# Doubling speedlights = doubling power??



## RockstarPhotography (Mar 16, 2011)

I've always shot with 2 speedlights on my stand.  Mostly so I can crank the power down and still get fast recycle times and longer battery life.  I've never really had the need for large amounts of power.  I'm looking at doing a shoot where I may need to start overpowering the sun.  To me it makes sense if you double up speedlights, you would effectively double the power, If you triple them, you would triple it.  Is there something I'm missing though?  I'm no scientist, but that seems logical.  I'm asking because if i can't get the power I need from at least 4 speedlights i may have to look into renting a strobe.


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## Robin Usagani (Mar 16, 2011)

Yeah...  double the flash, double the power.


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## benhasajeep (Mar 16, 2011)

If you add a 2nd flash you will get 1 stop more light (if both fire at full power).  To get 2 stops of additional light from a single flash, you would need to go to 4 flash units (at full power).

One thing about using double flashes is if they are not firing at full power, say each at 1/2, you do get the same result as 1 flash at max.  But they will recycle quicker since they did not have to fire full power.  But just like any exposure setting.  To get more light you have to double the previous (for a full stop of additional light).  So it would be 1 light, 2 lights, 4 lights, etc.  Each step up in quantity of lights gets you another stop of light.


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## RockstarPhotography (Mar 16, 2011)

so if the gn on my flashes is 38.  If i fire 4 of them do you think that would be enough to overpower the sun or should i go rent a strobe?


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## benhasajeep (Mar 16, 2011)

RockstarPhotography said:


> so if the gn on my flashes is 38. If i fire 4 of them do you think that would be enough to overpower the sun or should i go rent a strobe?



Deppends on distance.  Closer you are the stronger they are.  Not sure if you mean sun in the background, so your wanting to make sure you have enough fill flash?


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## Big Mike (Mar 16, 2011)

As mentioned, you do double your light when adding a 2nd flash (both the same and both firing at full power)...but that's really on one stop more light.



> so if the gn on my flashes is 38. If i fire 4 of them do you think that would be enough to overpower the sun or should i go rent a strobe?


Too many factors to give an answer yet.  As mentioned, getting the lights as close to the subject as possible, will really help.


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## 480sparky (Mar 16, 2011)

1 speedlight = 1 unit of light.

2 speedlights = 2 units of light ( or 1 full stop ).

3 speedlights = 3 units of light ( or 1½ stops ).

4 speedlights = 4 units of light ( or 2 stops ).


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## gsgary (Mar 16, 2011)

RockstarPhotography said:


> so if the gn on my flashes is 38.  If i fire 4 of them do you think that would be enough to overpower the sun or should i go rent a strobe?



No, unless it is very dull


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## RockstarPhotography (Mar 16, 2011)

I'm planning on doing a shoot mid day tomorrow during some nice harsh light.  Haven't really decided what kind of shots i'll be taking since i usually just wing it, but probably something with the sun behind her and flares, and maybe trying to drop the ambient way down so if feels more like dusk and filling her with some flash.  I want to try it out with 4 flashes, but don't want to get stuck not having enough power, Even if I rent a strobe i'm going to try it with flashes first just to see.  The location we have does have some shade here and there so I won't have to completely drown out the sun.


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## gsgary (Mar 16, 2011)

You could also use an ND grad filter to drown out some of the sunlight


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## benhasajeep (Mar 16, 2011)

I would think 4 would be enough to fully light her.  If anything you might just have to move them a little closer.


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## GeneralBenson (Mar 16, 2011)

Don't forget that even with enough flash power, you still need to do something to knock down the sunlight. Unless you are shooting in FP/Hypersynch/blah blah mode (which will squash you flash power and require even more flashes), then you are locked at your 1/250th sync speed. So at midday, with full sunlight and ISO 100, you're still probably looking at an aperture of f/8 - f/11. So unless you were looking for that kind of DOF, which is the easiest solution, you need to do something about the rest of that light. Gary also mentioned the use of ND filters to get rid of the sunlight. If you want a shallow DOF shot, like at 2.8, then you basically 3-4 stopd of light that you need to cut down. For such situations, I have a 2 stop ND filter and a polarizing filter, which is good for about a 1.5 stop loss. So that gives me the options of 1.5 stop loss, 2 stop loss, or 3.5 stop loss if I use both, with the added benefits of a polarizer, which can further help darken the sky, if the conditions are right and you're facing the right direction.

As for doubling you power, as hasalready been mention, due to the Inverse Square Law, you always need to double whatever your current power level/number of flashes is to get to the next stop. So if you have 1 flash, and you need 2 stops more power, you would double it to 2 flashes for the first stop, then double that to 4 flashes for the second stop. As it turns out, a stop isn't a huge difference and it adds up fast. It's not uncommon to find yourself in situations where you realize that you would need 8-16 flashes to pull off the shot you want. That's where big lights come in, but the same rules apply. If you have 400 W/s, and you need another stop, then that's 800 W/s. Another stop over that would be 1600 W/s. And all of the sudden you begin to realize why it's quite simple to be in want of $8000 of lighting gear. 

Good luck!


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## Village Idiot (Mar 21, 2011)

RockstarPhotography said:


> so if the gn on my flashes is 38. If i fire 4 of them do you think that would be enough to overpower the sun or should i go rent a strobe?



And if you're using any modifiers at all, they'll eat light. I was having problems overpowering the sun with a beauty dish and 400w/s under harsh bright noon sun.


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