Most of this is pulled from my article about using a camera without a light meter. This is a basic layman’s description of how a camera, any camera functions. Keep in mind that any camera works on the same principle of being a light tight box capable of receiving light rays and capturing them on some sort of imaging device, be it film or sensor.
ISO. In regards to Film and digital, the ISO is a way of measuring the speed in which your film or sensor reacts to light. The faster the film or the higher the ISO the less time is required to make an exposure. What you give up for higher ISO is fine grain or low pixel noise. In digital cameras high ISO results in higher noise levels. Modern dSLR’s have greatly improved in this area making it possible to shoot 1600 or higher with little penalty on some cameras. In regards to film ISO can get confusing because the actual speed on any given film may be lower the advertised box speed. You can still get acceptable results using the box speed, but for optimum exposure you may have to stray between 1/3 and 1 stop to get the “true” exposure value of the film. There are some simple but time-consuming tests you can do to find your actual film speed. How you process your film and how you meter (or not meter) has an effect on your negatives as well so you can fine tune your results based on your technique. If you care about this kind of stuff I can’t recommend Ansel Adam’s book The Negative enough. However if you just want the nuts and bolts of manual photography read on. You can always “push” or “pull film to change your ISO. Again, you can refer to the above reference or find numerous other references that discuss this technique, when you should use it and why.
Aperture. All you really need to know is that the smaller the number, the more light a lens lets in. This is commonly known as an F stop. They call it a stop because on many older lenses there’s an actual “click” between settings and it’s common in photography vernacular to refer to the distance between clicks as stops. Some lenses have half stops in between the numbers. Cameras that control aperture digitally may have 1/3 stops. The common settings (i.e f2, f2.8, f4, f5.6, f8, f11, f16, f22) let in exactly twice as much light as the previous setting. When you get at the bottom of the scale the stops may not be in whole increments as an example F1.7 is a little more than one stop below F2.8 and less then a whole stop from f2. Don’t get too hung up on the numbers eventually they’ll either come to you or you can ignore them and go happily on your way.
Shutter Speed. These are measured as fractions of a second. 500 is 1/500th of a second. Beware: Old Cameras lie, for modern camera users this is probably dead nuts accurate. Your old film camera may not be exactly spot on especially if it sat in a box in the closet for 20 years. Luckily film is forgiving stuff. As in aperture each stop lets in twice as much (or half as much) light. So 1000 is twice as fast as 500 so that’s one stop. 250 is 2 times as slow as 1000 so that’s two stops and so on.
All things being equal if you let in less light through the aperture you must keep the shutter open longer to achieve the same exposure. If you let in more light you must reduce the amount of time the shutter stays open. Shutter speed has an effect of motion. The longer a shutter is open the more movement and camera shake is recorded. Aperture affects Depth of Field, the sharpness and contrast of your lens. In the useful range of things the larger the aperture the softer the image and contrast. This is why top performing high-end lenses tend to cost more to make and cost more for you to buy.
