Glad I could provide some help. The explanation made less sense than I had hoped it would when I reread it, LOL
By the way, going back to the original post...
Quote:
|
Many elements can throw off exposure...fool the in camera system.
|
...this is doubly true with the advent of all the different kinds of complex metering systems being used today.
Center-weighted, and spot still assume "18% grey" (won't get into the whole "the in-camera meter value is really closer to 12%" thing), regardless of what they're pointed at; this is why you can center-weight off of your hand under the light, open up one stop, and be reasonably close to the "correct" exposure, if not dead on it. These are relatively easy to fool, but they are fooled
consistently and
simply, which means it is easy to understand and correct the exposure based on readings taken with these systems.
Matrix metering (dubbed "Evaluative" by Canon, and also called "multi-pattern"), however, tends to perform other things outside of the usual "assume it's '18% grey'" routine used by the other meters. I half-jokingly refer to the things done as "voodoo". Basically, the meter uses a ton of sensing points (current Nikon cameras use 1005-pixel and 420-pixel meters) to survey the scene and take an average reading- sort of like an average meter that reads the entire frame. This sounds simple enough, right? Except, it doesn't stop there; this where the voodoo comes in. The meter compares the scene to other scenes- stored as exposure data programmed into the meter circuits- and tries to guess "what" you are shooting before making an adjustment; if the camera thinks you're shooting a snow scene, it'll adjust the exposure differently than if it thinks you're shooting a person in front of a bush, etc.. More recently, the some cameras also take color into account, and this means another adjustment based on whether the camera sees red, green, and so on. The reason I call this voodoo is because you really only have a general idea of what the camera is doing to arrive at the final exposure value displayed, and while it is very often "correct" the times it is wrong you don't always know why/how the camera got to where it did.
I really did not quite grasp exposure metering and how to compensate effectively until I stopped using matrix metering and switched to center-weighted and spot. I want to play with matrix metering some more, but each model Nikon I have behaves slightly differently from the others, which means one basically has to profile his or her camera's matrix meter in relation to the camera's tone curve.