Nine out of ten submini cameras do not have a built-in meter. They were designed to be small -- and one of the first things to go was the built-in exposure meter. Not to mention that a lot of submini cameras were built BEFORE built-in exposure meters even existed!
To deal with exposure, subminis use different techniques. Most subminis were designed to be used in specific situations -- usually sunlight. So they were able to make their cameras even simpler. Many went even further and designed the cameras to be used with specific film -- typically ASA 100/125 speed film. This is why many subminis have a fixed shutter speed and a fixed aperture. If you know that the film (ASA 100) will be exposed in sunlight, it will always be the same shutter speed and aperture. This makes for a very simple camera design. If these exposure settings are built into the camera and the exposure is made in these conditions, the result will always be correct.
But some subminis were designed to be used in different situations other than sunlight, and some were designed to be used with film other than ASA 100. So their cameras had to have variable apertures and/or shutter speeds. And some have both. The problem is that these variable exposure cameras do not usually have an exposure meter built in. So how can you easily set the correct exposure without a meter?
Actually, it's not too difficult. The place to start is the f-16 rule. This rule states that the correct exposure for a sun-lit situation is f-16 (hence the f-16 rule) with a shutter speed that is the reciprocal of the film speed. In other words, on a sunny day set the f-stop to f-16 and the shutter speed to the film speed.
Let's say you are shooting PLUS-X (ASA 125). On a sunny day, set the f-stop to f-16 and the correct shutter speed will be 1/125. Everytime. If you are shooting TRI-X at ASA 400, the correct shutter speed is 1/400 at f-16. Now your camera probably does not have 1/400, but 1/500 is close enough. PANATOMIC-X (ASA 32)? Use 1/30 at f16. You can't lose.
But what if your camera doesn't have f16? What if it's a HIT camera set at f11? Or what if you want to use a different shutter speed. That's OK, just change the aperture and shutter speed in tandem to compensate. Let's take our PANATOMIC-X (ASA 32) example. The f-16 rule says f16 at 1/30 on a sunny day. If you are using f11, just set the shutter speed to 1/60. Just what a HIT camera calls for since it has a fixed shutter speed of about 1/60.
And what about situations other than a sunny day? It's easy. If the sun is hazy but still creates some shadows, open up to f11. If the day is bright, but no shadows are cast, open up to f8. If the day is cloudy, open up to f5.6, and if it's stormy, open up to f4.0. If you are inside, but there is some outside daylight coming in, open up to f2.8, and if you are inside at night with bright light bulbs, open up to f2.0. Now, I know that most cameras don't have f2.0, so you compensate with the shutter speed instead. Let's say, your lens goes to f4.0 at 1/30, but you need f2.0. Set the shutter speed to 1/8 at f4.0 instead. And I also know that 1/8 is too slow a speed, or your camera may not have 1/8. In this case, you'll need to switch to a faster film. After all this is a dark situation. If you switch to ASA 125, you'll be able to shoot at 1/30 with f4.0. For dark situations or a faster shutter speed, switch to an even faster film.
But this is only a cheat-sheet on exposure. If you want to learn what exposure is really all about, follow this link.
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