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The buttons you press on a camera to produce the right exposure in low light, are all the same as when you shoot in the middle of the day; the same rules of exposure apply, it's just a little harder to get there. When there's less light in a scene, you have 2 choices; either you create more light yourself or you change the settings on your camera to react differently to the light available. This tutorial is all about how to do that.
Exposure
If you've not read the tutorials inside my Understanding Exposure blog post, then I strongly suggest you go back and read them now – there's a lot more to it then you may think. Putting that aside though, you basically have 3 ways of getting more light into your camera in a low light situation; aperture, shutter speed and ISO.
Aperture
This is the hole the light passes through in your lens and the wider it is, the more light it lets in. Rather confusingly, the wider the aperture, the lower the f-number, so bear that in mind. This step isn't particularly useful if you're still using your standard kit lens as you'll find that your maximun aperture is somewhere around f/3.5, which won't let in enough light to really help out. What I suggest is to buy a cheap, but effective prime lens with a maximum aperture of about f/1.8 (Canon EF 50mm f/1.8 ii) – this is commonly referred to as a 'fast' lens as it allows you to take photos at faster shutter speeds. The photo below was shot on film but if i remember rightly, it was f/1.7 for 1/30 of a second at ISO 200.
The point here is that if you want to take a well exposed photo in low light, you need to have a lens with a wide aperture as it lets more light in. Setting your lens to stop at f/1.8 actually lets in 4 times more light then f/3.5, which is a huge difference for a small change in number. A wide aperture will produce a shallow depth of field though, and there's no way around that, unless you make your aperture narrower again and increase the ISO or slow down your shutter speed.
If you're taking photos of groups of people in the pub or somewhere, be careful about how wide your aperture is because you'll end up with half the people not in focus. This is a good time to use the flash, but take my advice and invest in a proper external flash unit, it'll make a world of difference.
Shutter Speed
Shutter speed is step 2 in creating an exposure and also affects how much light enters the camera – the faster the shutter speed, the less light that will enter the camera. If you're out and about in a low light situation, chances are you're not going to have a tripod with you, so you'll have to be careful not to select a speed too slow or you'll end up with blurry photo.
As a rule of thumb, the average person can take a sharp, blur-free image by setting the speed to a fraction of a focal length. For example, to take a photo at 30mm, you would set the shutter speed to 1/30 of a second; any slower and motion blur is likely to occur. It’s worth noting however, that this rule is only relevant to full frame cameras. For a crop sensor, due its magnifying effect, you would be better off choosing a speed of 1/45 of a second and you'll need to drastically increase your shutter speed if the subject is moving.
If you happen to have a tripod with you and you're shooting a still object, then you have the ability to make the shutter speed virtually as long as you want. What I recommend is shining a torch on your subject so that you can focus properly and using an external shutter release trigger to minimalise camera shake.
Another technique worth trying is using a relatively long shutter speed in a crowd of people and capturing their motion blur while the objects around them remain still, like in the photo below.
ISO
This is slightly more tricky to manage on most cameras as the higher the ISO, the more digital noise there will be, and this can be pretty ugly. If you're struggling to get the exposure you're looking for with just changing the shutter speed and aperture, then the best thing to do is to raise the ISO. Remember how stops work though, if you double the ISO number, you're doubling the amount of light that your camera is seeing.
I find that high ISO's on my camera aren't very good at determining colour so you might want to consider changing your photos to black and white. That gives the photos a nice warm and old feeling to them and the high ISO actually adds to this. Typically though, I don't raise my ISO to anything further then about 1600 – if i need more light after that, I use a flash unless i'm doing it for artistic effect like the photo below shot at f/2.8, for 1/8 of a second at ISO3200.
Low Light Photography with a Flash
When you're shooting groups of people in low light, it's best to use a flash. As I explained above, if you don't have your aperture too wide, you're going to end up with a shallow depth of field and not everyone in focus.
If you only have a pop-up flash on your camera, then you're limited with what you can do with it really, but some of these techniques will still apply. Firstly, just because you're using a flash, it doesn't mean that you can set your ISO all the way back down to 100, because if you do, you'll start to lose background detail in the dark. I like to make leave my ISO on about 400 as I feel it's an acceptable amount of grain and detail – all cameras are different though so play around with yours to see what you're comfortable with.
If you're using an external flash then it's best to bounce the light off of a wall or ceiling or to use a diffuser to make the light look a lot less harsh. A lot of the time when a flash is used properly, someone who's not really into photography can't even tell that a flash has been used, which is exactly the reaction you want. Image below was taken at f/5.6, 1/50 of a second at ISO 500 with the flash bouncing off the ceiling. 
Playing with light trails can produce some really cool results, and all you have to capture this is to take a photo of someone with a flash pointed directly at them, and have the shutter speed long enough to capture the blur that comes afterwards. Have a look at my example below taken at f/11, for 5 seconds, at ISO 100.
Tips
Here's some tips to bear in mind when you're using your camera in low light conditions:
- If you're in a dark room and you want your photo to accurately capture the environment you're in, the photo should be a little bit underexposed.
- Getting the photo take priority over worrying about ISO noise.
- Keeping your elbows together and not leaning forward will help you to hold the camera steady for longer, allowing you to lower your shutter speed.
- Turning up your camera's exposure compensation will help your camera to overexpose, and in darkened conditions, produce more accurate results.
If you have any questions or tips of your own, please feel free to leave a comment and we’ll get back to you.
