Mastering Aperture in Photography: Capture Stunning Light and Depth

After you have composed your shot (take a look at the post on Composition), the next consideration is exposure. Exposure refers to the amount of light that reaches the camera’s sensor, and it’s governed, camera-wise, by three settings: Shutter speed, ISO, and aperture. I’ll go into all of them in their time, but I’ve just completed a photography lesson on Aperture, and I wanted to experiment with it a bit to really get a feel for what it can do to and for a photo. The environmental light is also a factor in your final image, but we can, to a certain extent, compensate for that with our Exposure Triangle, as we call it.

An aperture is an opening of any kind, so in photography, aperture, as opposed to “an” aperture”, refers to the size of the opening that lets light in to get to the sensor. Digital SLRs and Mirrorless cameras, and some higher-end Point-and-Shoot cameras (such as the Canon Powershot Sx-60) have the ability to control aperture settings. In the film world, Single Lens Reflex (SLR) cameras also have the ability to control aperture, but the analog versions of Point and Shoot cameras do not. In the digital Point-and-Shoot cameras, those settings are governed digitally, but there isn’t anything in a film Point-and-Shoot (called Rangefinder cameras) that allows the operator to change that setting.

HOW DOES APERTURE AFFECT YOUR PHOTO?

First, aperture affects the exposure of the image – how dark or light, to put it very basically. Aperture affects the amount of light that is let in during the time the shutter is open. Later in this series, I’ll describe how shutter speed affects the length of time the shutter is open letting light in, and also how the ISO, the sensitivity level, accepts the light that is let in. When the aperture is wide open, lots of light comes in, when it’s very narrow, very little light gets in.

Aperture also affects how much of the stuff you’re pointing the camera at is in sharp focus. Aperture is a strange thing, when you have your aperture set really wide, you end up with a really shallow depth of field, which is the amount of the scene in sharp focus. This is why, when you look at a portrait that was taken with a busy background, the face is in focus, but the background is blurred, very much out-of-focus. A very small aperture will create a scene in which more of the image is focused, from the peaks of the mountains in the distance to the daisies at the very forefront of the scene. Wide = shallow depth of field, narrow = deep depth of field.

LET’S GET REALLY CONFUSED NOW

The increments of the aperture options are measured in f-stops, and that’s worth another blog post in itself, and I’ll address that when I get to it in my course.  What you need to know about f-stops is that smaller f-stop numbers correspond to larger aperture settings and larger f-stop numbers correspond to smaller aperture settings. While it is also true that the larger f-stop numbers, corresponding to a smaller aperture setting, also correspond to a deeper depth of field, and that the smaller f-stop numbers, corresponding to a larger aperture setting, also correspond to a shallower depth of field, you’re usually only going to be concerned either the amount of light hitting the sensor or the depth of field for focus. When you need to consider both, you’ll want to focus on the depth of field and use the other exposure elements for light control.

EXAMPLES FOR EXPOSURE

I took some images of the exact same object from the exact same position, changing only the aperture setting. As you look through them, you’ll see that as I opened up the aperture, more light came in and we were able to see more of the object.

The first image was taken at full automatic, and the camera selected the settings. The camera’s settings were 1/5 of a second, f/7.1, ISO 1600.

I took the camera to complete manual, and I set the ISO to 6400 (if I wanted to really get a shot here, I’d increase the ISO), with a 1/125 of a second shutter speed, then I tightened the aperture way down as far as it would go with this lens and camera, f/36. We can’t see anything, but I would actually be able to manually expose it in Lightroom.

I took several more shots, stepping down a bit each time, and we don’t really see any change until we reach f/14, and we can really only barely see something.

From here on out, each step down provides a little more clarity on the image:

f/11.0

F/8.0

F/7.1

We finally got to a point where, at the same settings for ISO and shutter speed, it was as good as it was going to get.

EXAMPLES FOR DEPTH OF FIELD

Depth of field can be explained as how deep the field of focus is, that’s how you can remember what it means. Remember that while the f-stop number corresponds inversely with the amount of light hitting the sensor, it corresponds directly with how deep the field of focus is. When we want the sharp focus only on our primary subject, we’re going to use a very shallow depth of field (lower f-stop number), but when we want everything in focus, like a magnificent landscape, we’re going to use a wide depth of field (higher f-stop number).

The image below shows a very shallow depth of field. The hummingbird and the feeder are in sharp focus, but all of the background is decidedly out of focus. This photo was shot at 1/400 of a second, at a pretty low ISO because it was broad daylight, and the f-stop was set to 4.3, pretty narrow.

The next image has a wide depth of field, because it’s a landscape and I don’t want anything to be missed. I want the foreground (the area closest to me), the midground (the middle of the image), and the background (the top of the trees in the distance) all to be in focus, so I chose a higher f-stop of 20.0. Once again it was daylight, so the ISO is 640, and the shutter was open for 1/200 of a second.

As we move through our experiments, I’ll show you how you can use the other members of the Exposure Triangle to compensate for Aperture adjustments, so you can get the focus on the part of the picture where you want it and still get the level of exposure you’re looking for.

HAS THIS BEEN HELPFUL?

Let me know if there’s something I can clarify for you, or if you’d like an explanation on a different aspect of learning photography.

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