Paul C. Buff, Inc. Technical Forum

I just did a test to see what output from an E640 would support the burst rate my 5DIII is able to accomplish.

Test was simple, I setup an E640 with 8.5 reflector approx 10 feet from test subject, then set camera to ISO 100, 1/200 shutter and an F stop that got proper exposure. Exposure was determined by just eliminating blinkies in white square on color checker. This also provided a means for determining shot to shot exposure consistency.

First series was at 40Ws setting in Action mode. 6th shot in burst was .4 EV less than first.

Second series was at 160Ws setting in Action mode. 6th shot in burst was 1.5EV less than first.

The intermittent images look like the power output was constantly diminishing over the range.

Since the flash duration is short enough to ensure no black frames is the consistently diminishing output the capacitor slowly running out of power?

Yes, sort of. It is the capacitors running out of power, and not able to recycle to replenish. However, 40Ws should be low enough to support 10fps if running from a wall outlet. Running from a VML, that number would need to be lower. What frame rate were you trying?

That explains it. I was using a VML that hadn't been charged for awhile and was less than half power in battery. I think the frame rate on the 5DIII is something like 6FPS in raw.

The charge capacity of the battery would not really affect the frame rate, as the battery discharges a relatively constant power. However, the recycle times on a vagabond mini will be slower than that of a standard wall outlet. 14Ws or so should keep up with 6fps from my testing.

Makes sense. Thanks.