YN565EX multi mode

[vRSG60]

I've just taken delivery of a Yongnuo YN565EX flash gun to use with my D90. This unit has "multi" mode. I can set the flash power, frequency (flashes / second) and number of flashes per activation.

Can someone explain the relationship between my shutter speed (say 1 Second) and the other required settings.
Let's say i wanted 3 flashes at 1/2 power using a shutter speed of 1 second what would I need to set the frequency as? 3?
What would the frequency setting be for 3 flashes over a 2 second exposure? 1.5?
Or if the flash is on camera will it just hold the shutter open for the specific duration to suit the settings?

As I see it number of flashes divided by the frequency = shutter speed. So number of flashes/shutter speed = frequency.
So 3 flashes using a 1/160 shutter speed = 480 frequency.

Also will it work if I was to use this off camera using triggers. (Which is why I'm trying to calculate shutter speed).

 

[coldpenguin]

Hmm, you haven't had any replies.

I have a canon 580 EXII, so, you may need to take some of this with a pinch of salt.
Yes, you should set the frequency to be multiplied by number of flashes to be equal to the shutter time.
So your calculations are correct.

However, you could in theory reduce it slightly. With 3 flashes, at a frequency of 3 Hz, in theory they should complete in:
(1/freq)*(n-1)+ a jiffy
I.e., there should be 1 flash, then, a wait of 1/(freq) seconds, then another flash, then a wait of 1/(freq) seconds, until the number of required flashes. So in 1 second+ a jiffie, there should be freq+1 flashes.

On the canon at least, the flash will not hold the shutter open.

The canon will work with off-camera trigger, either optically or wireless. In theory, the E-ttl might also be available, but I would set it manually anyway.

I always found multi-exposures difficult, the background was diffficult to get correct compared to the foreground. However that was with the flash on-board and my old camera, my new one has a much better flash control system. I don't know what you are expecting to take pictures of, but I spent a long time with a remote control, and walking across the field of view to practice.

 

[vRSG60]

Thanks for the reply.