Vivitar 285hv as slave exposure problem

Hello. I have non consistent flash exposures using Vivitar 285hv. In next example, camera in manual mode, 430ex as master flash on hot shoe in manual mode, 1/16 power, bounce, optically driving Vivitar 285hv set to bounce flash to the ceiling at 1/2 power, about 5 meters from my subject.

Camera is set to continuous shooting at slower speed, and these two images are from the same burst, one after another. What do you see here? Images are too much differently exposured by Vivitar. More exposed image is from first shot in burst sequence and darker image is from second shot. I tried of course just with 430ex and then bursting give consistent exposures, so, Vivitar is the one that make difference.

It happen all the time, first flash in burst sequence has always much more power than following flashes.

Faulty flash or this is normal?

Thx

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Maybe your not giving the Vivitar enough time to recycle...

Normal manually set off your 285 and watch the ready light and time it to see how long it takes to recycle. At 1/2 power mine takes about 4-5 seconds right now with not so fresh batterys not going to keep up with any burst mode. Hope this helps John

OK that explains this differences. I should wait more between shoots. Thanks.