I wrote this lesson for someone who bought a P&S camera and wanted to understand the very basics of photography without bothering with secret formulas and snobbish jargon. First I’ll explain and illustrate the three basic variables of digital photography (aperture, speed and ISO sensitivity), then I’ll tell you very concretely what you should and should not do with your P&S camera.
– Aperture is the hole through which light is admitted. It determines 1) how much light will reach the image sensor 2) the cone angle of the bundle of rays that reach the sensor which has an impact on the depth of field. In practical terms, the lower the f-stop number (f/2.8, f/4, f/5.6, etc.), the wider the aperture and the narrower the depth of field. The higher the f-stop number (f/32, etc), the smaller the aperture and the larger the depth of field.
In the following examples, you can clearly see the background goes out of focus when the f number is small (i.e. the aperture is wide).
f/32
f/16
f/8
f/2.8
– Shutter speed is simply the length of time the shutter is open (and the image sensor is exposed to light). Obviously, shutter speed, like aperture, determines how much light will reach the image sensor. It also changes the way movement appears in the picture.
In the following examples, I first froze the movement of water with a high shutter speed; I then shot the movement of water during one second.
1/500
1 sec.
Aperture and shutter speed determine the exposure, i.e. the amount of light that falls on the image sensor. If one exposes the film or sensor for a longer period, a reciprocally smaller aperture is required to reduce the amount of light hitting the film to obtain the same exposure. Now if you have a P&S shoot camera, you most likely have no control over aperture and shutter speed. I just wanted you to understand the basic principles of exposure.
– ISO sensitivity is the sensitivy to light of the sensor. The higher the ISO number (ISO 800, 1600, 3200, etc.), the higher the sentitivity, the shorter the exposure required. The lower the ISO number (ISO 50, 80, 100, 200) the lower the sensitivity, the longer the exposure required. Why is it important? Because the higher the sensitivity, the noisier the picture. Look at the following pictures. The amount of light is the same, but the ISO is different:
ISO 80 (0.6 s)
ISO 400 (1/8 s)
ISO 1600 (1/30 s)
ISO 80 crop
ISO 400 crop
ISO 1600 crop
As evidenced by the photographs, ISO 1600 sucks.
Morality of Photography 101 – Part I:
As I said before, you most likely have no control over aperture and shutter speed with your P&S camera. It is supposed to determine with its light meter the correct exposure. However, you can control the ISO of your camera. DO NOT use the auto ISO function of your camera. Set it manually to 50, 80, 100 or 200. Use ISO 400 when there’s not much light and you have no choice. Anything above that will always suck.
Now let’s go further.