--- josvdh <[EMAIL PROTECTED]> wrote: > > -----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. >
I guess "extreem whites" mean glare. I was using polarizer and removed the glare. > 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. How max stops of bracketing is normally used for Velvia 100F and Kodak E200?. I guess 1stop max for Velvia and 2stop max for E200. > 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 > Thanks for informative response Ramesh __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com
