[ 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.
Because so much of the scene is captured by such lenses, it's easy to include too much in the photograph. With this all-encompassing range, an image can have so many details that the viewer is unable to focus on any central point.
Rather than simply getting in as much as you can within the frame, consider traditional compositional elements, such as leading lines, contrasting textures, highlights and shadows, to draw attention to the most important parts of your scene. Although this is applicable to any focal length, it can be particularly important when using extreme wide-angle lenses.
[ Telephotos ] Telephoto lenses bring distant objects closer. Moderate telephotos, ranging from 85mm to 200mm, and super-telephotos of 300mm and longer, have a narrow field of view that creates an emphasis on individual details that otherwise might be lost with a wider focal length.
Another inherent quality of the telephoto lens is an optical effect called compression. Compression gives the impression that objects appear closer to each other than they actually are. This effect creates a sense of proximity between distant objects that can serve as a means of contrasting elements in a scene. You could isolate a stand of trees against a distant mountain range and create a sense of scale, for example.
Compression can be useful for capturing a variety of textures or patterns that exist in a scene. In a photograph taken in the desert, for example, the frame can consist of a pristine foreground of sand, the undulating rise and fall of the dunes and the rising mountain ranges in the background. These elements are compressed and isolated by the telephoto lens, resulting in an image where the different textures and shapes serve as contrasting elements in the final photograph.
Compression also can be used effectively with contrasting tones in an image. If a scene includes a group of white aspens in front of a darker stand of trees, the proximity created by the telephoto lens boosts the difference in color and tone, producing a shot with significantly more impact than might be achieved with a wider focal length in the same camera position.
By knowing your lenses when composing landscape images, you'll have what you need to create a piece of art rather than a snapshot.
[ Zoom Vs. Fixed Lenses ] It used to be that fixed focal-length or prime lenses were considered far superior to zooms. That's no longer the case. Many zoom lenses offer optical quality comparable, if not superior in some cases, to their prime siblings. So why choose a fixed focal length over a zoom? There are several reasons.
The first one is speed—not how fast the lens can focus, but rather the lens' maximum aperture. Many fixed focal-length lenses offer a maximum aperture of ƒ/2.8 or ƒ/4. For example, a fixed 300mm ƒ/4 lens will provide a full stop of light more than a 100-300mm ƒ/3.5-5.6, which has an effective aperture of ƒ/5.6 at its 300mm setting.
Hence, the lens gathers more light for a brighter image in the viewfinder and maintains an exposure with a higher shutter speed under low light conditions. In addition, because more light is coming through the lens and reaching the AF sensor, the camera has a better chance of quickly achieving autofocus.
Variable-aperture zoom lenses transmit less light whenever you create its telephoto range. For example, a 24-120mm ƒ/3.5-4.5 lens starts off with a relatively wide aperture, but by the time it reaches its 120mm focal length, you've lost almost a full stop of light. This means that if you were shooting at a shutter speed of 1/30 sec., you'd have to decrease the shutter speed to 1/15 sec. to maintain the same exposure. You'd likely end up with a soft image because of camera motion or even shutter vibration.
There are zoom lenses with a constant aperture, but generally they're considerably more expensive than their variable-aperture versions. If you can afford them, they're a worthwhile investment, especially since you're shooting
Fixed focal-length lenses also are subject to less spherical aberration, such as pincushioning and barrel distortion. Appearing as bowing toward the edges of the frame, these distortions usually are evident with wide-angle zoom focal lengths, where straight lines are slightly curved inward (pincushion) or outward (barrel). Although highly corrected, some zooms do better than others in this respect.