The focal length of the lens you use, combined with the aperture setting, determines how the camera sees whatever you point it at. This has profound implications for composition. Let’s look at them one by one.
Selective focus and bokeh
Selective focus occurs when you focus on your subject, and use a wide aperture to make the background go out of focus. Bokeh is the blurred parts of your photo. It originates from the Japanese word boke, and has come into use because we don’t have a word in English for it.
There are several factors that affect bokeh.
The wider the aperture, the less depth-of-field there is, and the more bokeh you get. Photographers that like to use selective focus buy prime lenses, as they have often wider maximum aperture settings than zooms.
But, you can still obtain nice bokeh with zooms, if you pay attention to the following points.
2. Camera to subject distance
The closer you are to the subject the less depth-of-field there is. This is a useful tip if you have a zoom lens with a limited maximum aperture (such as an 18-55mm f/3.5-5.6 kit lens). Just set the focal length to longest available setting, the aperture to its widest setting, and move in as close as you can. You’ll be surprised by what you can achieve.
3. Subject to background distance
The more distance there is between subject and background, the more out of focus the background will get, at any given aperture setting.
4. Quality of light
Light affects bokeh. Soft light (like that on an overcast day) produces smooth, even bokeh. Sunlight or reflections, create a different type of bokeh with more texture.
5. The aperture blades of the lens
The more blades the lens has, the rounder the shape of the aperture, and the smoother the quality of the bokeh. Less expensive lenses tend to have fewer aperture blades, and may not produce the same quality of bokeh as better ones.
6. Other optical characteristics of the lens
Some lenses, such as the Helios 58mm f/2 lens, used to take the photo below, have optical characteristics (or more likely, flaws) that produce a certain type of bokeh. Lensbaby is a company that makes lenses that produce a specific type of bokeh.
f/2.8 on a prime lens
I’ve singled this aperture setting out because it hits a sweet spot when it comes to composition, especially for portraits.
If you have a normal or short telephoto prime lens, and use the widest aperture setting (generally f/1.2, f/1.4 or f/1.8) then the depth-of-field is very narrow indeed. Sometimes that works really well, but other times you need a little more depth-of-field to create a stronger image. It’s like any technique – overuse it and it becomes a gimmick.
The solution is to mix it up a little by using aperture settings like f/2, f/2.8, and f/4. You’ll still get a narrow depth-of-field and create some beautiful bokeh, but a little more of your subject will be in focus.
Using f/2.8 (or thereabouts) shows subtlety, restraint, and maturity.
The middle apertures
Now we get into the middling apertures, those from around f/4 or f/5.6, to f/8, depending on your lens.
The effect of these apertures depends on the focal length of your lens and how close you are to your subject. For example, you could use a super telephoto lens (300mm plus) and shoot from farther away from your subject to create images with shallow depth-of-field at f/5.6, or get the entire scene in focus at the same aperture with a wide-angle lens (35mm and less) if you focus on the right spot and are much closer to your subject.
These middle apertures represent the transition between photos where some of the image is out of focus, to those where everything is in focus.
You can still use selective focus at these apertures (although perhaps not with wide-angles), although the effect is much gentler than with the widest aperture settings of your lens. Use these apertures when you want good depth-of-field but don’t mind if the background is out of focus a little.
The smaller apertures
These are the ones you use when you need everything within the frame to be sharp, like with landscape photography. This can be anything from f/8 on a wide-angle lens, to f/11 or f/16 on longer focal lengths. With telephotos and macro lenses you can stop down to f/16 and still not get everything in focus.
The thing you need to be aware of here is diffraction. When the aperture gets too small, the light passing through it spreads out, and softens the image. Thanks to diffraction, images taken at f/22 are usually visibly softer overall, than those taken at f/8 or f/11. Noticeable diffraction may start at f/16 or f/22 on a full-frame camera, and around f/11 on an APS-C camera.
Every time you take a photo you should be thinking about what the optimum aperture is for the composition you want to make. Do you want to open the aperture and throw the background out of focus? Do you want to stop down and get as much as possible in focus? Or somewhere in between?
What aperture settings do you like to use with your photos? Do you use a Lensbaby or other lens that gives a certain bokeh effect? Please let us know in the comments – I’d love to hear your thoughts and see your images.
This week on dPS we’re featuring a series of articles about composition. Many different elements and ways to compose images for more impact. Check out the ones we’ve done so far:
- Using Framing for More Effective Compositions
- 7 Tips to Improve Your Skyline Photos
- 33 Images that Exemplify Compositional Elements
- Weekly Photography Challenge – Composition Craziness
My new ebook Mastering Composition will help you learn to see and compose photos better. It takes you on a journey beyond the rule of thirds, exploring the principles of composition you need to understand in order to make beautiful imag
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