Should You Calibrate Your Camera's Meter?
As long as we're on the topic of exposure, I want to address the question of calibrating the meter in your camera. As you may know, I am a fan of John Shaw's books; he is an excellent teacher. As you may also know, John is on record advising everyone to run a series of tests to see if their meter truly reads medium when pointed at a medium toned subject.
Years ago, this was very good advice as many analog meters tended to be off by as much as a stop or two from what they should read. Modern all-electronic cameras though tend to be far more accurate and are rarely off by even a third of a stop. If you have an older camera, you may be able to improve your metering by calibrating your meter. On the other hand, if you have a newer camera, what should you do? I believe it is still worth running a series of tests to verify the accuracy of your meter, if for no other reason than to know whether or not to have it serviced.
So, how does one do this test? Load a roll of whatever kind of film you usually use and set the camera to aperture priority. Pick a nice middle aperture, say f/8 and mount your camera on a tripod. Point it at something that looks medium to you in even lighting. Avoid bright sun as this tends to be too contrasty. With the ISO adjustment set on DX, shoot a frame. Then adjust the ISO to one speed less than the films nominal rating and shoot another frame. Do this again for several speeds below and above the DX rating, keeping notes of what you are doing. When you get the film back, lay them out on a light table and see which one looks right to you. If the subject you used for the test was truly medium toned, the one at the film's nominal rating should look the best. Keep in mind though that if your subject wasn't truly medium, you may find a different frame looks best so be careful when coming to any conclusions from your test. If you do decide that you truly prefer a frame other than the DX speed, just remember to manually adjust your ISO to that setting in the future. You may want to test a few films to be sure what you are seeing isn't solely the result of the film as well, although even high-contrast films live Velvia tend to render medium toned subjects well.
If, after running this test you find that your meter reads as you expect it to, at least you'll have the peace of mind in knowing that it reads correctly. Of course, then you will have one less thing to blame your next exposure problem on.