Focal Length, Distance to Subject, and Depth of Field


This was shot with an 85mm lens, 8.7 feet from the subject, at an aperture of f/2.5. I love the lighting, expression, and creamy bokeh of this image, but I felt that the Indian figurines on the mantle were TOO blurry to be recognized. I hoped to make another version of this image with slightly greater depth of field. Because I was close to Frank with a long lens, the figurines appear much closer to him than they do in third photo below.

Reviewing images from a rehearsal of the Ojai Art Center Theater’s production of And Then There Were None, I noticed three images that illustrate why we often end up with too much or too little depth of field in our photographs.  Depth of field, as you know, refers to the range of apparent focus from foreground to background.

The  images in this post were taken with different lenses at different times and from different distances. Two of the lenses were set to an aperture of f/2.8, while the third was set to f/2.5. This is not a scientific test, as the images have been cropped, and were taken from different angles under different lighting, but they still show us an important fact about depth of field. You see, every aspiring photographer knows that smaller apertures (e.g. f/16) produce greater depth of field and larger apertures (e.g. f/1.4) produce very shallow depth of field. But other factors influence the area and character of apparent focus, including focal length, sensor size, distance to subject, and distance from subject to foreground or background. It’s actually kind of complicated, and that’s why, unless I’m in the studio or really taking my time to set up a shot, I rarely get precisely the depth of field I would like.

This was shot with a 105mm lens, from a distance of 12 feet, at an aperture of f/2.8. The focus point was on Frank's eye. Note that the wallpaper is not sharp, but it's clear enough to be distracting, and the figurines on the mantle have some definition in their shape. The subject is clearly sharper than any other element in the image. Had I been able to capture the angle, light and expression of the original shot with this lens, from this distance, I might have gotten a very sinister PR shot for this play based on Agatha Christie's Ten Little Indians.

A wider lens at the same aperture and lens-to-subject distance automatically produces greater depth of field. This was shot at 55mm and f/2.8, approximately 10 feet from the subject. As you can see, Frank, the wallpaper, the chair back, and the fireplace stones are relatively sharp, and the Indians are clearly recognizable as Indians. Unfortunately, it lacks the powerful expression and lighting of the first image, which were only enhanced by its shallow depth of field and telephoto lens compression.

Next week I’ll share more examples from this rehearsal to illustrate how too little, too much, or misplaced depth of field can dramatically alter our perception of an image. By the way, had I shot the first image at f/4 or f/5.6, I probably would have nailed it, except that it’s already at ISO6400, so I would have needed a slow shutter speed that would rob the image of sharpness through camera shake. I like the image very much, but it doesn’t suit the purpose of promoting the play.

Leave a comment

Filed under Camera Gear, Camera Settings, Dance and Theater

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s