when it fires. Otherwise part of the frame is obscured by one of the shutter blinds.

With a focal plane shutter, this only happens when the first blind has reached the bottom of the frame and the second blind has yet to be released. On the 50D, the fastest shutter speed where this happens is a 1/250th. Below a 1/250th this is what happens every time. Faster than this and the second blind is released before the first blind has reached the bottom of the frame, that's how the shorter exposure is achieved. The physical speed of the shutter blinds is unchanged irrespective of the shutter setting. I remember a 1/125th flash synch being a breakthrough. For years, the shortest exposure or fastest synch speed for a focal plane shutter was a 1/60th and my old Zenit E with a horizontal cloth shutter was only a 1/30th.

To be able to help you, please make sure about these things:

Turn off High Speed Sync, if it's enabled (external flash only).
Set camera to Tv, turn on flash, wait until the flash charge symbol in the viewfinder is on, then first half-press the trigger, let go of the button and before the viewfinder information turns off, verify that you can't set a shorter time than 1/250 s. If you can, there's something wrong with the communication between flash and camera.

Now use a shutter speed of 1/250 s, nothing else.

Take your three pictures, but make sure the flash ready icon is visible in the viewfinder between every shot!

What happens?

Maybe also not shoot in a room with tube lighting.

apersson850 wrote in post #10582130
To be able to help you, please make sure about these things:

Turn off High Speed Sync, if it's enabled (external flash only).
Set camera to Tv, turn on flash, wait until the flash charge symbol in the viewfinder is on, then first half-press the trigger, let go of the button and before the viewfinder information turns off, verify that you can't set a shorter time than 1/250 s. If you can, there's something wrong with the communication between flash and camera.

Now use a shutter speed of 1/250 s, nothing else.

Take your three pictures, but make sure the flash ready icon is visible in the viewfinder between every shot!

What happens?

Before I go on, I would just like to update that today, I can't recreate the problem that I was showing yesterday; using the exact same settings (1/250, f/4, ISO1600, no HSS), every 2nd or 3rd shot is now entirely dark, as if the flash did not fire. I am unable to reproduce such a problem on my 40D. I think it's safe to say that something has changed today but a problem still exists.

On Tv, the camera won't allow me to set a shutter speed shorter than 1/250s with HSS off (there does not seem to be a problem with communication between the camera and flash). Using a shutter speed of 1/250 s and taking 3 shots, the camera exposes properly for 2 shots, but is dark by the 3rd shot without a black band, as if the flash did not fire. This then seems to occur at shutter speeds slower than 1/250 (I tried 1/100 and 1/60), but not at any shutter speed faster (I tried 1/320 and 1/500).

At this point, the camera does this at every setting with shutter speeds slower than 1/250, and not with shutter speeds faster than 1/250. The camera will properly expose the first shot, and intermittently underexpose subsequent shots. This occurs with both the on-board flash and the 430EX, as long as I am shooting slower than 1/250. Doing the exact same test with my 40D, I am unable to recreate such a problem; the camera exposes properly with the flash at all times regardless of shutter speed.

As I said previously, I can't recreate any banding like I could yesterday, which again leads me to suspect something is wrong.

CyberPet wrote in post #10582768
Maybe also not shoot in a room with tube lighting.

I don't understand how this is relevant?

bokchoi wrote in post #10582840
Before I go on, I would just like to update that today, I can't recreate the problem that I was showing yesterday; using the exact same settings (1/250, f/4, ISO1600, no HSS), every 2nd or 3rd shot is now entirely dark, as if the flash did not fire. I am unable to reproduce such a problem on my 40D. I think it's safe to say that something has changed today but a problem still exists.

On Tv, the camera won't allow me to set a shutter speed shorter than 1/250s with HSS off (there does not seem to be a problem with communication between the camera and flash). Using a shutter speed of 1/250 s and taking 3 shots, the camera exposes properly for 2 shots, but is dark by the 3rd shot without a black band, as if the flash did not fire. This then seems to occur at shutter speeds slower than 1/250 (I tried 1/100 and 1/60), but not at any shutter speed faster (I tried 1/320 and 1/500).

At this point, the camera does this at every setting with shutter speeds slower than 1/250, and not with shutter speeds faster than 1/250. The camera will properly expose the first shot, and intermittently underexpose subsequent shots. This occurs with both the on-board flash and the 430EX, as long as I am shooting slower than 1/250. Doing the exact same test with my 40D, I am unable to recreate such a problem; the camera exposes properly with the flash at all times regardless of shutter speed.

As I said previously, I can't recreate any banding like I could yesterday, which again leads me to suspect something is wrong.

Have you tried resetting the custom functions for flash control?

These are on the 3rd system tools menu (7th from the left), under flash control.

By default the camera will synch the flash to the first curtain. You could try synching flash to the second curtain (same menu). For a static subject this should make no difference, but if it improves your problem, then maybe the issue is to do with the first curtain.

Geejay wrote in post #10583610
I don't understand how this is relevant?

The pulsing of fluorescent tubes can cause some color banding and exposure inconsistencies in some cases. Not the problem here though.

gonzogolf wrote in post #10583709
The pulsing of fluorescent tubes can cause some color banding and exposure inconsistencies in some cases. Not the problem here though.

Thanks...