Monday, June 9, 2008

Using Guide Numbers with Multiple Strobes

This is my final article on using Guide Numbers with external flash units. My goal of these articles has been to help new and infrequent users of their flashes / strobes to get close to a good starting point as possible in terms of exposure. From the starting point it should very quick to get to the exact exposure you're trying to achieve.

I've had a number of comments in the Strobist Discussion forums from people who disagree with using guide numbers to calculate exposures. But in the end I feel that guide numbers - used as guides - give a good estimate. Which is why I've tried to show the "proof of the pudding" in this series of articles.

Using Guide Number tables that I wrote about also allows you to enter in Guide Number that you feel are more realistic and use these for initial setups. I'm hoping to get my hands on a few different light meters and try and calculate a more accurate set of guide numbers - if anyone has a set of GN's that they feel are more "accurate" please send me an email with the details for me to test.

So for this last article I wanted to test the theory of combining flash units and light modifiers and using the Guide Numbers I had calculated in my previous article. So here goes...

Single Flash
1 x 580 EX II flash - Camera Right
Bare light
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten

Dual Flash
2 x 580 EX II flash - Camera Right
Bare light
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten

Duel Flash (CTO-Full)
2 x 580 EX II flash - Camera Right
Bare light with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten


Duel Flash (CTO-Full)
2 x 580 EX II flash - Camera Right
Bare light with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten



Duel Flash - Mixed (CTO-Full)
1 x 580 EX II flash - Camera Right
1 x 430 EX flash - Camera Right
Bare light with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten


Duel Flash - Mixed (CTO-Full)
I thought it was three flash units but one didn't fire
1 x 580 EX II flash - Camera Right
1 x 430 EX flash - Camera Right
Bare light with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten


Triple Flash - Mixed (CTO-Full)
2 x 580 EX II flash - Camera Right
1 x 430 EX flash - Camera Right
Bare light with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten

Triple Flash - Mixed (Stofen)
2 x 580 EX II flash - Camera Right
1 x 430 EX flash - Camera Right
Stofen Filter with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten

Triple Flash - Mixed (Stofen)
2 x 580 EX II flash - Camera Right
1 x 430 EX flash - Camera Right
Stofen Filter with CTO-Full gel
1/250th @f22 - metered for -2 Stops against the sky.
WB set to Tungsten

I hope you have enjoyed reading these articles and have removed the fear many people have of using guide numbers. In the end the above pictures are not perfect but I feel are good starting points for a photo shoot.

Please feel free to leave comments or questions below or email them to me.

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