The Exposure Triangle

The exposure triangle is made up of three different settings: aperture, shutter speed and ISO.

Using these three settings: aperture, shutter speed and auto modes your camera sets itself up to properly exposure your photo. Generally our new modern cameras get this setting right or at least close enough most of the time. That’s why you can shoot on auto, P, aperture or shutter speed mode and be pretty confident your image will be properly exposed.

But each of these three parameters have specific functions when it comes to your image. While each one tells the camera and the lens how much or how little light to let in these adjustments also control depth of field (how much will be in focus) and how much action will be stopped or blurred and how much noise (called grain when using film) will be introduced by the sensor when ISO is increased.

So this brings us back to manual mode. In manual mode nothing is being set by the camera. There should be no surprises when it comes to finding the proper exposure for each image.

We can start by manually setting the sensitivity of the sensor (ISO on digital cameras is the same concept as film speed called ASA on film cameras). For basic outdoor photography on a sunny day ISO 200 is a good start. If it gets cloudy then ISO 400 is still fine. If you’re shooting sports like hockey or baseball then perhaps you’ll want to set your ISO at 1600 or more. And, yes this will introduce senor noise which will show on the image but most RAW editors now have anti-noise controls. Modern anti-noise controls can smooth out ISO noise so much as to make it invisible.

Once the ISO is locked in the next setting is going to be either aperture or shutter speed.

If depth of field is most important to you (landscapes or portraits with or without flash) then the aperture is set next (Wide open at f/2 or so will result in a shallow depth of field while f/16 or so will result in a greater depth of field).

If stopping or allowing action is the most important aspect of your image (sports, bird photography, motor racing) then setting the shutter speed is where to start. Shutter speeds over 1/250th or a second up to 1/4000th or so stops all action. Shutter speeds from 1/125 to 1/30 can be hand held with normal lenses for ordinary shots. Anything 1/30th or less is going to need a tripod to eliminate camera shake and is only good for shooting images where there is no movement (unless you’re shooting a creative scene where blur is important).

The trick here is each setting affects the other settings and affects the overall exposure of your image. So how do you know when you’ve got the right exposure? This brings us to the topic of the light meter. There’s a light meters in most (in not all) modern cameras but there’s a reason to use an external light meter and that’s the next topic.