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Sunday, August 1, 2004

Lenses [And The Landscape]

Film Vs. Digital | Zooms | Wide-Angles | Telephotos | Zooms Vs. Fixed

It's easy to just pick the widest lens in our bag and shoot landscapes, but that won't guarantee a successful shot. Instead, it's important to consider the strengths and weaknesses of a variety of focal lengths before committing. Even if you're using a zoom lens, you should carefully consider what focal length will best capture those telling elements of a scene.

Lenses and the landscape[ Film Vs. Digital ] Although the information in this article is applicable to both digital and film cameras, focal lengths will be related to the 35mm format. Because most image sensors are smaller than 35mm, the actual focal length may have little relation to what you expect based on 35mm. The way a lens/sensor combination responds to a scene is totally dependent on the size of the sensor. The result usually is subject to magnification within the image frame. For example, a 100mm lens attached to a digital SLR with a 1.5x magnification factor performs as a 150mm lens would on 35mm. We'll use the convention of 35mm focal lengths for reference here, so compare lenses with your camera by using 35mm equivalents.

[ Zoom Lenses ] Zoom lenses have usurped fixed focal lengths as the lens of choice for all aspects of photography, including landscape. Their optical quality often rivals those of prime lenses with the added convenience of multiple focal lengths within a single lens. What makes these lenses so much better than they were 20 or more years ago? Well, computer-aided design and the use of aspherical and low-dispersion elements have gone a long way to producing high-quality optics.

Aspherical lenses are specially shaped elements that correct for a variety of optical and color aberrations that occur within an optical design. To create consistent optical quality throughout a zoom range, lenses use one or more aspherical elements to correct spherical aberrations (pincushioning and barrel distortion) as well as improve contrast and sharpness. Aspherical elements reduce the need for multiple glass elements, thereby creating a smaller and more compact lens.

An increasing number of lenses—fast-aperture, telephotos and ultra-wides—also are incorporating low-dispersion elements in their design. These elements correct for chromatic aberrations, which can lead to decreased color accuracy, particularly toward the edge of the frame. You've seen dispersion when viewing light through a prism, which is dispersed into its component light waves, creating a fan or spectrum of color. Although pretty to look it, it's bad news when you're trying to photograph a scene. The use of low-dispersion elements ensures that the path the light travels through the lens remains concentrated and stable, guaranteeing color accuracy and image brilliance.

[ Wide-Angles ] Wide-angle lenses always have played a big role in landscape photography. Lenses like the 24mm and 28mm have been a staple for a long time. Although wider lenses were used, they often were prohibitively expensive for anyone other than the professional photographer. Now, lenses as wide as 14mm or more are available at a more accessible price point. These lenses not only provide a wider angle of view, but are a dynamic, creative option.

The wider the focal length, the greater the field of view. For example, a 28mm lens gives you an angle of view of 74 degrees. Attach an 18mm lens to your camera and the field of view increases to 100 degrees. If you're unable to move farther back to capture more of the scene, a wider lens can deliver the increased angle of view you need.

Some prime wide-angle lenses are designed to be rectilinear, which means that straight lines remain straight when shot with such a lens. Extreme wide-angle lenses, even as wide as 14mm, can afford an ample field of view with rectilinear performance.

Specialty lenses also are available as prime lenses. With a field of view of 180 degrees or more, fish-eye optics offer an unusual way of looking at the world. Traditional fish-eye lenses created a circular image within the rectangular frame. Now there are full-frame fish-eyes that provide the same angle of coverage, but utilize the full rectangular frame. Unlike rectilinear lenses, curvature will be evident toward the edge of the frame, though you'll have a much greater angle of view.

As well as allowing increased coverage, wide focal lengths offer greater depth of field, which results in objects in an image appearing sharp despite being far apart. You can compose a distant mountain range with a strong foreground object and keep both in focus, for instance. Such a composition creates a dynamic counterpoint to the background and results in a greater sense of depth and perspective.

Perspective can change dramatically with wide-angle lenses by simply changing where you position the camera. Imagine you have large rocks in the foreground of a landscape. By switching to a wider lens and remaining in the same position, the rocks become less prominent objects in the photograph. If you want to emphasize them for the sake of composition, lower the camera and move closer to the formation, thereby increasing the apparent size of the rocks in relation to their surroundings. This change in perspective can produce a much more successful image.


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