Just How Much DOF?

Spring is hitting my home range right now, an I'll be spending more time in the field and leading a lot of photo tours and workshops in the next while. So...over this past weekend I decided to test some new gear and capture some teaching images. So I plunked myself down along one of the local "squirrel highways" and nabbed some shots...

One of the very first thing novices learn when they acquire their first SLR is that the "depth of field" (or DOF) of an image varies with the aperture used to capture that image. Yet, on the instructional photo tours I lead I get two questions very, very frequently - and often from highly experienced photographers. The questions?

1. How DO you determine DOF when capturing wildlife images in a field setting?

2. Even if I know HOW to control my DOF in the field, what is the "right" amount of DOF for a given situation?

It's impractical to deal with both of these questions here, so I'll just ramble on a bit about question 2 here - the aesthetic aspects of DOF. But first, a tiny bit of context...

Unlike studio photographers, nature photographers - and particularly wildlife shooters - have very little control over the conditions under which they capture their images. The vast majority of the time we can't (and don't want to!) control what our subject is doing or control other critical variables, like lighting. BUT, one thing we have some control over during image capture is the aperture we choose and, consequently, our DOF. Of course, available light and exposure issues limit our control, but thanks to the new generation of DSLR's that perform so well at moderate to high ISO's, we now have more control over our aperture and DOF than ever before. Ensuring you know how to "harness" that DOF is absolutely critical to capturing visually interesting images...

Now back to that pesky question #2...

The question of "what is the right amount of DOF" touches on the aesthetics of an image and is much more subjective and thus totally open to debate. But here's my take on the creative aspects of using DOF effectively. I'm a huge believer that the philosophy of "simplify and isolate" (simplify your composition, isolate your subject) is a great "mindset" for a wildlife photographer to take into the field. One way of "simplifying and isolating" is to use a narrow DOF to remove distractions from the background of an image.

I'm also a real believer in the concept of "visual contrast", i.e., that the eye is drawn by contrast in any of a number of visual differences in a scene - differences in light (traditional contrast), differences in colour, differences in apparent motion (think "panning" with a sharp subject with blurred background), and differences in image sharpness. When you apply this "visual contrast" model to DOF, it basically says the eye will be drawn more to sharp regions in an image if there is a sharpness differential in a scene, i.e., that parts of the image are out-of-focus. And, by the way, I also believe that having distinct soft out-of-focus zones in an image can contribute to the apparent sharpness of the portions of the image that ARE in focus.

In the case of this image I wanted the eye drawn to the eye and nose region of the squirrel, so I was more than willing (and even happy) to have the distal portions of the back slightly out-of-focus to add to this "effect" (of drawing the eye). And, of course, I wanted the background totally soft and distraction free...

The moral of the story? Simply this: knowing how to control and effectively use your DOF in a field setting is a huge asset for a wildlife photographer to have. Knowing (and judging) your DOF is a technical task, but choosing the one that will best help you to achieve your aesthetic goal is a creative endeavor. Just another instance of the right-brain, left-brain "cooperation" that's needed in wildlife photography.

Subject: Red Squirrel (Tamiasciurus hudsonicus) mugging for the camera
Location:Findlay Creek, BC, Canada
Camera: Nikon D7000
Lens: Nikkor 400 mm f/2.8 VRII lens paired with TC-20EIII 2x teleconverter (effective focal length of 1200mm).
Exposure: 1/160s at f16. ISO 180. -0.67 stop compensation from matrix metered exposure.
Crop: None - this is full frame.

If you're interested in my thoughts on question #1 above, I have an even longer () discussion about this topic on my website where I address some ways to assess your DOF in the field. Just click on the "In the Field" tab for the discussion...

http://www.naturalart.ca/galleries/latest/.

If there are any Nikon users who are curious about that 2x TC - there's links to 100% res images on my website (just use that same link above)

Comments and feedback greatly appreciated...probably better to view larger version prior to doing so...

Cheers...

Brad