Shooting in Low Light
I often find myself in situations at weddings or museums where the use of flash is not permitted or appropriate. Or even when just shooting candid shots and not wanting to startle someone or ruin the moment with a conspicuous and intrusive flash going off. It’s in these situations that understanding how to set your camera up for low-light shooting can come in handy.
There are three ways to adjust for how much light hits the sensor on a camera. These are the aperture, shutter speed and ISO (read more detailed descriptions in the Basics section. The important thing is understanding how to use them and in what situation.
Now when I talk about pictures in low-light, I’m talking specifically about getting still shots without all the blurriness. The best solution, but also the most expensive, is to get a lens that has a wide aperture (low f-stop number). This allows more light through the lens (bigger hole) onto the sensor. With whatever lens you have, you want to set the aperture as wide as possible (lowest number). I prefer to shoot in Av mode because it adjusts the shutter speed to the aperture I set. If it still looks too dark, I might play with the exposure setting (the -2/+2 bar on the LCD) but this increases the shutter speed and is probably going to lead to some blur. The next step is to increase the ISO setting. ISO is the measure of sensitivity of the sensor to light. By increasing ISO, it makes the sensor more sensitive to light. The drawback of higher ISO is that it means the picture will be grainier. This is why it is so expensive to get lenses with wider apertures because otherwise you have to compromise and sacrifice the quality of your shots with ISO adjustments. If you can't get the shot with your widest aperture and highest ISO, you might have to use that flash. Here's a recap of the sequential steps to try when shooting in low-light:
1. Try a shot at the widest aperture (lowest f-stop number)
2. Try a shot with increased exposure
3. Try a shot increasing the ISO setting gradually higher
On the EOS 20D, you can actually adjust a custom function setting to get an ISO 3200 (H) setting. You can only use this feature in the custom modes (letters). Unfortunately, the Rebel XT does not have this feature. For 20D users:
1. Go into the menu
2. Go to Custom Function (C Fn)
3. Go to #8 ISO Expansion
4. Change setting from Off (0) to On (1)
5. You will now be able to increase ISO to 3200 which will read H on your display
Once you get a hang of these settings, you will get a better sense for what you will need to adjust without even having to test them!
Shutter speed controls the duration of time which light hits the sensor. The sensor will capture whatever information it gets while the shutter is open. This means that unless everything is still, anything that moves when the shutter is open will result in a blur. In some situations you might want this effect, but you’ll probably want a tripod or something sturdy for the camera to rest on, otherwise you’ll get more blur than you bargained for from your hand shake.