Giving your images a distinctive and interesting look is always a challenge but there are several tools available. Depth of field is a popular “art” tool that enables you to quickly bring the viewer’s eye to the exact subject you want them to pay attention to right from the start. To use effectively, though, you need to understand what is the depth of field you’re going to get for your composition? It’s a tricky question – each lens behaves differently based on aperture, distance from subject, focal length, etc. You almost have to experiment with your bag of lenses and learn. Or you can look up the depth of field chart for your lens and memorize it. My problem with the latter option is I have a hard time visualizing what a 3 inch depth of field or a 500 foot depth of field looks like. I usually just play around with my lenses and see what they deliver.
It’s especially daunting with telephoto lenses. The depth of field for these starts out short and seems to only get smaller. Here’s an example:
I liked the little snowball sitting in the sunlight so I wanted to make an image of it. I was sitting at a picnic table with my camera on my tripod, using my 300mm manual focus Olympus lens (from the OM film camera days). On my digital Olympus body this is equivalent to a 600mm lens on a full format camera. I’m about 10 yards from the snowball so this long lens really gets up close. I think the aperture was around f/11 or f/16 since I was looking for maximum sharpness. Notice the area that’s in focus – it’s a narrow band where the snowball is in the sunlight. The grass in the foreground and snowbank in the background are completely out of focus. Which is what I wanted – you eye should go right to the snowball. But how much depth of field is really there?
If I zoom in on the image you can see the depth of field is REALLY narrow; according to one online DOF calculator it comes in at 4 inches. Which means if I was making an image of a deer’s face using this distance and settings, their eyes would be in focus but their ears and nose might not be – and this is at a small aperture (not that I expect to be 10 yards from our local deer, at least not unless I’m holding a handful of corn for them). It does give a cool look, though, as it centers your eye right on the subject I want you to pay attention to. Like most specialized tools – and a long telephoto lens is definitely that – you get the best results when know the lens’ limitations and operating within them.
In my youth as a photographer I was always trying to get maximum depth of field, especially with landscapes. I’ve learned now that shortening it up can truly bring some interesting features to your pictures. Just have to know when and how to use the technique effectively and what tools work best to deliver on it.