How do you take a picture using a manual camera?
Most negative films are forgiving, especially B&W films like Tri-X and FP4+. You can be 4 stops off and still get a workable frame with films like those. Even color films like Ektar and Pro 400H have tons of latitude.
It's only with slide film (or digital sensors) that you really need a meter. But let's be honest: I have a meter app for my cell phone which I use to double-check my manual metering. A light meter is a great training wheel, because it's annoying to use, and this annoyance will encourage you to use the meter less and less.The Leica M3 has no electronics whatsoever. Metering is 100% manual.
But the good news: you don't need a meter. The Sunny 16 rule is real. It works. In bright daylight, you can reliably set the aperture to f/16 and the shutter speed to the reciprocal of the film's speed. (E.g. with an ISO 100 film, set the camera to 1/100 shutter speed; for a 400 ISO film, set the camera to 1/400 shutter speed.)
When things aren't bright daylight, you just have to memorize a few more rules of thumb, at least to get started. Once you've done it for a while, it becomes more second nature.
- Start with daylight of f/16
- Drop 4 stops for outdoor shade, or an overcast sky, or dusk
- Drop another 4 stops for darker versions of those
- And sometimes, when it's just plain dark, you just shoot wide open at 1/60th, and hope it works. But really, when it's too dark to meter, it's usually also too dark to focus.
To train yourself, just start testing yourself. Look at a place, guess what your exposure would be, and then check your answer on the light meter.
But the best part is...
The best part is, once you get the hang of doing the manual "even" metering, where you're trying to meter the entire scene, you start realizing that you don't always want to meter the entire scene evenly. Sometimes you want to meter just a specific part of your image, and intentionally under or overexpose the rest of your frame. When you meter with just your brain, selective metering now becomes second nature, and there are no camera menu options or settings to change.