I’m often asked by those who have recently bought a new DSLR camera what it is I think they should do in order to begin to improve their photography. My answer always has been and probably always will be that learning about your exposure triangle will be the best first lesson. This comment is often greeted with a blank look but it really is the next best step.

Why is this? Well if we can learn how an exposure works, the components it’s made up of, we can begin to use our cameras more creatively, more effectively and it gives us more control over the camera when the auto settings just aren’t cutting it. Modern digital cameras are amazing, it’s undeniable, but even with all the bells and whistles of the best DSLR there are times when the camera won’t get it right. Such as when there is a bright spot in frame, like the candles on a birthday cake or a streetlamp after dark. Because cameras in auto generally measure the light based on an average over the whole frame we sometimes end up with a pretty dark picture. This metering mode can be changed but that’s for another post!

So the only thing to do to get the exposure we want is to change to another auto setting? Nope, probably not. While it will take practice, if we can learn to enter one of the main camera modes you’ll soon be laughing. So this is where the exposure triangle comes in. The most important part about the triangle is knowing that each element affects the other. For example, if I have a good exposure but then want to widen my aperture I need to know that I am also going to increase my shutter speed. Increasing my ISO will increase my shutter speed too and so on.

So what’s it made from? The three elements are ISO (use to be called ASA or film speed), Aperture and Shutter Speed.

ISO

ISO refers to how sensitive to light the camera’s sensor is. This used to refer to the sensitivity of the film being used but the same applies today, just that with a digital camera we can adjust the ISO for each individual exposure rather than having to change an entire roll of film or camera back. So we can make the camera sensor more sensitive to light. Making it more sensitive is great for low light photography where flash isn’t permitted or where it would ruin the atmosphere. Great, but what’s the payoff? The more sensitive the film or sensor the more grainy the image. In film this gave a rather attractive gritty look, digital grain or ‘noise’ is far less attractive but this can still be useful and corrected to a certain degree in editing.

Aperture

The aperture is the size of the opening in the lens which determines how much light we want to allow into the camera. It is measured in stops with each full stop being half the amount of light of its previous stop. The more light allowed in, the faster the shutter speed and lower ISO you can use. So why don’t we shoot with the camera ‘wide open’ all the time, that would give us nice fast shutter speeds? Well, again, there is a payoff. The wider the aperture the shorter amount of distance in the focus point is in focus, this is called the focal plane. So if you don’t care whether or not the background of a portrait or such like is in focus, go for a wider aperture, but for most landscape and cityscape photography having the whole scene in focus is kind of important. So working only with aperture isn’t always an option. A night cityscape, for example, which needs to be sharp throughout can be shot with a smaller aperture, lower ISO and lower shutter speed, you just need to use a tripod.  So the wider your aperture the faster your shutter speed can be because you are using more light but you’ll get a short depth of field. The narrower your aperture the slower your shutter speed but you’ll get more front to back sharpness.

Shutter speed

Shutter speed is, for my kind of photography, something I have to be constantly aware of. While a quickly shot portrait at a wedding can be acceptable whether using a short or long depth of field, a blurred image is next to useless. So I always try to keep my shutter speed at about 1/60th of a second or above. And I can manage this by adjusting the two previous components. With a combination of allowing more light in through the aperture and increasing my ISO a little I can get good usable images even in low light.

Example

Let’s take a look at the example below.

The trick then is not just to know how each of these elements work, it’s learning how they affect one another and how they can work together to get that perfect exposure. And sure, this takes practice. But next time you’re struggling to figure out why an image isn’t exposing correctly, an awareness of the elements of the exposure triangle might be useful.

The Exposure Triangle
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