Enigmatic Autofocus

Focusing Is For The Birds • The Dark Side Of Long Exposures • Big Images From Small Files • To Tilt Or Not To Tilt

This flock of shoveler ducks was taken with a Canon EOS 7D set to ISO 400 and an EF 500mm lens with a 1.4x tele-extender (700mm + 1.6x). The exposure was 1/1000 sec. at ƒ/11. I had preset my focus by setting it on a stationary subject at the distance I expected the birds.

Focusing Is For The Birds
Q When photographing birds with long telephoto lenses set to autofocus, I’m having problems with the lens searching first to the closest point of focus, then out to infinity, before locking onto the subject. Since the birds are usually far away, I want the lens to focus to infinity first. Waiting for the lens to go through most of its focus range while the bird flies away is frustrating! Is this a lens or a camera problem? Can the camera firmware be changed to focus first at infinity?
R. Rockwood
Portland, Oregon

A Autofocus is a cooperative function of the camera and the lens. Even if you could, you wouldn’t want to change your camera’s firmware to always seek focus at infinity first because infinity with long lenses is a long, long way away. You would compromise your autofocus capability for the majority of subjects. There’s a better solution.

Most long telephoto lenses have a limiting switch that gives the choice of enabling either the full range of focus or only a distant range of focus. I hope your lenses have this capability; if not, you might want to consider a new purchase. Anytime I’m photographing birds in flight (or any subject moving quickly at a distance, such as runners, race cars or aircraft), I set the lens to the longer range to prevent exactly the problem you describe. It significantly speeds the lens’ ability to attain the subject quickly because if the lens is focusing first at its closest point, the subject in the distance is so far out of focus as to be undistinguishable to both the photographer and the lens/camera.

A technique I use to narrow the range even further when photographing birds in flight is to find a stationary object at the approximate distance at which I anticipate photographing the birds. I preset the focus on that subject, and then when I activate the autofocus on the birds themselves, the adjustment is small enough from the outset to enable a fast lock.

The Dark Side Of Long Exposures

Q I’ve seen images where water or surf appears very milky and smooth, sometimes even cloudlike. I’ve read that a neutral-density filter makes it possible to get such an effect. However, when I go beyond three stops using a Vari-ND filter, the image appears very dark in the viewfinder of my Canon EOS 7D. How does one use the Vari-ND filter, or any other filter, to achieve that dreamy look with water?
S. Kekre
Marietta, Georgia

A Neutral density (ND) filters limit the amount of light entering the lens, allowing a long exposure even in bright conditions. There are a number of single-density ND filters you can use to achieve the effect you want; they’re generally offered in two-, three- or four-stop increments, meaning that the filter cuts the light by the equivalent of a two-, three- or four-stop reduction in the lens aperture. The Singh-Ray Vari-ND offers a range of two to eight ƒ-stops of neutral density.

Here’s the process. First, set your composition and focus without using any filtration; if using a single ND filter, remove it. If using the Vari-ND, set it to its lightest setting (two stops).

Next, determine the shutter speed you need to render the water movement. With an ocean scene such as you describe, I might choose a several-second-long exposure to cover several wave patterns. With a waterfall, I might set the exposure in the area of 1/8 to 1/4 sec. Choose the rest of your camera settings (ƒ-stop and ISO) to support the shutter speed you want. If you’re using a single ND filter, you won’t have a lot of range to work with; only one ƒ-stop and ISO setting will probably support your shutter speed. The advantage of the Vari-ND is significant. With that filter on my lens, I can first set the exposure and shutter speed I want, then dial the filter to the setting that works with my combination.

To check and fine-tune the exposure, take a picture; look at the resulting image on the LCD screen. Then check the histogram to confirm you’ve achieved the correct exposure. Pay particular attention to the white end of the histogram to be sure that the milky water, usually the brightest part of the scene, isn’t blown out. If you have pixels up against that right wall, you’re overexposed.

Big Images From Small Files
Q I came across your note in a previous column (Jan./Feb. 2010) about making large (40x40) prints of images captured with small cameras, such as an iPhone. How can you do that without losing much of the image clarity?
S. Zaiontz
Via the Internet

A Well, it’s not about clarity. It’s about creativity. You can’t maintain the detailed information in a small iPhone capture if you enlarge it very much at all. If you do, the pixels themselves become a prominent part of the final image. The iPhone used for Dewitt Jones’ great images (referred to in the earlier column) has only 2 megapixels, enough for use on the phone’s small screen and to view in small sizes on a computer monitor. (Even if Dewitt has upgraded to the new iPhone, he still has only 5 megapixels.) To create a large-format print from an iPhone file, you need to move far from your original capture by processing and “tweaking” it a number of times. First, add special effects using apps in the iPhone (such as Photogene, Photo fx or CameraBag, to name a few), then interpolate the image to new dimensions and add even more layers of creative manipulation and give a painterly look with software such as the Topaz Clean and Simplify plug-ins for Photoshop. The file becomes a new photograph loosely based upon the basic forms and colors of the original.

Why would you do this? Because you can! No, that’s not the only reason. You probably take your iPhone everywhere you go, and even if you don’t have cell service, you still can use it to take advantage of an unexpected photo opportunity. If you have colors and shapes, you have your starting point. But if you want true, absolute, tack-sharp, high-resolution detail in a big print, you still have to capture it with a professional-level DSLR and high-quality lens, using all the techniques and equipment required to eliminate blur and gather as much detail as possible.

To Tilt Or Not To Tilt
Q I stumbled upon an article on Ansel Adams on the OP website (see “Shoot Like Ansel Adams With 35mm DSLRs,” 6/1/2008). A few of your photos were used as examples, using a tilt/shift lens for landscapes. What’s the advantage of a tilt/shift over shooting at a smaller aperture? Would it be worth investing in a tilt/shift for landscape photography?
N. Reed
Via the Internet

A A tilt/shift lens has front elements that can be tilted, which changes the plane of focus to more efficiently apply depth of field (the range of sharp focus) across a landscape. (If you want to know more about how and why this works, research the Scheimpflug Principle.) Used to maximum advantage, a tilt/shift lens can render a scene sharp from close foreground to distant background, as when photographing a field of flowers in an alpine meadow ringed by high mountain peaks. This apparent increase in depth of field can be achieved even with larger apertures, allowing shutter speeds fast enough to stop the movement of vegetation in a landscape. The use of very small apertures to achieve the same depth of field may compromise sharpness due to diffraction and/or movement of the subject or camera being emphasized by slow shutter speeds.

Tilt/shift lenses from Nikon and Canon come in a wide range of focal lengths, from 135mm to an ultra-wide 17mm. They’re expensive, but very useful for landscape photographers. I carry at least two tilt/shift lenses, the 90mm and 24mm Canons, when concentrating on scenic images.

The tilt/shift lens is useful in other ways, too. The shift aspect of the tilt/shift lens works to overcome vertical distortion (often a problem in architectural photography) and to capture three-image panoramas across the image plane.

Should you buy one? It depends on how serious you are about your landscape photography. There are other ways of increasing depth of field with any of your lenses (if there’s no movement occurring within the scene). You can take multiple images with different focus planes by moving through the subject from near to far and capturing slices of overlapping areas of focus. These multiple images can be assembled in either Photoshop CS5 or the stand-alone program Helicon Focus. The multiple-image composite technique enables virtually unlimited sharpness under ideal conditions, whereas the tilt/shift lens may solve depth-of-field problems in windy conditions as well. [Editor’s Note: An article by Willard Clay in this issue of OP describes several techniques for shooting and combining multiple images to achieve deep focus.]

For information about upcoming seminars and digital-imaging workshops, visit www.georgelepp.com. If you have any tips or questions, address them to: OUTDOOR PHOTOGRAPHER, Dept. TT, George Lepp, 12121 Wilshire Blvd., Suite 1200, Los Angeles, CA 90025-1176 or online at www.georgelepp.com.

One of North America’s best-known contemporary outdoor and nature photographers and a leader in the field of digital imaging and photographic education, Lepp is the author of many books and the field editor of Outdoor Photographer magazine. One of Canon’s original Explorers of Light, Lepp finds inspiration in advancing technology that fuels creative innovation and expression of his life-long fascination with the natural world.

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