But an DSLR has a suface area of exposure. So 100% magnification on a small DSLR chip will not be 100% magnification on a 4x5 is an example. Exposure compensation for macro work can be based on magnification.
Originally Posted by Steve Smith
Also, I wouldn't assume that chimping on an LCD screen will give accurate exposure either. A chip on a digital camera has a different exposure curve than a piece of film.
As other APUGers posted, nothing beats a spot meter and knowing how to use it.