Using Depth of Field

Apr 15, 2011 by Vaccinium

Using Depth of Field

So, how do you know what is and what isn’t in focus before you take the photo? Ideally, your camera will have a Depth of field (DOF) preview button, when depressed, will show you through your viewfinder exactly what the photo will look like in terms of depth of field. Higher priced cameras have this option, but even then, it is far from perfect, as you are looking at a tiny image, and the image is very dark when the camera is stopped down ( going towards a smaller aperture/larger f-stop) pretty far. Another way of determining what the depth of field will be is of you have a lens with a DOF scale, which is a set of markings on a lens which permits you to estimate where the image will be acceptably in focus based on knowing the distance away from your subject and the aperture. Unfortunately, modern point-and-shoot cameras and even many modern SLR lenses lack these markings. You can even print out charts that take into effect the specific lens multiplier factor of your lens, distances, apertures, and focal lengths to figure out quite specifically where an image will be acceptably in focus.

Confused? Frustrated? You know what, I am too. Frankly, I don’t use any of these for my photography. I occasionally use my DOF preview button, but only up to, say, f/8. Any f-stop higher than that will be so difficult for me to see that it’s not worth my trouble. Instead, I use my best judgment based on my experience to choose what I feel is going to be the best aperture/f-stop to obtain the desired DOF for the photo I’m taking. After I take the photo, I look at the image on my camera’s LCD screen and judge how I did. Usually I get it right the first time, but if not I’ll retake the photo with a different aperture. I just don’t like the idea of peering into a dark viewfinder or consulting charts every time I need to take a photo. After all, photography is supposed to be fun, right? To be truthful, using DOF charts and a lens with a DOF scale will definitely help, and for certain types of technical photography it is an absolute must. However, getting the “wrong” aperture by a stop or so in recreational photography isn’t a big deal.

It will take time for you to become comfortable with your camera and lenses to get a good feel for how to master DOF. It takes patience and it takes attention to details, but it is so worth it. A good exercise is to take your camera somewhere and take several photos of a subject at different apertures, focal lengths, and shooting distances and look at them on your computer when you get home. Take notes on your shooting distance and focal lengths for each shot (the aperture and shutter speed should be available on your camera) and then compare them to the resulting images on the computer. Once you understand what a photo is likely to look like under various settings, you’ll be well on your way to choosing the right apertures for the photos you’ll be taking in the future.

You might think that having a large aperture (small f-stop) would never be desired because so little of the photo would appear to be in focus. It is true that that for many photos, having too much of the photo out of focus would detract from the beauty of the photo, but for many other photos, having a shallow depth of field is precisely what is called for.

Shallow depth of field helps the subject of your photo “pop out” from the rest of its surroundings. For example, a raindrop on a leaf stands out with shallow depth of field (Figure 1), whereas with a small aperture (large f-stop) would make that raindrop blend into the background (Figure 2). Look at the last professional portrait you had done of yourself. Undoubtedly, that photographer did something similar, with your face in focus and the background more blurry.

Extremely shallow depth of field produces a lot of highly desired “bokeh” around the subject (Figure 3). Bokeh is the dreamy, out-of-focus areas found near the in-focus portion of your subject, and, for whatever reason, human eyes find this effect quite appealing. This is different from out-of-focus areas in the foreground or background, which mostly serve to focus your eyes on the subject. Bokeh, on the other hand, is part of the subject.

In general, whatever is in focus is going to draw the eye of someone looking at a photograph. When the subject of that photograph is something small and discrete like a flower or a face, shallow depth of field can be helpful to focus your attention on it. However, shallow depth of field may not be preferable if you want to photograph a scene where there are multiple subjects to which you want to draw the viewer’s eyes. This is the reason why the vast majority of landscape photographs are sharp and in focus to our eyes at every point in the photo (Figure 4).

As an exercise, the next time you are out (or in) taking photos, visualize the image you want to take using what you just learned about depth of field. Do you want a lot of the photo to be in focus? Do you want very little of it to be in focus? Whatever you decide is best, set yourself up and take that photo. After you’ve looked at it in the viewfinder, and deemed it acceptable, pause for a moment. Before moving on to another subject to photograph, try to imagine how you could take another photograph that is completely opposite the one you just took in terms of depth of field. For example, if you just photographed a rusty, junked car outside a dilapidated barn and decided that you wanted to have both the car and barn in focus, you would have selected a small aperture (large f-stop). However, there is always another way to look at the scene. Maybe you could move your camera a few feet and focus on a headlight and grill of the car with a large aperture (small f-stop), with the barn still in the background. That would give you a photo with the headlight and grill as the subject of your photo, but the barn would still be in the background as a fairly recognizable, complementary feature. Take your time and imagine all the possibilities of working with different depths of field – you’ll become a better photographer because of it.

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