Paul C. Buff, Inc. Technical Forum

Hi, I use the Einstein 640 along with my Canon 5DMarkII (5DM2 in short).

The thing about 5DM2 is that I can't open up the flash settings in the menu if no flash is mounted on it. At least that was how I set my flash to rear curtain sync when I had my Canon Speedlite mounted on it.

Does anyone know how I can set rear curtain sync with Einstein 640 and Canon 5DM2? I have a CST mounted on my 5DM2, a Cyber Commander at hand, and a CSXCV on my Einstein.

Mucho gracias!

Canon cameras do not support 2nd curtain sync with a non dedicated hotshoe device (a flash or remote).

Have you tried mounting your flash on the 5D, setting it to second curtain sync and setting the power as low as you can on the mounted flash and using the optical trigger on the Einstein? My Speedlights fire my Einstein just fine at minimum power. Probably won't work if any distance is involved or out in the daylight...

James

This should work, however, remember to set your speedlite to M, otherwise it will trigger the lights too early due to the preflash.

Anyone know any similar discrepancies using Nikons, as it might be helpful to others?

I'm usually in rear-curtain (using CST at anywhere from 250th-60th), but I've noticed the few times I've shot in front curtain that my exposure comes in about 1/3rd of a stop brighter than in rear under the same settings for any given shot, but it's doesn't seem to be the curtain shadow effect (black bands over max sync), it's across the whole frame. I've run these tests on Manual using 250th, 200th, 125th, 60th, 30th shutter speeds = same 1/3rd or so stop difference across the board. Not enough to get fussy about and doesn't affect my shots (since it afffects entire frame), but just putting it out there in case anyone has a similar experience - or better yet, an answer why it might be happening? (most likely user error! :P )

Haven't tried using a hardwired sync cord, maybe it's the delay from the CST/CC, but even at 125th & 60th, seems doubtful...

In rear curtain sync, your shutter speed (assuming no ambient at all) will not affect the lowered exposure. (it could affect it in first curtain, however, given a long enough flash duration). This is due to the flash being fired just before the curtain closes. The time before the curtain starts to close is irrelevant.

Depending on your flash unit and power settings and camera, this is not particularly surprising. I would exect some gradation on fast flash durations, while slower durations would appear more even. Again, this would depend on the camera, in particular, how fast the shutter blades move.

The reason behind this is that the flash fires just before the shutter blades start to close. The flash is (well,...can be) still burning as the sensor is getting covered. Because not all of the flash output is reaching the sensor, the exposure is lower. This is similar to HyperSync (and similar technology), but in reverse. This is also why a camera may state 1/200 of a second sync speed with speedlites, but lower sync speed with studio lights, even in first curtain (flash duration is longer than shutter operation).