7D Internal Flash (sync?) Problem HELP.

[creepyNick]

I recently got my 7D back after it was being fixed for a broken cf pin.

The problem now lies with the flash, the flash DOES pop and it does fire, but there's no flash effect on the photo sometimes. Heres 2 photos, same settings but 1 is iso 1600 and the second is iso 2000.




Both photos the flash did pop and did fire.

[RobertTheFat]

Canon flashes using ETTL are extremely averse to overexposure and always favor the highlights. Which means that you normally have to expose for the scene and treat the flash as fill. Whether the difference in the ISO settings fully accounts for the difference in brightness is hard to say. One other possibility, I suppose, is that the ISO 2000 image (which, from its number, is the earlier one) was taken before the flash's capacitors had time to reach full power.

[Skirball]

The flash didn't fire in that second shot; there's no specular highlight (from the flash) on the blue trashcan lid in the second shot.  You can see it clearly in the first.  All the shadows also indicate an overhead light source is dominant.  Unless you were using a really long lens even a low powered flash would have done something.  Is it possible that you managed to completely cover the flash with a hand or arm or something?  It's hard to cover it completely, but it's possible. 

I wonder if it was only a preflash, though I'd think the EXIF wouldn't report that the flash fired in that case.  It's possible, I suppose, that it fired at the lowest power level, but at ISO 2000 and f/5.6 I'd think you'd see at least something from it.

[creepyNick]

This is the problem, i can provide a few other examples where the flash did fire (Not only pre fire) and XIF data shows that the flash fired as proof, but isn't showing in the image. The flash was not covered.

Obviously i'm speculating but it is almost as if the flash fires too early or late so that it is not captured in the image? I can't think of why this happens, I never had this problem before the cf card reader replacment. 

[RobertTheFat]

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@creepyNick wrote:

This is the problem, i can provide a few other examples where the flash did fire (Not only pre fire) and XIF data shows that the flash fired as proof, but isn't showing in the image. The flash was not covered.

Obviously i'm speculating but it is almost as if the flash fires too early or late so that it is not captured in the image? I can't think of why this happens, I never had this problem before the cf card reader replacment. 

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Firing too late is hard to envision, but firing too early (or appearing to) could result from a sticky first shutter curtain. Possibly the mechanism got damaged when they dismantled the camera to get at the CF socket.

If the problem is that closely tied to the repair, I'd be inclined to send the camera back to the shop. Even if the problem appeared to go away, how could you be sure, given that it's sporadic anyway?

Can you reproduce the problem with an external speedlight instead of the internal flash? If not, it suggests that the problem may be electrical rather than mechanical.

I assume that you've ruled out sluggishness in the pop-up mechanism. That should affect only the first shot in a sequence, since I believe the flash will stay up until it's pushed back down.

[creepyNick]

I don't want to say that the flash IS firing too early, because it's to hard to tell. All i meant was thats what it looks like on the final image, that the flash isn't even there, when i know that it did indeed fire.

Unfortunately i dont have access to a speedlight or flash. And yes the images shown above were taken seconds apart with the flash already popped up.

It's a really odd problem that I haven't seen anyone else complain about online. I'm not sire whats causing it, or how to fix it. Any help is appreciated.