Paul C. Buff, Inc. Technical Forum

I've made the combination of a Hasselblad H3D50 with the Einstein 640 and for the sync the cybercommander. Normally a Hasselblad will sync till 1/800. With my combination the max syncspeed is 1/250, when I use a higher syncspeed, the amoount of light will become less. Anyone else with this problem and is there a good solution to reach the 1/800?

What power are you using on the Einstein? I would be less surprised as power goes up, and not terribly surprised at full power.

Generally, flash is not regarded as being affected by shutter speed because the flash durations are typically shorter than x-sync speeds, which are the limiting factor in focal plane shutters.

The reality is a flash pulse takes a finite amount of time, and if the shutter closes before the end of the flash pulse, you will get less light. Presumably, the faster the shutter speed, the further before the end of the flash pulse, the less light you capture (all else being equal).

This is most notable in leaf shutter systems, but can still be true in focal plane shutters if the flash duration is longer than the x-sync speed (actually, it has to be longer than ~1/2 x-sync, as half of the actuation has occurred before the signal is given to fire the flash).

At this point, the exposure from flash will be influenced in a similar way continuous light is. It will not be identical, since flash light is a pulse that fades out vs. a continuous flat intensity from continuous light source.

As you dial your E640 down, the flash durations get shorter, and the effect of shutter speed should diminish or go away entirely. With other flash units, you would see the same problem at full, and the effect get worse as you dial power down.

The Cyber Commander is introducing a small 1/4000 delay (most radio units have more latency.)

This should have little effect at 1/800. The E640 t.1 time at full power is 1/583 as I recall. So using it at full power should only result in an exposure loss of around 1/4 f stop compared to lower shutter speeds . . . maybe 1/3f with the CC.

At power levels below -.5f you should see no loss.

Of course, there's the possibility the Hasselblad itself may have some delay between shutter opening and flash sync command?

Without knowing your camera settings, I'll make the obvious suggestion. Be sure that you are not shooting at rear curtain sync. If not, try syncing with both a cord and then with the camera flash to trigger the steins to see whether you experience the same result/latency. If so, try/rent another lens, with fewer actuations, if the problem persists, the issue is likely the body's shutter release. I have a H4D50 and use 1/600 and 1/800 Tv all of the time in a studio with the lights at about 1/2 power or a little more.

Ken
kenrichmond.net

One other thing. If your custom settings include "True Exposure", it must be turned off. In True Exposure, the camera is looking to adjust either aperture and shutter values to factory ideals, so that if you are shooting Aperture Priority, and you are set at
1/800 Shutter, the camera has nowhere to go, so it will stop down, leaving you unintentionally under exposed.

Ken

kenrichmond.net