A Look at Understanding Depth of Field

In last Friday’s post about landscape photography, How I Photograph Landscapes, I presented a series of guidelines on the “what” and “how” I  use when making landscape images. One of them was “Create the maximum depth-of-field,” which just happens to be the focus of today’s post.

Today’s Post by Joe Farace

“And the wide-angle (lens) meant poor depth of field.”—Peter Robinson, in his book Not Dark Yet.

Mr. Robinson is a respected UK-based writer of mystery novels but I’m sorry Peter, a wide angle lens means you’ll have more depth-of-field, not less. Novelists often get photography wrong. And don’t get me started on the sloppy way book designers handle widows and orphans* these days. It  seems that the more famous and best selling an author is, the less the publisher bothers to copy edit, fact check or even spell check them! Yet, Mr. Robinson, thanks his copy editor by name in the back of Not Dark Yet, an otherwise interesting thriller.

It’s About Depth-of-Field

If you’re new to the concept of depth-of-field, here are a few basics to keep in mind: When focusing any lens, even if the camera is doing it, on a specific subject, the subject matter on that plane of focus (at that distance) is critically sharp. Objects not on the same plane of focus are theoretically out of focus but in reality there is a range of acceptable sharpness. And that’s where depth-of-field comes into play.

How I made this photograph: I photographed this abandoned barn as post of my ongoing personal assignment. The camera I used was a Canon EOS Digital Rebel Xti that was converted for infrared capture by LifePixel using their Standard IR filter ( 720nm.) The lens was Tamron’s AF 11-18mm f/4.5-5.6 Di-II (at 11mm) with an Av exposure of 1/100 sec at f/16 and ISO 400. The choice of the aperture and focal length produces lots of depth-of-field and maybe just a bit of diffraction (see below.)

For example, at typical shooting distances, one-third of the area in front of the plane of critical focus and two-thirds behind it are theoretically in focus. This total area is called depth-of-field  which can vary depending on a lens’s focal length, the distance from the camera to the subject and the aperture that’s being used. Using a lens with a wider angle-of-view increases the apparent depth-of-field while using a longer focal length lens decreases it.

Depth-of-field is aperture dependent too. The old rule of thumb being that as the aperture size decreases, the depth-of-field increases and vice versa when aperture size increases, the depth-of-field decreases along with the total area of acceptable sharpness. Increasing a photograph’s depth-of-field also increases the apparent level of sharpness by including more objects in the scene that appear to be acceptably sharp.

My personal rule for landscape photography was to always use a small aperture to produce the greatest amount of depth-of-field. But not too small. Using really small apertures can produce diffraction. As a lens is stopped down, lens aberration control improves but the effects of diffraction increase. Patrick Hall describes diffraction this way, “something strange happens when light passes through a tiny hole such as a small camera aperture: it bends and interferes with itself. This interference is called diffraction.” Diffraction is not a lens aberration or a manufacturing defect: It is an unavoidable consequence of the physics of light.

Using smaller apertures also means using slower shutter speeds and you may have to use a tripod to keep your camera steady. although really good IBIS can help too. If you have time, please read my linked post Four Reasons to Use a Tripod. Working with a tripod also enforces a slower more deliberate approach to composing images, so a side benefit is that the composition of your image may improve too.