Flash Duration Question

[JoeKitchen]

If you are working with a twin head and plug each cord into the same pack (one cord to A, the other to B) with the pack operating A:B, will that produce the same flash duration as having the twin plugged into two packs? 

(Assume the power would be consistent from each cell used in both cases.) 

In other words, if you know you need 600 w/s of power, but also a very fast flash duration, would using a twin head connected to one pack with each cell set to 300 w/s produce the same flash duration as connecting the twin to two packs with each pack set to 300 w/s? 

I would assume yes, but I am not sure. 

[FelixWu]

If you are working with a twin head and plug each cord into the same pack (one cord to A, the other to B) with the pack operating A:B, will that produce the same flash duration as having the twin plugged into two packs? 

(Assume the power would be consistent from each cell used in both cases.) 

In other words, if you know you need 600 w/s of power, but also a very fast flash duration, would using a twin head connected to one pack with each cell set to 300 w/s produce the same flash duration as connecting the twin to two packs with each pack set to 300 w/s? 

I would assume yes, but I am not sure.

I could be wrong but I think it's more to do with how quickly the capacitor can empty its charge and fill it up again. In that case splitting the cable on the same pack probably wouldn't help shorten the flash duration.

[JoeKitchen]

I could be wrong but I think it's more to do with how quickly the capacitor can empty its charge and fill it up again. In that case splitting the cable on the same pack probably wouldn't help shorten the flash duration.

This appears to be the conclusion that I am coming to and discovering. 

Oh well, looks like I will have to rent four pack instead of three for this project. 

[gss]

I could be wrong but I think it's more to do with how quickly the capacitor can empty its charge and fill it up again. In that case splitting the cable on the same pack probably wouldn't help shorten the flash duration.

I think the operative word here is "the".  If a pack only has one capacitor, then the argument makes sense, but I think more than one are involved.  I imagine that it varies depending on manufacturer, but Profoto definitely states that a dual head with both plugs in the same pack halves the flash duration.

The ProTwin is a single head with two plugs and two flash tubes. Connect both plugs to one generator and halve the flash duration. Connect each plug to separate generators and get twice as much power or twice as fast recycling time. - http://profoto.com/int/products/pro-system-generators-heads-accessories/heads-for-pro-pro-b-generators/item/protwin

[FelixWu]

I think you are right. There are definitely more than one capacitors. Thanks for pointing that out. And I completely forgot about the ProTwin heads. In that case Profoto could also make a "twin"head for B2?

[UlfKrentz]

If you are working with a twin head and plug each cord into the same pack (one cord to A, the other to B) with the pack operating A:B, will that produce the same flash duration as having the twin plugged into two packs? 

(Assume the power would be consistent from each cell used in both cases.) 

In other words, if you know you need 600 w/s of power, but also a very fast flash duration, would using a twin head connected to one pack with each cell set to 300 w/s produce the same flash duration as connecting the twin to two packs with each pack set to 300 w/s? 

I would assume yes, but I am not sure.

Joe,

It depends on the design of your flash packs. With older or "simpler" construction you might have a longer flash duration when powering with two packs. In general you will roughly double your speed (half time) when using a twin head on a single pack. I´m not very familiar with profoto but if my mind serves me well you have one output that is limited to a fraction of the complete flash energy, in this case you will have an advantage when using two packs if you can stay in this power range vs using part of the max power shared by the twin head. We use broncolor packs, which are easier to dial in - and in addition, they show the flash duration in their display... ;-)

Cheers
Ulf

[orc73]

It will depend on the pack. On the elinchrom ranger quadra the b-plug is faster then the a-plug while delivering less power.

[jvpictures]

on my Broncolor pack it says:

1 lamp 1 x 600 Ws = 1/935 sec
or
2 lamps 2 x 300 Ws = 1/1870 sec

may be different with other makes

[UlfKrentz]

on my Broncolor pack it says:

1 lamp 1 x 600 Ws = 1/935 sec
or
2 lamps 2 x 300 Ws = 1/1870 sec

may be different with other makes

Yes, that´s what I said: In general a twin head will have around double speed, but this was not the question. To make any sense you´d have to list 1 lamp at 300Ws (as the other cord would be plugged into the sec on pack).

Cheers
Ulf

[UlfKrentz]

It will depend on the pack. On the elinchrom ranger quadra the b-plug is faster then the a-plug while delivering less power.

So than you will have a shorter flash duration when deviding the power of a twin head on two packs connected to b.

[gss]

Yes, Elinchrom are certainly different.  You really only are able to reduce flash duration by using the lower power jack of an asymmetric pack.  Reducing power generally increases the flash duration, even for their packs, not just monolights.  The nice part about them is that at full power they mostly have a moderately fast duration if you use an A head.