Explaining Aperture & How It Works

What Is Aperture?

Aperture is one of the three pillars of photography (the other two being Shutter Speed and ISO), and certainly the most important in my opinion. In this article, I go through everything you need to know about aperture and how it works and how you can make it work for you.

Think of Aperture, or your F-Stop, as a circle (because it is) and at it’s lowest number (whether it’s 1.2, 1.4, 1.8, 2.0, 2.8, etc) it’s wide open like a big O and it’s highest number (whether it’s 14, 16, 18, 22, 32, etc) it’s closed nearly shut like a little o. The lower the number the more light that can come into your camera, giving you a brighter exposure. The higher the number you set your F-Stop at the harder it is for light to get in, which would force you to either adjust your ISO or Shutter Speed.

Still confused? If so, let me try again. Similar to the pupil in your eye, the aperture diaphragm opens and constricts to control the amount of light passing through the lens. To facilitate a properly exposed photograph, we need to quantify the size of the opening so that we can mathematically incorporate this opening into our calculation for exposure. Luckily, especially if you have my math skills, this has been done for us already.

Why Is Aperture Important?

The main reason you’d want to adjust your camera lens’s aperture is to take control of depth of field. Depth of field refers to the amount of the image that’s in focus – from front to back. A shallow depth of field means that only part of the image will be in focus. The rest of the image will be blurred.

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This is perfect for portrait photography where you need to draw attention to your subject. The shallow depth of field means your main subject is in sharp focus against an attractive, blurry background.

To get a shallow depth of field in your photos, you’ll need to use a large aperture – such as f/4. The further away your background is, the more likely it is to be blurry. This is useful to remember if your largest aperture isn’t large enough to blur the background a lot. Move your subject further away from the background and shoot again. The blur should become more noticeable.

A large depth of field means that all or most of the image will be in focus whether objects are near or far away. This is perfect for landscape photography where you want everything in sharp focus. To get a large depth of field you’ll need to use a small aperture, such as f/16.

How To Use Aperture?

The ratio of the opening of a lens aperture when compared to the size of the lens—not a measurement, but a ratio—is referred to as an f/number, f/stop, focal ratio, f/ratio, or relative aperture. Regardless of the term you use, aperture values are spaced, for mathematical purposes, in exposure values (EV) or stops.

Long Exposure

The benefit of mathematically figuring out EVs is that we can apply this measurement to all three adjustments that affect exposure—aperture, ISO, and shutter speed. With three adjustments all speaking the same “language,” we can use them simultaneously or independently as needed.

The formula used to assign a number to the lens opening is: f/stop = focal length / diameter of effective aperture (entrance pupil) of the lens.

Shallow Depth of Field

As I said at the top of the article, the smaller the number, the wider the opening. Therefore, a lens with a larger-diameter and optics will allow a larger opening represented by a smaller f/stop. Your lens/camera might allow you to “dial up” different numbers than what is shown above; older manual lenses usually “click” at 1/2 stop increments. These numbers, seen on a digital display, like f/3.3 for instance, represent 1/2-stop or 1/3-stop ratios.

Let’s Recap!

Beginner photographers may have trouble understanding aperture at first, because the bigger the number, the smaller the opening and vice versa. So, the backwards system works like this:

f/1.0 = really big opening
f/22 = really small opening

F-stop: the number that says how big the opening is

Stopping Down: Changing the aperture to let in less light. If you shrink the opening so half as much light gets through, you are stopping down (f/1 > f/1.4 > f/2…).

Full Stop Settings: 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

Aperture Ring: a rotating ring on the lens barrel that allows manual adjustment of f-stops

Fast Glass: wide maximum aperture lenses like f/2.8 or f/2 and wider

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