Lighting Ratio

[doidinho]

Quick and easy question for an experienced studio photog today. Assuming the use of two flashes, is the lighting ration the ratio of the cumulative light from both flashes and the fill flash or is it the ratio between the main and the fill flash? Seems like cumulative/fill would be more appropriate for angles between flashes of about 110 degrees or less and that main/fill would be more appropriate for angles between 110 and 180 degrees.

[tim]

Between main and fill AFAIK. Doesn't much matter though, use your meter and use trial and error until things look how you desire.

[Lotto]

I am going to need a diagram to understand the 110 and 180 angles :)

I've seen people use both ways, I would say both are correct.

[PacAce]

Quick and easy question for an experienced studio photog today. Assuming the use of two flashes, is the lighting ration the ratio of the cumulative light from both flashes and the fill flash or is it the ratio between the main and the fill flash? Seems like cumulative/fill would be more appropriate for angles between flashes of about 110 degrees or less and that main/fill would be more appropriate for angles between 110 and 180 degrees.

It could be either a ratio of main to fill or a ratio of highlight (main + fill, if they overlap) to shadow (fill). As long as whoever is looking at the numbers know which one it is, it really doesn't matter much which one is used.

[Wilt]

Quick and easy question for an experienced studio photog today. Assuming the use of two flashes, is the lighting ration the ratio of the cumulative light from both flashes and the fill flash or is it the ratio between the main and the fill flash? Seems like cumulative/fill would be more appropriate for angles between flashes of about 110 degrees or less and that main/fill would be more appropriate for angles between 110 and 180 degrees.


Source intensity is merely reading one light at a time...e.g. if A is Main and B is fill, and A reads f/11 and B reads f/5.6, the intensity ratio is 4:1

For subject contrast ratio, it first depends upon how the light falls on the portion of the subject which is visible to the lens relative to the coverage of the Main area

Using the above intensity ratio, and with Fill covering the full area seen by the lens and with the Main overlapping some of that, the ratio is...

Main: Fill = 4+1 : 1 = 5:1

...but if the fill does not fall on the same part of the face as the Main, then the ratio (for the same light source intensity!) is...

Main: Fill = 4:1

[doidinho]

OK, this makes sense.