Third Step:

Controlling the specified amount of light hitting a specified medium, a.k.a controlling the medium sensitivity or ISO.

You have mastered the arts of aperture and shutter speed. Heck, you can even tweak the settings to its best without batting an eyelid. But no matter how good you are in adjusting apertures and shutter speeds, it won’t do you any good if you can’t capture the moment. After all, what is the point of changing settings here and there when you don’t actually take photographs? This is where the medium comes into rescue (no, not that chanting old lady with Tarot cards;)

You see, the medium here is where you capture your light. Or, to be easier, a normal 35mm negative film is a medium. Or sensors for digicam. Get the picture?

Basically, a medium has sensitivity to light. What does it mean by this? Its sensitivity is determined by how much lights are required to produce an image on the medium. The sensitivity scale is known as ISO (or ASA, for Americans), which is an acronym for International Standard Organization.

You might remember the good ol’ film days, where you bought films by their numbers, i.e 400 films, 200 films, and 100 films. That is what you call the sensitivity scale. The higher the number, the more sensitive it is to the light.

That is the same for sensors in digicam. The big advantage of digicam is that you can change the ISO setting on the fly, unlike films where you would have to finish all 36 pictures in one roll or forfeit the balances in order to change film.

You can also use faster shutter speeds with higher ISO, to avoid blur in your pictures.

But what about disadvantages?

Unfortunately, increasing the ISO also increase the noise. What the heck is this noise? It is basically an unwanted collection of tiny white or gray dots in your picture that is the result of increasing the ISO. This is especially visible in shots taken in low light conditions, where you might noticed that your picture has many tiny weeny little dots in it.

The ISO scale started at ISO 25, and goes to as high as ISO 6400 and more with certain amount of incremental values. For normal lighting conditions, it is advised to use ISO 200. Or for a very bright day, ISO 100. Go beyond ISO 800 in low-light conditions, and you’ll start noticing noises in your picture.