Basic camera light meters are good for grabbing memories on the run. But the more I photograph, the more I realize that they only get the photo I'm looking for about 1/3 of the time! They average the light in the frame and give you a compromise exposure. Safe, but not always effective.
Here's one, for example, where I knew that I wanted the person's skin to be lighter than average, and it's the darkest part of the photo:
With the white background, the meter would have made the skin much darker than normal, but that's not what I was going for (sorry I didn't do a darker one for comparison).
Ansel Adams had an approach that he used mostly with black and white called the zone system. This is what many people shooting with meter-less cameras, especially large format, use. A spot meter is used to take readings of very specific, small areas of the composition to be photographed, and those readings are placed on a sliding scale from dark to light (oversimplifying to say 0-10 from dark to light, but we'll use that). A typical wide area light meter determines an average for the equivalent of 5 (in the middle). In the photo above, her skin would have come out to about 3 or 4 because the background would have been about 6 or 7, and the two would have been averaged. In the actual photo above, the skin is about zone 5-7 or so, and the background about zone 9.
Below are four photos of the same subject with different exposures from average to darker, each separated by the equivalent of one full f-stop on the camera (which is roughly equivalent to one step on our 0-10 scale).
1/30 sec @ f/2.8
1/60 sec @f/2.8
1/120 sec @f/2.8
1/250 sec @f/2.8
The first photo was the camera meter's average. Great for a snapshot. But what if you wanted the grass and the white box exposed better? Halving the exposure is a step in the right direction, and the grass is more naturally green. The third and fourth photos put the box in about zone 4-6, at the expense of the darker background.
OF COURSE THERE IS NO OBJECTIVE CORRECT EXPOSURE, just decisions on what the photographer and viewer may be looking for.
So, these are not great artistic examples, but good enough to explain the basics. Why am I concerned with this?
My large format camera has NO meter in it. I use a spot meter to meter the grass, tree trunks, background foliage and the box separately and then decide where to lay them out along the zone system scale of 0-10.
However, I'm not that experienced at doing this and judging where on that scale each item should be located.
So, I've pledged to spend some time PRACTICING! What I am doing is taking my spot meter out and making educated guestimates where parts of a scene go when visualizing. Instead of wasting lots of film in practicing, I am using my digital camera in MANUAL mode, and testing out these guestimates to experience what the results actually are.
This is harder than it might sound. Eventually, however, it will help me to be more confident when spot metering with the film camera, and more adventurous with the digital camera.
Just like I pretty much don't use the automatic focus on my digital camera anymore unless it's a fleeting moment. I can focus better and quicker doing it myself!