Aperture – Stepping Down to Open Up

Mike Selander

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This article was originally published in Issue 9 of EuroBerge and has been converted into a post on the site for your enjoyment. It was originally published on October 15th, 2010.

While the word ‘aperture’ has become a familiar term to those in the camera world and anyone holding a point-and-shoot in their hand, many don’t truly understand the depth and characteristics involved in the concept of aperture. Aperture is one of the most dynamic tools in photography when used properly.

The concept of aperture itself is a very simple one: There are circular leafs in every lens that open and close determining how much light is allowed to reach the camera sensor. The more open these leafs are, the more light is let in. From there, however, it gets much, much more complicated; a change in aperture also affects shutter speed, depth of field, and should even be taken into consideration for your next lens purchase.

Each aperture is assigned a value from f/1.0 all the way to f/128 (although most 35mm lenses only reach f/32). This value is determined by how open the leaf shutters on your lens are open. (Check out the photos on the following pages for an easy visual of this) A specific number, or f-stop measures this; at f/1, your lens is the most open, allowing the most light in and opposite for f/32 and up. Since the leaf is open more at a lower aperture, you can use a faster shutter speed to compensate as light enters in the camera body ingraining the image on film or digital sensor more quickly. Since they let the most light in, the lower apertures (generally 4 and below depending on the lens) are referred to as “fast” apertures.

This inverse relationship is known as exposure. Exposure is determined by what light conditions you’re shooting in.  The less light there is, the more and more you have to compensate with either your shutter speed or aperture. If you’re in low-light conditions, you generally have to use a slower shutter speed to compensate for the lack of light. However, this often leads to blurry images that don’t capture action. For example, if you are shooting motorsports at night, or the sun is quickly setting behind the hills, you will often want to keep a fast shutter speed in order to capture the action. To correct for this, push your aperture as low as possible, therefore allowing you to use a faster shutter speed. Likewise, if you’re in a condition with good light source, you need a larger (or less open) aperture if you want to maintain your shutter speed to compensate for the brightness. This is especially useful for rolling or panning shots.

Aperture also dictates a photo’s depth of field (DOF). DOF determines how much of your photo is in acceptable focus. The smaller the aperture, the less of your photo is in focus outside of your desired focal point. For example, a shot taken at f/1.8 will have a very, very small area of your photo in focus, and as you raise the aperture more and more (to a higher f-stop) the rest of the photo will come in focus until you hit about f/32 where almost the entire image will be in acceptable focus.  As you can see in the photos to the side, the smaller the aperture, the less is in focus and in many cases, the more artistic the photo. Smaller DOF is particularly useful for taking close-ups and isolating your subject from the background, making the subject “pop” more.  More open DOF is best when you want to incorporate the background and include it as a focal point of the photo.

When purchasing your next lens, aperture is a very important factor in the pricing and selecting your lens. Cheaper lenses will have less range on aperture; say f/5.6 to f/22 for a general walk-around. Typically, more expensive lenses will have a much better range, especially fixed-focal-length lenses. As you get up in focal length and down in aperture, you will see prices on lenses rise exponentially. For example, a the difference between a 70-200mm f/4 and 70-200mm f/2.8 is $1300 (over three times the cost of the f/4!) so keep this and desired speed needs in mind when looking to purchase your next lens.

Aperture is yet another factor that will make or break your photo. Use it isolate your subject, incorporate your background, or make better use of the light available. Whatever you do with it, just taking the knowledge of how to manipulate aperture with you will take you a step above the average bloke walking around with a camera.