In thinking about exposure and the photographic triangle we often talk about the three elements that make up the photographic triangle. Simply put, they are; aperture, shutter speed, and ISO.

But what exactly are aperture, shutter speed, and ISO? Here’s a quick rundown of these common terms of photography.

Aperture

Every SLR and DSLR (and many higher end compact cameras, range cameras, etc…there are plenty I promise) will allow you to manually and semi-automatically control the aperture or f-stop. Those are the numbers (5.6, 8, 11…) preceded by an f and a /. Looks like f/5.6, f/8, f/11…you get the idea. You’ve seen these numbers before, but what exactly do they mean?

These numbers correspond to a specific opening in your lens. This function allows the lens to control the amount of light that reaches the film or camera sensor. It can get a little tricky because the smaller the f-stop, the larger the opening. The larger the f-stop the smaller the opening.

Technically speaking the f-stop is a fraction that indicates the diameter of the aperture. So you have the focal length (that’s the “f”) divided by (/) the stop in use (the number). An 85mm lens set to f/2.8 would actually have a diameter opening of 30.36mm. Don’t worry, you really don’t need this information nowadays, it’s just kinda handy to know.

Here’s what you do need to know. Each time you descend from one aperture to the next it’s called stopping down. What this does is actually cut the volume of light coming into the camera in half. So f/5.6 lets in half the light of f/4.

This obviously works the other way as well. When you open the lens a stop up you increase the amount of light hitting the sensor or film by a factor of 2 (doubling the light). This happens when you move a full stop, but beware that many of today’s cameras allow you to control aperture in one-third stops. So knowing which f-stops are full stops is very important. I’ll list them below. Memorize them.

f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64, f/90, f/128

Shutter Speed

As the name suggests, this is about speed. The shutter speed controls the amount of time that the volume of light coming through the lens hits your sensor or film. Shutter speeds are typically represented by 1/250, 1/500, 1/1000 or sometimes just represented by the number 250, 500, 1000.

It’s better to think of it as 1/250 because we’re talking about fractions of a second. A shutter speed of 1/250 or 250 is literally 1/250 of a second.

Here’s what you need to know. Similar to aperture, shifting the shutter speed from 1/250 to 1/500 is a decrease of the amount of time that the volume of light hits the sensor for one full stop. Be aware that many of today’s cameras allow you to adjust in one-third stops here as well so knowing which ones are full stops becomes important again. Here they are.

1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000, and faster as technology advances.

ISO

ISO is a very complicated process of determining the light sensitivity of the film or camera sensor. Because of the variances in both film and processors it’s important to become very familiar with the way that your digital camera or film of choice handles the light.

In film higher ISOs produce grain and in digital photography higher ISOs produce digital noise or just noise for short.

If you want a technical breakdown of ISO in photography I refer you to the wikipedia page on film speed. You’ll learn how much anomaly there is between film manufacturers and camera manufacturers. Because technology is pushing the ISO higher and higher with each new influx of cameras it’s important for you to test and review how high you can push your camera’s ISO before you start getting too much noise. Example, I still shoot with a Canon 30D and rarely hit ISO 800 unless I absolutely have to and I know that those images are not for public sale and or consumption. Some of today’s cameras can comfortably hit an ISO of 1600 with tremendously great results!

Here’s what you need to know. Just as in aperture and shutter speed ISOs can be moved in light sensitivity by full stop equivalents. Going from an ISO of 200 to 400 doubles your light sensitivity one full stop. Be aware that many of today’s digital cameras and many of yesteryear’s and current film come in one-third stops so it’s important to know which ISOs are full stops.

50, 100, 200, 400, 800, 1600, 3200, 6400 and they’ll probably keep going up as technology progresses.

There you go. Aperture, shutter speed, and ISO in a nutshell.

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