The Exposure Triangle is the first (and main) step in mastering the dreaded Manual mode of the interchangeable lens camera mode dial.
There are three interrelated principles I need to know. And while each one is different, they all have the same overall effect. All 3 control how much light enters the scene. Thus they’re known as the Exposure Triangle.
Blink your eye rapidly. With that, we’ve just demonstrated how shutter speed works. The camera shutter is like my eyelid. And if I take a quick blink, I only allow a small amount of light to enter my eye. But if I take a slow blink, more light enters.
Shutter speed can thus be described as slow or long when the shutter opens and closes slowly. Or I can say I’m using a fast or short shutter speed when it blinks open more quickly. It’s described as fractions. 1/1000ths of a second is fairly fast while 1/15ths of a second is quite slow.
Shutter speed’s secondary function has to do with motion in photographs. If I want to freeze fast action, I need to use a faster shutter speed. Otherwise, the subject will appear blurry as it kept moving during the time frame the shutter blinked and the sensor recorded the change in position.
Notice the difference in these two photos. In the first one, the shutter speed is fast enough to freeze the motion of the subway train and the people aboard. But in the second, the entire train is blurred because we used a much slower shutter speed.
We can best understand aperture by squinting or opening your eyes wide. If it’s bright out and I want to reduce the amount of light hitting my pupil, I squint. And if it’s dim, I need to open my eye wide. My camera’s aperture setting is doing the same thing, only it’s adjusting how wide or narrow the hole that lets light into the lens is.
Aperture also has a secondary function; it controls depth of field. Depth of field is how much of a scene is in sharp focus. In the below scene the image has a very narrow depth of field. Notice how all portions of the piano are completely out of focus while the single flower bud remains sharp. This is using a low aperture number, such as f/1.4. We’ll discuss aperture numbers a bit later.
If I decided I wanted the entire piano in sharp focus, I’d have to use a larger aperture number, such as f/8 or more. Notice below how the aperture hole is much smaller than before. This would also give me a wider depth of field.
ISO or light sensitivity
ISO can best be thought of as how light sensitive my digital camera’s sensor (or film camera’s film) is. And using our eye example, it’s how overall sensitive my eyes are to light. Sensitive eyes can be said to be using a higher ISO number as it doesn’t take much light for them to work properly. And too much light makes them water, making me squint or blink rapidly.
Stops of light
Light stops are a photography term that can sometimes cause confusion. But fortunately, they’re actually pretty simple to understand. Each stop of light represents a doubling or halving of the amount of light striking the sensor. To make it easier to understand, let’s take each element of the Exposure Triangle separately.
ISO is the most intuitive. Each doubling of ISO represents me doubling the sensitivity of my camera’s sensor. Thus, ISO 50 is half as light sensitive as ISO 100. And ISO 200 is twice as sensitive as ISO 100 or four times as sensitive as ISO 50.
Using shutter speed, if I go from 1/60th of a second to 1/125ths of a second, I’ve halved the amount of light entering the camera, and vice versa. This is because the camera blinks twice as fast as it did before.
Aperture is the least intuitive as photographers don’t always use whole numbers Going from f/1.4 to f/2 represents a halving of the amount of light entering the camera. And going from f/5.6 to f/4 is a doubling. Remember the smaller the number, the wider the opening becomes.
The Exposure Triangle is the very first step in moving away from the Auto mode with a camera. Understanding how each of these three elements works and the interplay between them is what makes decent photographers good. So spend time in M mode playing with these three elements and see what you can create!