50% Off Portrait Pro + An Extra 15% For EPZ Members With Code: EPZ421

Can't work it out


rodp 15 1.2k England
7 Dec 2007 10:45PM
I must be having a thick moment, or just thick all the time. For the last few days I have been trying to work out if a lot of low power flashes equals one big flash but to no avail. I just can't get my head around it, can anyone help ?
The question is, if you were in the situation of wanting to photograph a very large scene with flash, would a lot of flashes from one unit (on one exposure) equal the single flash from multiple units with regard to exposure and recording detail. Surely multiple flashes may give an "adequate" exposure but would not bring out detail.
Thanks in advance for any input.
Rod.
Boyd 17 11.2k 11 Wales
7 Dec 2007 10:58PM

Quote:I have been trying to work out if a lot of low power flashes equals one big flash


An easy way to think of it is like this:
Shine a torch on a wall so it makes a circle, now shine another torch of equal power at that circle from the same distance - does the circle get brighter?
No.

There is no accumulative effect.
Krakman 14 3.6k Scotland
7 Dec 2007 11:03PM

Quote:There is no accumulative effect

Errr, actually there is.

If you flash a gun twice, you get twice the exposure which is one stop more.

2 stops required 4 flashes, 3 stops requires 8 flashes, 4 stops is 16 flashes, etc.

I've taken pics in the past using up to 30 flashes to get the exposure I wanted.

That all assumes that the flash is directed to the same part of the scene. If you're moving the flash around (painting with flash) then obviously that changes things somewhat.
Boyd 17 11.2k 11 Wales
7 Dec 2007 11:06PM
Oops my mistake. I'm talking of a single short exposure.
rodp 15 1.2k England
7 Dec 2007 11:09PM
Ah, this is what's confusing me. You are right in saying there is no accumulative effect with regard to the light itself but there is (?) with the recording of the light, I think. But, does the detail increase with the recording of the light?
Rod.
Krakman 14 3.6k Scotland
7 Dec 2007 11:16PM
Ah, yes - I was thinking of firing one flash after another. But the same should apply if the flashes are simultaneous eg. from several flash units. The thing is, after adding the second flashgun the addition of each subsequent flashgun makes less and less difference. 'Improving' the light by 5 stops would require 32 flashguns, and 7 stops would require 128 flashguns...


Quote:does the detail increase with the recording of the light

No, detail doesn't increase, just the overall brightness of the image does. The effect on brightness is similar to opening up the aperture.
mad-dogs 18 2.2k England
7 Dec 2007 11:24PM
I seem to remember that if you use two flash units with equal power and fire both at the same time, the exposure increases by a factor of approx 1.4
rodp 15 1.2k England
7 Dec 2007 11:25PM
I'm thinking more of firing the one gun repeatedly for whatever amount is needed, would the detail remain as in firing it once and therefore underexposed, surely detail is just light and dark and would therefore record as if more guns were added to expose correctly with one flash.
Rod.
mad-dogs 18 2.2k England
7 Dec 2007 11:30PM
Shooting room sets on 5x4 in the days of film, we often had to fire 6K packs between 2 to 8 times to build up the exposure in order to maintain the depth of field required for focus.

Using multi flash is an accepted practice.

Minolta and Broncolour meters have a multiflash setting.
Krakman 14 3.6k Scotland
7 Dec 2007 11:32PM

Quote:I seem to remember that if you use two flash units with equal power and fire both at the same time, the exposure increases by a factor of approx 1.4

That sounds familiar. But I think that it might perhaps be 1.4x the aperture? For example, if you had f11, multiply that by 1.4 and you get f16, which is one stop difference? Or have I got something wrong?
mad-dogs 18 2.2k England
7 Dec 2007 11:39PM
Just under half a stop I think. It's not something I even needed to do, so without setting the lights up and checking, I couldn't confirm.
rodp 15 1.2k England
8 Dec 2007 12:01AM
Many thanks for the input, seeing as I'm digital I'll just suck it and see I think. I was / am just concerned that no matter how many times I fire the flash the detail will not come out, and, I will just get a bright, slightly blurred image. The more I think about it the more I realise that detail is just light and dark therefore it should be recorded with enough flashes, I think. Smile
Rod.
mad-dogs 18 2.2k England
8 Dec 2007 9:14AM
Hear and forget
See and remember
DO and understand!
JohnHorne 16 1.0k
8 Dec 2007 9:59AM
Multiple flashes is a technique I have used successfully in the past when doing macro work. Say my flash gun delivered enough power for correct exposure at f/11, but I wanted to use an aperture of f/22 to increase depth of field. f/22 lets in only one quarter as much light as f/11, so I set the lens to f/22 and fired the flash four times. Just make sure that you use a tripod and that nothing moves between flashes.

A suitable analogy might be to think of multiple exposures on the same frame of film. Four exposures of 1/4 second each gives the same result (assuming nothing else changes) as a single exposure of 1 second.
rossd 18 1.1k England
8 Dec 2007 8:54PM

Quote:if you were in the situation of wanting to photograph a very large scene with flash


I think you may be referring to a technique called 'painting with light' where you leave the shutter open and then manually fire the flash unit numerous times. Obviously you can only do this after dark and it's a case of trial and error but I have seen some spectacular results (I've seen a photo of Stonehenge using this method).

Sign In

You must be a member to leave a comment.

ePHOTOzine, the web's friendliest photography community.

Join For Free

Upload photos, chat with photographers, win prizes and much more.