Some time ago, I was playing around with my DsMk2 and the Speedlite 580EXII in manual, shooting RAW, when I got four really strange exposures; it seemed that a section of the sensor simply didn't record the incoming light. Below is an example, shot at 1/500 at 3.5.

The problem vanished after my turning the camera and flash off and on, not to be seen again since. Anyone got ideas about what could have caused this?

Cheers,
Paul



Edited by Paul Walden on Aug 07, 2008 at 12:00 AM GMT

EXIF data would be helpful, but it looks like your shutter speed was faster than the max sync speed.

Hi Rob!

Of course, sorry, thought I'd ticked the EXIF box. The shot was taken at 3.5 1/500, and I'm pretty sure the flash was in high-speed sync mode. Strangely, though, the EXIF says that the flash didn't fire at all.

According to the MkII manual, the camera should be able to sync up to 1/8000, and the 580EXII manual claims that the flash can sync with any shutter speed. So I'm still at a loss as to what caused this odd exposure. Am I misreading the manuals?

Rob Whiting wrote:
EXIF data would be helpful, but it looks like your shutter speed was faster than the max sync speed.

+1

Actually, now that I double-checked it, the EXIF data of other pics, where I know that the flash DID fire, say that the flash didn't fire. What am I missing here?



Edited by Paul Walden on Aug 07, 2008 at 12:01 AM GMT

My guess is the flash was not fully seated. The main contact on the shoe is large, so it was making contact, but the other 4 contacts were not. As a result, the flash fired as it was told, but without guidance on how bright to fire. It did not know it was on a camera, so it did not go into high speed sync mode, which explains the 1/500s shutter with the shadow from your curtain.

Ben, thanks for that! I guess I simply hadn't pushed the little lock-in lever on the flash mount across. And, of course, it's the shadow of the curtain that we see. Feeling slightly embarrassed that I didn't realise that at first.

Cheers!
Paul

If your EXIF says flash did not fire, then my guess is that your body lost communication with the flash for a few frames. As long as the center pin of the hot shoe has a good connection, it will still trigger the flash to fire. But if the other pins are not (well) connected, the camera will not register the flash and be able to communicate with it.

This could also be causing the flash to revert back to non-HSS mode (it has no information which shutter speed is selected and hence does not know how long to stretch the flash pulse) which then caused you to see the second curtain at the edge of your pictures as your shutter speed was beyond the mechanical sync limit of the body.

Just a guess...

EDIT: Ben beat me to it

it's time to make sure that the hot shoe on your camera is tight. If it is a bit loose then you'll get this sort of strange behaviour even before it feels loose.

- Alan