Today’s Question: How much should I stop down my lens aperture if I want to achieve optimal depth of field when photographing with a long lens from a long distance from a landscape?
Tim’s Quick Answer: When photographing a scene from a considerable distance, you might be surprised at how much depth of field you can achieve even if you don’t stop the lens aperture down much (or at all). When focusing at a distance of about one-quarter of a mile with a 200mm lens, for example, stopping down to f/8 will provide a depth of field that covers the full scene all the way to infinity.
More Detail: This was a question asked by a workshop participant while we were atop Steptoe Butte in the Palouse region of eastern Washington State. That means we were about one thousand feet above the surrounding terrain. Even assuming you are focusing on a portion of the scene relatively close to the base of the butte, your focus point would still be about one-quarter of a mile or so. If you were using a 200mm focal length, at f/8 you could have everything from about 500 yards to infinity in focus.
I think many photographers who have experience with landscape photography tend to think it is always necessary to stop down to f/16 or f/22 to achieve any significant depth of field for a scene. When using a lens with a longer focal length, of course depth of field becomes a more significant concern. But when you are focusing at a considerable distance, you will have greater depth of field. I often find photographers are surprised at just how much depth of field they will achieve when focusing from far away, even with a long lens.
When you combine a distant focus point with a longer lens that will be capturing a relatively narrow field of view, there’s a good chance that even with a relatively shallow depth of field you will still be able to have the full scene in focus. For example, even a 500mm lens focusing at a distance of about one-quarter mile will provide a depth of field that is about 500 feet deep. That may very well provide adequate depth of field for the full scene, considering the narrow field of view with a 500mm lens.
When focusing close, such as with macro photography, getting enough depth of field can be a challenge. But when focusing from a considerable distance, you may be surprised at just how much depth of field you can achieve, even without stopping down the lens significantly.