Many people have great cameras but never take them out of Auto mode. In Auto, the camera’s built in intelligence will set your shutter speed, aperture, and ISO for you, and take a decent looking photo. All you need to do is compose your shot.
Moving beyond Auto, many people use Aperture Priority, in which you set your aperture, and the camera will set the other parameters. Or you can use Shutter priority, in which you set the shutter speed and let the camera choose your Aperture. With Aperture priority, you are able to decide how wide the lens opens, which alters your depth of field; with Shutter Priority, you can ensure that the camera always takes the shot at a speed that minimizes (or perhaps maximizes) blur.
But… c’mon. You’re not here to do everything on Auto, or even Aperture or Shutter priority, are you?
Of course not.
To exercise more control over your photography, you need to know what each of the settings – Aperture, Shutter Speed, and ISO – mean, and how they affect your results. You are always going to be balancing the effect of these and knowing what is likely to happen when you change one is critical.
- Aperture: how wide the lens opens when you take a shot. Wider = more light. But wider also = shallower Depth of Field, or DOF.
- Shutter Speed: how long the shutter remains open when you shoot. Higher number (say, 1/125 vs 1/60) means less light. But it also is better at ‘freezing’ action and preventing blur.
- ISO: The sensitivity of the camera to whatever light is present. High ISO = greater sensitivity. But higher ISO also means more “noise”, which shows up as a grainy quality.
- On a bright day, if you want to isolate your subject by blurring the background (shallow DOF), you have to deal with the resulting extra light – maybe reducing ISO and/or increasing shutter speed.
- In dark conditions, getting a deep DOF – meaning a narrow aperture (i.e., higher F stop) – will mean you need more light. You can reduce the shutter speed, but you might get blur. Or you can increase the ISO, but you will get graininess. And if it is very low light, you may need to do both as well as using a lower F stop. To keep the shutter speed down, you will need a tripod to prevent blur – but if your subject is moving, that won’t work.
It’s all a balance.