Exposure… demystified

You’ll hear a lot of talk about the exposure triangle or exposure pyramid, but it’s generally made far more complicated than it needs to be. If we break it down, it becomes much easier to work with.

Let’s start with ISO. Back in the days of film, ISO (International Standards Organization) or, as it was originally called, ASA (American Standards Association) referred to the speed of the film being used. The emulsion used on the celluloid substrate determined the film’s sensitivity to light, and the number used determined the “speed” of that film. When you set the film speed value on your camera, you were baselining the camera’s light meter to provide accurate readings. Of course, the entire roll of film had the same speed setting, unlike the digital world where we can change the setting per exposure if we choose.

Given that we’re no longer worried about film sensitivity, we’re now baselining the camera’s sensor and metering system by setting an ISO value.

Where the electronics in our current cameras are so sophisticated now, I simply go into the camera menu and set ISO to AUTO, and let the camera determine the appropriate value based on the lighting in the scene I’m shooting. There are some rare exceptions when you may prefer to set it yourself, but AUTO covers the majority of shooting scenarios, and will not let you down.

There. One third of the triangle done, nice and easy.

In terms of Aperture and Shutter Speed, what you’re shooting has a lot to do with which to prioritize. If you’re shooting sports, for example, then your shutter needs to be a priority in order to freeze the action and prevent blurred images. On the other hand, if you’re doing portraiture or scenics, prioritizing Aperture lets you control the depth of field, or how much will be in focus in front of or behind your subject. If I’m shooting a portrait, I’ll open my lens to a larger aperture so that my subject will be sharp with a soft, blurry background. That highlights the subject, almost giving it a three-dimensional look.

If I’m shooting a wide-open area, like a mountain range or a cove opening onto the ocean, I’ll stop my lens down to a smaller aperture in order to keep everything in the image sharp.

Why do the larger f stop numbers indicate smaller openings instead of the other way around? I have no idea, but it’s a quirk you get used to. I’d think it would make more sense the other way around, but… I didn’t make the rules.

At least, shutter speed numbers make sense. The higher the number, the faster the shutter will open and close to limit how much light actually gets to the sensor. A good rule of thumb to remember here is to use a shutter speed that is equal to or greater than the focal length of the lens you’re using when handholding the camera. Using a 50 mm? Shoot at no less than 1/60 of a second. Using that 105 mm portrait lens? Don’t shoot at less than 1/125 of a second. A simple rule, easy to remember and helps to minimize camera shake, which will blur the shot.

Keeping these simple, basic rules in mind will yield MUCH better images than leaving the camera in PROGRAM (or, as I call it, PHD/Push Here Dummy) mode and letting the camera do everything but press the shutter release, I guarantee it. As you get used to using them, they’ll become second nature, allowing you to concentrate on your composition and produce even BETTER images!

Is there more to it? Hell, yeah! But, let’s get comfy with this, let’s focus our attention on our compositions and capture what we want to see and go from there for the time being.

Published by Bob Vincent

Just me...

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