Open Wide and Say "Aah!"
Of all the controls that can influence how a photograph will come out, aperture surely ranks near the top of the list. A small aperture can create images with vast depth of field. A wide open aperture can yield something else entirely.
As a measure of how big the opening is through which light enters the camera, aperture clearly has an impact on exposure. Light easily gets through when the shutter is held open with a wide aperture. Make the hole smaller and a far less light can make it through in the same amount of time. The image will come out too dark unless you compensate with a longer exposure time or a higher ISO sensitivity.
At the same time, changing the aperture also affects the depth of field. This is often viewed as a good thing when stopping down to a smaller aperture gives us greater depth of field. It's often viewed negatively when opening up to a wider aperture decreases the depth of field to a point where not everything can be held in focus. Many photographers will complain about this as a problem and do their best to avoid it.
But a shallow depth of field doesn't have to be a curse. It can indeed be a blessing when used creatively. Aspiring photographers are often advised to get closer to simplify their compositions and make clear what their subject is. But another way to simplify is to render everything out of focus intentionally with a wide aperture, leaving only the essential essence of your composition clearly defined.
Sometimes this can be a helpful strategy for getting to the heart of what interests you in a scene. Other times it can be a lifesaver, allowing you to create an image when no other strategy will.
This first shot was taken in the Palouse region of Eastern Washington State, spilling over into Western Idaho. It's a magnificent area for photographers. The rolling hillsides create an endless variety of forms and graphic shapes that almost beg to be photographed. Every spring when the crops are at their peak and again in the fall at harvest time, photographers from the Northwest and far beyond are drawn to the mazes of country farm roads that provide access to the sights. Abstract, graphic compositions and old barns create amazing possibilities.
But in addition photographing to the beautifully sumptuous curves and endless, textured vistas of color, it can be rewarding to look for ways to simplify the experience, distilling it down to just the essence. One of the best ways to do this is by opening up your lens aperture such that only a narrow slice of those vistas remains in focus. The trick of course is to carefully choose that slice. Just as with macro photography, attention to detail is called for to get the best shots.
I took this shot from the side of the road, not because I was lazy, but because it was the only place where the otherwise endless fields have a defined edge. The lens used was a long telephoto with an extension tube so that I could focus more closely. Still, I needed a good fifteen to twenty feet of open space between me and the foreground grasses where nothing would intrude into the frame. I didn't want blurred grasses. I wanted a clean shot of the grasses that are in focus here with nothing intervening. Additionally, the camera is pointed up just enough to avoid seeing most of the grasses beyond this clean edge. The background is cleanly divided into equal areas of blue sky and yellow from a distant field of canola in bloom. I really liked the smooth, contrasting yellow and blue areas, and without such a wide open aperture, too much detail would have shown on that yellow hillside. I chose to shoot wide open to capture what I wanted.
This second shot was taken at last light, in a drainage ditch along the side of a state highway. I was driving east towards the mountains. The setting sun in the west was casting a beautiful pink glow on the mountains, and the full moon was starting to rising in the distance. My girlfriend at the time was sitting beside me in the car and thought it would make a nice image. After trying to make the case that, while the scene had potential as a background but there really wasn't much in the way of a foreground, I relented and pulled over. The exposure for anything at ground level where it was already quite dark was so different than for the sky where at least some light remained that I struggled to find a composition that would work.
In the end, what I found was the silhouette of weeds growing in the drainage ditch alongside the road. Thankfully, you can't tell that from the resulting image. What you can see is the completely featureless disc of the moon rising over a mysterious pink glow in the middle of the frame. That glow came from the last light of sunset reflecting back into the lens off the mountains in front of us. The foreground grasses anchor the image and provide at least some context by defining ground level.
I had to use the widest aperture I could to get a useful image. While I could have gotten the same exposure by stopping down and leaving the shutter open longer, the weed stalks wouldn't have cooperated. I needed a fast shutter speed to stop them from swaying in the wind which meant I needed a wide open aperture to get any kind of exposure recorded at all. The resulting shot was therefore born in large measure out of simple necessity. Nothing else would have worked. But I rather like the way it came out.
Regardless of whether you open your aperture wide out of necessity or purely by choice, the results can be quite rewarding and pleasurable.
So open up, and say "aah!"