> -----Oorspronkelijk bericht----- > Van: Ramesh Kumar [mailto:[EMAIL PROTECTED] > > > Here is a scenario. Assume you are shooting a > reflection of sunlit tree; reflection is occupying > full frame. Water is dark except for the reflection. > > When I spot meter for dark subject, I do -2 stops to > get %18gray. > > Going back to above scenario, If I SPOT meter the > "reflection of sunlit tree", should I have to > compensate by -2? > > Basically, should I have to do anything special > compensation just beacuse its reflection. or should I > treat as any other shot? > > Thanks > Ramesh > Dear Ramesh, Some thoughts about your problem: In general, a "normal" scene would contain "normal" blacks and "normal" whites. Normal black has a reflectivity of let us say: 2% Normal white has a reflectivity of 100% This means if you light this scene with a soft box (clouded sky, the light is not adding contrast) the contrast ratio of the scene would be 1:50. Your film (depending on the type) can handle this contrast ratio. To minimize grain, you donot want to overexpose, so you want the black (of 2% reflectivity)just on the beginning of sensitivity curve of the film. If, for your film with your development process, this point is 3 stops below the suppliers ISO rating of the film, you could do a spot metering of the 2% black and set your camera to an ISO setting 3 stops below the film ISO and you will have the right exposure!
You might as well measure the light of a gray card with 18% reflectivity, and use the suppliers ISO rating. This would give the same result because 18% is almost 3 stops above 2%! If, in the above example, you want to see details in black of 1% reflectivity you have to increase exposure with one stop. Your contrast ratio now will be 100:1, the film can still handle. If your scene has abnormal black, for instance a "black hole" with 0.1% reflectivity, the contrast ratio becomes 1000:1, your film will not be able to handle, and you have the choice: details visible in the blacks or in the whites, but not both with this film. In case of light reflections on water or on leaves, they sometimes act like little mirrors reflecting light sources (sun, lamps etc)in this case the light intensity can be 10 times higher than "normal" whites, no film can handle the corresponding contrast ratio! If you try to measure those "extreem whites" you could underexpose the blacks and greys far too much. If I understand your scene well, you donot have the case of abnormal whites. You have a normal scene that is reflected in the water acting as a not very bright mirror, maybe you loose 1 or two stops in this mirror. You should be able to measure the reflected scene like any other normal scene. If you take too much time to analyse the scene on forehand, sometimes the scene is over (sun is gone!), before you are ready to take the picture. In your case I would measure a part of the scene corresponding to 18% grey and expose according to that. If I would think that the picture might be a goody, I would use braketing + and minus one or two stops depending om the type of film. I would never base an analysis on a measurement with matrix metering, as matrix metering is using algoritms unknown to us, it is un predictable (but often very acurate!). Just some of my thinking! Jos
