Natural Art: The Photography of Brad Hill

 
Just How Much DoF??

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In the Field

Just How Much DoF? Findlay Creek, BC, Canada. March 12, 2011.

"Just" an image of a squirrel - shot shortly before photo tour and seminar season - and for a reason! Read on...

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. Use a larger aperture and your DoF (loosely defined as the area of sharp focus in front of and behind your focal point) decreases; use a smaller aperture and your DoF increases. Simply as pie, right? Sort of. 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?

Before I address these questions, I'm going to digress for a second. 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 with 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 those pesky questions! ;-)

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

If you're like about 1% of the photographers out there who has actually read their camera's manual (which includes me by the way), you'll think the answer to this question is dead-simple: Why - you dolt - you just push your "Depth of Field" preview button (of course)! Right. Ever try that while trying to focus on a swimming grizzly? Or even a fast moving squirrel? If you have, you'll probably agree that's a pretty useless button (which, hopefully, you can re-program to do something useful with!).

OK - how 'bout option 2 - using the DoF etchings on your lens's focusing scale on the barrel of your lens. Hmmm...this may be the only method WORSE than using the DoF preview button - I just checked my 200-400mm zoom - has no aperture values on it. My 400mm f2.8 VR is MUCH better...it has f22 (only) marked on it. That's real useful!

Hmmm...how 'bout option 3 - consulting depth of field tables? Well...that's a better option - I have "high-tech" DoF tables with me in the filed on both my iPhone and, when I bring it, on my iPad. But, even with these handy-dandy tools I find there are lots of times when, in the "heat of the action", it simply isn't convenient to consult them.

So what do I do? Something decidedly old-fashioned - I memorize the DoF values for some some specific distances and apertures for my key lenses. So...for instance...I know that when I'm photographing a bear at 20 meters with my D3s and 600mm f4 lens, I have about 10" of DoF at f4, 20" at f8, and 40" at f16. Add just a few more "data points" to your memory banks and you end up with a real good handle of your DoF when in the field. Takes a little work, but real handy in the field!

In the case of this squirrel, I was using a camera/lens combo that I don't use too often, so I ended up having to consult DoF tables on my iPhone. It told me that when using a 800mm lens on a DX Nikon camera and focused at a distance of about 30', I had about 3" of DoF at f16. I wanted both the facial region of the squirrel and the stump in focus, so I knew that I had to wait until the squirrel positioned itself in such a way that those two objects were within 3" of the same distance to my camera (i.e., they were close to being on the same vertical plane).

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

The first question was a technical issue - this one touches more on the aesthetics of an image and is much more subjective and thus 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. In this image I wanted the eye drawn to the eye and nose region of the squirrel, so I was more than willing to have the distal portions of the back slightly out-of-focus to add to this "effect". 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.

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.

PS: Many folks seem very interested in the "new" TC-20EIIII 2x teleconverter and are looking for sample images of it in action. For this reason here's some higher res images of this shot for your downloading pleasure! The BEST image to use to assess image sharpness is the full-res version of the shot (and view it at 100% on your monitor), but if you have a lower-speed internet connection grabbing the "half res" shot will give you a pretty good handle on the image sharpness.

• Very well-mannered Red Squirrel: Half res (2464x1632 pix; 1.2 MB) and Full res (4928x3264 pix; 4.9 MB)

NOTE: This image was captured with the 2x TC paired with a very fine "host" lens - Nikon's 400mm f2.8 VRII - don't assume results taken with other host lenses would produce similar quality.

Behind the Camera

Just How Much DoF? Findlay Creek, BC, Canada. March 12, 2011.

Digital Capture; RAW 14-bit format; ISO 180.

Nikon D7000 with Nikkor 400mm f2.8 VRII lens paired with TC-20EIII 2x teleconverter (total effective focal length of 1200mm). Supported on tripod with Wimberley head. VR on and in "Normal" mode.

1/160s @ f16; -0.67 stop compensation from matrix-metered exposure setting.

At the Computer

Just How Much DoF? Findlay Creek, BC, Canada. March 12, 2011.

RAW Conversion to 16-bit TIFF, including first-pass/capture sharpening using Phase One's Capture One Pro 6.

Further digital corrections on 16-bit TIFF file using Adobe's Photoshop CS5 and Light Craft's LightZone. Photoshop adjustments included selective exposure adjustment, and selective sharpening for web output. Final tonemapping and contrast/tone tweaking - especially to midtones - performed with LightZone using the tonemapper/re-light tool.

Conservation

Just How Much DoF? Findlay Creek, BC, Canada. March 12, 2011.

Ten percent of the revenue generated by this image will be donated to Wildsight.

Species Status in Canada*: This species is not designated as at risk.

The North American Red Squirrel (Tamiasciurus hudsonicus) is a small, rusty coloured squirrel distributed throughout most of Canada and in both the western mountains and Appalachian mountains of the United States. While the Red Squirrel is not considered under any threat as a species, some local populations are declining as the larger and more ecologically aggressive Grey Squirrel expands its range. In Calgary, Alberta, for example, the Grey Squirrel has replaced the Red Squirrel throughout most of the city over the past 30 years or so.

This Red Squirrel was photographed in the Columbia Valley of the East Kootenays. While this species is not currently not considered at risk in the Kootenays, it is vulnerable to habitat loss due to logging activities. Many ecosystems within the Columbia Valley face development pressure, including pressure from logging operations. Wildsight is an effective conservation organization that protects biodiversity and promotes sustainable communities in Canada's Columbia and Rocky Mountains. Support for Wildsight, through donation or becoming a member, will help ensure that they remain effective in their efforts to conserve threatened or endangered species and ecosystems.

*as determined by COSEWIC: The Committee on the Status of Endangered Wildlife in Canada.