Continuing our earlier discussion on understanding exposure, we can now discuss what I vainly call “The Photologic Triangle.” There are three variables in every exposure that work together in concert to create the images that can arrest your vision and capture the human spirit: Aperture, Shutterspeed & ISO. For this leg of the race, let’s talk about Aperture.
Aperture is the ratio of how much light actually passes through the lens & hits the sensor/film. You know how your pupils dilate in different lighting? That’s the human eye’s aperture priority system. Your brain is telling your eyes to let more light in so it can see the scene better. In photography, aperture is conveyed with f-stops (i.e. f/#). It kind of looks like this:
To simplify this to its basest level: a smaller number means a larger opening and a larger number means a smaller opening. I couldn’t tell you the mathematical reasons for this (I’m right-brained), I just know it’s a ratio of some kind and that it works. You don’t need to know the difference between a full stop & a 1/3 stop… Just understand how aperture works!
Now, that’s what you should be asking yourself: “How does Aperture relate to shutterspeed & ISO, and what are the advantages/disadvantages to using a wider aperture versus a smaller one?” Good question, my apprentice…
First, let’s talk about how aperture relates to the rest of the Photologic Triangle. If you’re shooting in a mostly dim room, you might notice that you need a fairly slow shutterspeed to capture properly exposed photos. This can lead to blurry or unsharp photos, which is generally frowned upon in our community. Let’s look at some samples.
Just taken with whatever items were on my desk, you can see how stopping down aperture allowed us to get to a shutterspeed that we could make sharp photos with.
According to my camera’s metering system, these are both “technically correct” exposures. The photo on the left was shot at 1/2s, f/5.6 and ISO 100. It’s a little blurry right? The problem is that we need a faster shutterspeed to freeze the image in the frame; Aperture gives you a way to do that by allowing more light to hit the sensor (Technically, you could adjust any leg of the Photologic Triangle to allow create a “correct” exposure, but since we’re talking about aperture, let’s stick with it). If we open up the aperture from f/5.6 to, say, f/2.8, our camera tells us that a proper exposure can be made at 1/15s instead of the original 1/2s. Now, strictly speaking, neither of these are shutterspeeds that are safe to hand-hold (I’ll get to that when we discuss shutterspeed), and I cheated on the second shot by raising the ISO to 200. But if we shoot with these new settings, we get something like the photo on the right.
Now, there are a couple things going on here. Aperture affects something we photographers call “Depth of Field.” Notice how the background is a lot more blurry and the focus seems to fall off pretty steeply in front of and behind the subject? Wider apertures tend to create very shallow depth of field. There are other variables, too (i.e., telephoto lenses & focal lengths offer narrower Depth of Field than wider lenses/focal lengths). This is the first of many push-pull compromises you’ll be confronted with in the wide world of photography. Take a look at these samples:
Shot at f/5.6. Notice the wider depth of field.
Shot at f/2.8 and zoomed a little more. Notice how much more the focus in the background falls off.
The first one was shot at f/5.6, and while the background is out of focus, it’s not nearly so much so as the second shot at f/2.8. The working distance from the camera to the model was similar in these shots, but I zoomed in a bit more in shot #2. Still, it’s a good representation of how aperture impacts depth of field.
A couple last notes about Aperture… Every lens made by humans is going to be sharper when stopped down (personally, I find the sweetspot for most lenses to be between f/5.6 & f/8). Lenses come in two basic flavors: Fixed aperture and variable. The difference relates to zoom lenses; over the entire focal range of a lens, a fixed aperture remains constant, whereas a variable will change the maximum aperture based on your focal length. For instance, my Nikon 24-70 f/2.8 can have a maximum aperture of 2.8 at any focal distance from 24mm to 70mm. A 70-300 f/4-5.6 lens can have a maximum aperture of f/4 at 70mm, but at some point along the zoom range, the maximum aperture will fall to 5.6.
Fixed apertures are targeted at the pros, who often require wider apertures. Wider aperture lenses not only allow you to do many creative things with depth of field, but they also allow your autofocus to work faster. If you’ve ever heard the term “fast glass,” that’s what it means. When your camera is autofocusing, it uses the widest available aperture like (f/1.4 or f/2.8) to provide more light to the sensor, which essentially gives your camera more information with which to make a judgement call. By investing in pro glass like this, it enables photographers like me to catch a unique moment quickly, while it’s happening, rather than missing the shot entirely because we can’t focus fast enough. This is one of those small things that really makes all the difference in event photography, and that’s why Photologic Images only invests in the highest quality photographic equipment available.
With this primer, you should feel fairly informed about the basics of Aperture. I encourage you to get out there, throw your camera in aperture priority and get some practice! In the meantime, stay tuned for part 3 in the Photologic Tutorial series: Mastering Shutterspeed!
