I tend to think that aperture is one of the most neglected tools by beginner digital photographers. Professionals and hobbyist swear by it, but their enthusiasm hasn’t necessarily carried over to the snapshot crowd.

Maybe this is because aperture isn’t necessarily as intuitive as shutter speed. Everyone understands what 1/800s means, but it’s harder to quantify exactly what f/2.8 means. Then there’s the whole business with larger f/numbers equating to smaller apertures…it’s just a mess.

But if you are a beginner, don’t let that scare you away. Aperture is a great tool for making a statement in your images. Here’s an introduction to a range I’ve dubbed “isolation apertures” that will help your images say more.

Image originally uploaded by vonvonvon.

Just so we’re on the same page, here’s your two-sentence summation of what aperture is: Aperture is a measurement of the diameter of the opening in the lens admitting light to the sensor. Small apertures are connoted by large f/numbers and produce a wider depth-of-field, while larger apertures have a smaller f-number and produce a greater depth-of-field.

Got it? Good. Thematic apertures are the larger apertures on digital cameras - those between f/1.4 and f/5-ish, generally, but the range can get a little bigger depending on the length of the lens. These apertures produce a very small depth of field, which gives you the potential for very exacting control over what your image says.

The natural tendency for a lot of beginning photographers is to leave the camera in full-automatic mode. There’s nothing wrong with this, but the camera’s meter is generally not going to choose an aperture in the isolation range unless lighting conditions are very dim. By moving out of automatic mode and into aperture-priority mode, you can wrest control away from your camera and choose apertures on your own.

What’s the advantage in this? Small apertures allow you to pick-and-choose exactly what’s in focus in the image. This can produce some stunning effects. Take a look at these two pictures and think about how the impact would change with a wider depth-of-field and a larger aperture:

worker hands, originally uploaded by Tatiana Cardeal.

Coruja-buraqueira, Coruja-martelo, Coruja-do-campo (Speotyto cunicularia) 2 25-03-07 149 - 9, originally uploaded by Flávio Cruvinel Brandão.

Both photos used an isolation aperture for a different purpose:

• - The first photo uses isolation aperture to make a statement. The title of the shot is “Worker Hands” and that’s exactly what the large aperture keeps the focus on. While I suspect the photo would still look good with a smaller aperture and a broader depth-of-field, it would have lost the message the photographer was trying to convey.
• - The second photo of the owl uses an isolation aperture to remove unwanted detail. Think how distracting that tree branch would be if the image had corner-to-corner sharpness - it would appear to be coming right out of the bird’s head! But by using a smaller f/number, the branch becomes less noticeable.

Those two photos are indicative of the main reasons a photographer would choose an isolation aperture - controlling message and removing unwanted detail. Neither would have been possible unless the photographer had taken aperture into their own hands.

Isolation apertures are popular in many different genres of photography:

• Portrait photography: Used to isolate the subject from the background, keeping the focus on the person.
• Macro photography: Again, used to isolate against a backdrop and to call attention to fine detail.
• Photojournalism: Used to control the message of an image.

Now, less I get jumped on, aperture is not the only determinate of depth-of-field. Lens length plays a role - as the lens lengthens into telephoto range, smaller and smaller apertures can be used while still getting an isolation effect. Distance matters, too. The closer the photographer gets to their subject, the greater the potential for isolation. This is why macro lenses are in such demand - the combination of a long lens and a short minimum focusing distance allow the photographer the greatest control over the depth-of-field in an image.

Keeping in mind those factors, it’s still fair to argue that aperture will have the greatest relevance to the average photographer seeking to control the depth-of-field within a frame. Next time you’re out shooting, spend some time thinking about how an isolation aperture could change what your photo says. There’s the potential for some great shots that are missed if the camera stays set to automatic mode.

Quick note: Sharp-eyed readers may notice that I originally was going to call this article “Storyteller Apertures”. I was tipped off that Bryan Peterson uses this term differently in his excellent book, Understanding Exposure, so I went ahead and changed my terminology out of deference. I’ll explore Peterson’s storyteller aperture soon.

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