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Ask a National Geographic Photographer

Mark Thiessen

Every month, National Geographic staff photographer Mark Thiessen answers your photography questions—and spills the secrets behind the shots.

Widely published in books and magazines, Thiessen has been on staff at National Geographic since 1997. He's covered subjects from the discovery of the U.S.S. Yorktown to the search for other Earths. He's also a certified wildland firefighter.


June 2008

Q: Is there a digital setting equivalent to exposing for the shadows and processing for the highlights? I'd like to get as broad a tonal range as I can with my digital camera.

A: In digital photography, if you expose for the shadows there is a good chance you will overexpose the highlights to an extent that they can't be brought back. However there are a couple of techniques you can use.

Using Aperture's Highlights and Shadows tool is the best way to optimize your image's exposure in the highlights, mid-tones, or shadows without compromising detail in the other areas of tonality. This is particularly useful when adjusting images of clouds or snow or images correctly exposed for the shadow areas.

Use the highlights parameter when you want to adjust the brightness values in the highlight areas of the image without affecting the mid-tones and shadows. Although the human eye is more sensitive to details in shadow areas than in highlight areas, such as snow, there is usually a fair amount of visual information that you can retrieve in the highlights.

Another technique for expanding the tonal range of your image is known as high dynamic range (HDR) photography. If you are in a contrasty situation, you take several exposures in order to capture information in both the brightest highlights and deepest shadows of the scene. Then you use special software such as HDRsofts's Photomatix to blend the different exposures into a less contrasty image.

For example, take three exposures of your scene at different exposures: -2 (two stops under), 0 (correct exposure), and +2 (two stops over). Photomatix would blend the highlights of the -2 exposure with the mid-tones of the 0 exposure and the shadows of the +2 exposure. The result is a full-tone image with good detail in the highlights and shadows.

Q: How do you steady your hand to prevent camera shake if not using a tripod or monopod?

A: There are several techniques for preventing camera shake when shooting at slower shutter speeds.

First I'll point my left shoulder at the subject. Next I'll brace the left corner of the camera on my left shoulder so I'm shooting along my body. Finally, I'll hold my breath while I press the shutter release. Some photographers carry a small beanbag or steady their camera on their camera bag.

If you need to make long time exposures, use the self-timer to trip the camera so you don't shake the camera while pressing the shutter release. If you are outside, try bracing yourself against a tree or the side of a building. When inside use a doorway or a chair as a tripod.

Q: What kind of optical filters, if any, would you use while photographing animals, landscapes, people, and night scenes?

A: There are a ton of photography filters on the market that range from slight color correction to crazy special effects. Personally, I only use a polarizer or neutral density filters. I feel the rest are gimicky and give your images a fake look.

A polarizing filter is handy because it can reduce reflections and glare while deepening the blue sky. It has a moveable outer ring that you twist to find the maximum point of polarization. Some autofocus mechanisms are thown off by polarizing filters. Make sure you use a circular polarizer to avoid these problems.

A neutral density filter, as the name implies, is neutral because it has no color. It also reduces the amount of light that enters the camera lens, enabling the photographer to use a slower shutter speed or larger aperture in bright light. Think of it as sunglasses for your camera. They are available in various densities.

Q: Which lens should I use for macrophotography?

A: There are several lens options for doing macrophotography.

Extensions tubes are essentially hollow tubes that connect between your camera body and lens. They allow your lens to focus closer but also cut down on the light reaching your sensor.

Reversing rings let you mount your camera's lens backwards so the front of the lens is facing the sensor. With removable lenses that weren't designed for macrophotography, reversing the lens can produce sharper results and increase the magnification.

Close-up filters screw on the front of your lens and come in varying degrees of magnification: +1, +2, +3, etc. You can use just one or several in combination to get very close.

Macro lenses are the most expensive option. They are special lenses that are designed to focus very close. They come in roughly 50mm and 100mm sizes. The 100mm lets you shoot close-ups while being a little farther away.

Q: Do you recommend using a lens hood? If so, what are the benefits?

A: Bright light sources within or just outside the field of view cause lens flare. It is an effect produced by the reflection of light internally among elements of an optical lens. A lens hood shades the lens, protecting it from light coming from outside the picture area, which can reduce contrast. I frequently use a lens hood to cut down on lens flare and to protect the lens from raindrops.

Q: What's the best way to take pictures of subjects that don't have good contrast between it and the background? For instance, a bird sitting on a branch of a tree with a lot of foliage.

A: The best way to separate your subject from a similarly toned background is to shoot it during a time of day when the light strikes your subject but not the background. This could mean waiting until the bird is in the right position on the branch or until the sun is shining at a low angle. You can also use the widest aperture (lowest f-stop number) you have. This will put the background out of focus and help separate your sharp bird from the blurry background.

Q: Do you use medium-format digital cameras?

A: I use medium-format digital cameras in the studio at National Geographic. They range in resolution from 22 to 36 megapixels and are very expensive but give unsurpassed resolution for better detail. The raw files convert to 100 MB for each picture, so lots of storage is required.

Q: How can I take good night shots, such as of the northern lights, with my digital camera?

A: First you will need a tripod to steady your camera during the long time exposures. Some point-and-shoot digital cameras have a night shot setting (look for the moon-and-stars icon). This allows you to take long time exposures. Some cameras have a bulb (B) setting that opens the shutter as long as you have the shutter release pressed. You will also need an electronic cable release to trip your camera without touching it.

Another method is to set the self-timer for a few seconds and press the shutter release. This will give the camera shake time to settle down by the time the shutter opens.

To get the best night shots, use a tripod and set your camera on manual exposure mode. If you use the other automatic exposure modes, your camera will be fooled by the night scene and try to make it daylight, resulting in overexposed night shots. Set your f-stop around 5.6, and then try different lengths of shutter speeds until you get something you like.

Be careful of judging the exposure of your image in your camera's LCD monitor at night. The monitor will be very bright when viewed at night and can trick you into thinking your properly exposed pictures are overexposed. Until you get a feel for it, shoot lots of different exposures that you can view in the standard viewing environment of your computer monitor.

Q: Have you ever shot with infrared film? If so, do you have any tips, warnings, or lessons learned to share?

A: I have only shot with color infrared film. It's very tricky. I recommend you use a deep yellow filter on your lens and set your camera at 100 ISO if using Kodak's Ektachrome Professional Infrared film (EIR). Be sure to bracket your exposures (shoot some lighter and some darker) as the exposure latitude is very narrow.

The film can be tricky to handle as well. It needs to be frozen until you are ready to use it, then warmed up to room temperature before you use it. About two hours will do it. It has to be removed from the film can and loaded into the camera in total darkness. You can use a film-loading bag to do this in the field. After the film is exposed, you have roughly 24 hours to have the film processed, because the emulsion will deteriorate.

Images produced with color infrared film have a unique look. Once you understand how the film interprets colors and how you can control it with color filters, you can make it work for you creatively. It's not likely you'll use this film all the time, but it could become one you come back to when you're looking for something a little different.

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