Multiple Flashes...metering/exposure

[josh_thornton]

I've got a shoot I'm planning for this weekend with limited

resources...so here's the deal.

 

I'm going to be doing a shoot in a real low light room, and to light

the room I'm going to use my flash. But since I don't want to have

the 'on camera flash' look, I'm going to fire it multiple times to

different parts of the room while the camera is on a long exposure

(perhaps 30 seconds or bulb). The items in the room won't be moving

and the camera will be on a tripod, so those aren't issues.

 

What I'm wondering is how to meter for a proper exposure when the

flashes won't all be simultaneous. I'll be using a sekonic L-508,

Canon Elan 7E, and 550EX flash.

 

Suppose I meter the amount of light that my flash emits and I get a

reading of (iso 100), f/8, 1/4 sec...if I fired the flash twice into

the same area what would the proper exposure be? What do I do if

the ambient light is say (iso 100) f/2.8, 1 sec and I want to

combine that light for 30 seconds with firing my flash.

 

Overal I'm wondering how to add/subtract light exposures. Any help

would be greatly appreciated.

 

Josh

[illusions photo art studio]

Honestly Josh, ask for a Digital SLR, make a few test shots until you have what you want, write down the settings and then shoot on your 7E and don't forget to use bracketing.. I'm no pro, but I think it should work.

[richard_cochran]

To add exposures, the aperture needed is the square root of the

sum of the squares of the apertures required for each individual

exposure (just like the pythagorean theorem). So if

one flash requires f/8 and another flash requires f/8, that's

sqrt(8*8 + 8*8), or f/11. If you had a flash requiring f/8,

a flash requiring f/5.6, and ambient requiring f/4, it would be

sqrt (8*8 + 5.6*5.6 + 4*4), or f/10.5

[chris m., central florida]

In addtion to manually figuring out flash exposure, remember that you have decent exposure lattitude with film. So if you happen to pop the flash too much, you might still get a decent print out of it.

 

If the cielings are low enough and white, and/or the walls are white, try bounching the flash as much as possible to diffuse your light source. I've tried wht you are doing, and ended up with definite hot spots in the print due to direct flash. Bounce flash worked very, very well.

[medina photography cherry]

Josh,

Since the neither the objects nor the camera (via tripod) will be moved, Why not just set your camera on AV, and use your flash. This will blend the ambient and flash light together. I would actually try and bracket the shot (since you are using film) 0, -1, -2 ambient and keep the flash at ETTL normal. Remember to keep it simple.

[medina photography cherry]

p.s. you should use the flash in a bounce position in this manner.

 

Rob