I've been concentrating lately on studio work with strobes. At first, I tried the old "just do it" method, but I wanted to get a little more systematic. I'm not an expert, but I've been exposing and developing film for a long time, and so hopefully I'm not too off base. If I am, please correct me!
We all know that exposure predominately effects the darker areas of the scene, whereas development mainly effects the brighter areas. In landscape photography, you can use a spot meter to place detailed shadows on Zone III, which should lead to bright areas falling on Zone VIII for a normal scene, and you use the exposure and development that'll give you the appropriate film densities for your intended use. If you have a non-normal scene, you adjust exposure and development to compensate. (You don't _have_ to have the bright areas fall on Zone VIII. You can adjust exposure and development to give the overall look that you're after. I regularly let the bright areas fall higher than Zone VIII. Many current films have a very straight line response to more exposure.)
If I had a spot meter that worked with flash, I'd be all set, as I could do the same thing I do for a landscape with a subject in the studio. But I don't have one. I only have incident flash meters.
So the procedure for landscapes with incident meters is to meter sun and shade to find the subject illumination range. You then set the meter to twice the film speed and take a shade reading. That's the exposure, and then you develop according what's indicated by your subject illumination range. (This incident stuff is all Phil Davis Beyond the Zone System.)(See Ken Lee's excellent "The Myth of the 18% Gray Card" at: http://www.kenleegallery.com/html/tech/index.php)
So in the studio, fill light = shade, and fill light + main light = sun, as the brightest parts of the image will receive light from both the fill light and the main light, whereas the shadowed areas will only receive light from the fill.
I did the following test. I set up two MacBeth Colorcheckers on a black flag. Between them, and perpendicular to to the first flag, I added another flag. I placed the main light on the right such that it'd only illuminate the right color checker. I placed the fill light right above the camera, such that it would light both color checkers. I entered twice the normal rating on the meter. For Acros, I knew that the real EI was at least 100, and so I entered 200 on the meter. I then adjusted the lights to give a two stop difference. In this case the fill side got f/5.6 and 1/2 and the other side read f/11.5. That's a standard "low contrast" ratio. I set the camera on f/5.6 and took a picture. I took three more picture, closing down 1/3 stop each.
For the next series, I upped the main light one stop. (3-stop difference.)
Finally, for the last series, I upped it one more. (4 stop difference.)
After I developed the film, I read it with a densitometer.
My EI in each case was 125. (The black square of the chart read at least 0.10 above film base plus fog.) I read the white square on the main light side to check high light density. In the future, I'll set exposure for flash in the studio by setting my meter at 250 and set exposure according to the level of the fill light, trying to remember to apply bellows extension correction if needed. There will be a different development time for each lighting ratio. Thus we're back to the "meter the shadows for exposure and develop for the highlights" maxim.
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Originally Posted by Peter J. De Smidt
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