by Gerald Boerner
Camera lenses for Single-Lens Reflex (SLR) cameras create a greater selection challenge than that encountered when purchasing a compact (digital) camera. In the latter case, we select a camera where the lens meets our requirements while in the former case the camera body often is purchased without a lens at all. A wide variety of lenses are generally available for any particular camera body we purchase.
The interchangeable lenses available for any particular camera are limited only by the cost of the lens and the type of lens required for our particular photographic project. A major limitation does exist: a lens for one brand of camera, e.g., Canon, will NOT work on a different brand, e.g., Nikon. But within a camera manufacturer a wide range of lenses are generally available from both the camera’s manufacturer and other third party suppliers.
Today we will examine the different types of lenses that are available and what features they provide. We also provide you with some important dimensions that you will want to consider in selecting a lens or lenses for your SLR. GLB
“The photographic image… is a message without a code.”
— Roland Barthes
“The series of photographic operations, developing, washing, final drying, takes about quarter of an hour.”
— Gabriel Lippmann
“When you start out, you’re not really aware. I didn’t have a sense of photographic history.”
— Herb Ritts
“Photographers deal in things which are continually vanishing and when they have vanished there is no contrivance on earth which can make them come back again.”
— Henri Cartier-Bresson
“When the object that is produced, the photographic image has the ability to make tears come to your eyes; to inspire you to the point where you have to catch your breath, then nothing else matters.”
— John Sexton
“The creative act lasts but a brief moment, a lightning instant of give-and-take, just long enough for you to level the camera and to trap the fleeting prey in your little box.”
— Henri Cartier-Bresson
“What I’m exploring right now is the subject of my own mortality. It’s an area that I’m curious about, and I’m researching it to see if there’s a photographic essay in it for me. If images don’t start to come, I’ll go to something else.”
— Leonard Nimoy
“Memory is very important, the memory of each photo taken, flowing at the same speed as the event. During the work, you have to be sure that you haven’t left any holes, that you’ve captured everything, because afterwards it will be too late.”
— Henri Cartier-Bresson
Focal Concept/Technology: SLR Lenses Explained
An SLR camera stands for single lens reflex camera. One of the unique factors about this type of camera is interchangeable lenses. Depending on how the camera will be used, different lenses can be attached to maximize the camera’s effectiveness. Different lens qualities include prime or zoom, focal length, aperture, focus type and lens quality
Interchangeable Lenses
The major advantage of SLR and DSLR cameras is the possibility of changing lenses, to select the best lens for the current photographic need, and to allow the attachment of specialized lenses. Film SLR cameras have existed since the late 1950s, and over the years a very large number of different lenses have been produced, both by camera manufacturers (who typically only make lenses intended for their own camera bodies) and by third-party optics companies who may make lenses for several different camera lines.
DSLRs became available around the mid-1990s, and have become extremely popular in recent years. Some manufacturers, for example Minolta, Canon and Nikon, chose to make their DSLRs 100% compatible with their existing SLR lenses in the beginning, allowing owners of new DSLR’s to continue to use their existing lenses and get a longer lifespan from their investment. Others, for example Olympus, chose to create a completely new lens mount and series of lenses for their DSLRs.
As implied by the above, lenses are only interchangeable within the "mount system" for which they are built. It is not possible (at least not without an adapter) to mount, for example, a Pentax lens on a Sony camera body.
Focal length and angle of view
The focal length of a lens, together with the size of the image sensor in the camera (or size of the 35 mm film), determines the angle of view. A lens is considered to be a "normal lens", in terms of its angle of view on a camera, when its focal length is approximately equal to the diagonal dimension of the film format or image sensor format. The resulting diagonal angle of view of about 53 degrees is often said to approximate the angle of human vision; since the angle of view of a human eye is at least 140 degrees, more careful authors will qualify that, for example as "similar to the angle of crisp human vision.” A wide-angle lens has a shorter focal length, and includes more of the viewed scene than a normal lens; a telephoto lens has a longer focal length, and images a small portion of the scene, making it seem closer.
Lenses are not labeled or sold according to their angle of view, but rather by their focal length, usually expressed in millimeters. But this specification is insufficient to compare lenses for different cameras because field of view also depends on the sensor size. For example, a 50 mm lens mounted on a Nikon D3 (a full-frame camera) provides approximately the same field of view as a 32 mm lens mounted on a Sony α 100 (an APS-C camera). Conversely, the same lens can produce different fields of view when mounted on different cameras. For example, a 35 mm lens mounted on a Canon EOS 5D (full-frame) provides a slightly wide-angle view, while the same lens mounted on a Canon EOS 400D (APS-C) provides a "normal" or slightly telephoto view.
In order to make it easier to compare lens–camera pairs, it is common to talk about their 35 mm equivalent focal length. For example, when talking about a 14 mm lens for a Four Thirds System camera, one would not only indicate that it had a focal length of 14 mm, but also that its "35 mm equivalent focal length" is 28 mm. This way of talking about lenses is not just limited to SLR and DSLR lenses; it is very common to see this focal length equivalency in the specification of the lens on a digicam.
Types of lenses
Standard
This will typically cover an 18-55mm
focal length range (around 27-90mm
equivalent), offering both a modest
wideangle setting and a mild
telephoto effect.
A normal lens is a lens that reproduces perspective that generally looks "natural" to a human observer under normal viewing conditions, as compared with lenses with longer or shorter focal lengths which produce an expanded or contracted field-of-view. Lenses of shorter focal length are called wide-angle lenses, while longer focal length lenses are often referred to as telephoto lenses.
In 35 mm photography, a "normal" prime commonly refers to a prime lens with 50 mm focal length, though that is somewhat longer than the film format diagonal of 43.3 mm, which is typically taken to define a normal focal length. Small sensor digital cameras will require shorter focal lengths (in the ratio of their crop factor) to have the same angle of view.
Prime lenses
Standard non-zoom lenses are called prime lenses or simply "primes". Their advantage, in addition to typically giving a slightly better image quality, is that they are smaller, lighter and cheaper than a zoom lens of the same quality. A prime lens may also be "faster", i.e., have a larger maximum aperture (smaller f-number), so it can be used with less light (with the same shutter speed), and can provide less depth of field in situations where this is desirable.
Compact 85mm Canon
prime lens with a maximum
aperture of f/1.8
The term prime has come to be used as the opposite of zoom; that is, a prime lens is a fixed-focal-length lens, while a zoom lens has a variable focal length. A prime lens of a given focal length is less versatile than a zoom whose range includes that focal length, but is often of superior optical quality, lighter weight, smaller bulk and lower cost. In comparison with a zoom lens, a prime lens has fewer moving parts and optimization for one particular focal length. With a less complicated lens formula they suffer from fewer problems related to chromatic aberration.
Prime lenses usually have a larger maximum aperture (smaller f-number) than zoom lenses. This allows photography in lower light and a shallower depth of field.
Wide-Angle Lenses
From a design perspective, a wide angle lens is one that projects a substantially larger image circle than would be typical for a standard design lens of the same focal length; this enables either large tilt & shift movements with a view camera, or lenses with wide fields of view.
One of Canon’s most
popular wide-angle lenses —
17-40 mm f/4 L retrofocus
zoom lens.
More informally, in photography and cinematography, a wide-angle lens refers to a lens whose focal length is substantially shorter than the focal length of a normal lens for the image size produced by the camera, whether this is dictated by the dimensions of the image frame at the film plane for film cameras (film format) or dimensions of the photosensor for digital cameras.
By convention, in still photography, the normal lens for a particular format has a focal length approximately equal to the length of the diagonal of the image frame or digital photosensor. In cinematography, a somewhat longer lens is considered "normal".
There is an easy formula for calculating the angle of view for any lens that produces a rectilinear image. In addition to giving a wider angle of view, the image produced by a wide-angle lens is more susceptible to perspective distortion than that produced by a normal lens, because they tend to be used much closer to the subject.
Zoom Lenses
A zoom lens is a mechanical assembly of lens elements with the ability to vary its focal length (and thus angle of view), as opposed to a fixed focal length (FFL) lens (see prime lens). They are commonly used with still, video, motion picture cameras, projectors, some binoculars, microscopes, telescopes, telescopic sights, and other optical instruments.
Nikkor 28-200 mm zoom lens,
extended to 200 mm at left and
collapsed to 28 mm focal length
at right
The focal length of a zoom lens is not fixed; instead it can be varied between a specified minimum and maximum value. Modern lens technology is such that the loss of image quality in zoom lenses (relative to non-zoom lenses) is minimal, and zoom lenses have become the standard lenses for SLRs and DSLRs. This is different from only 20 years ago when, due to image quality concerns, most professional photographers still relied primarily on standard non-zoom lenses.
Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or "4×" zoom. Typical zoom lenses cover a 3.5× range, for example from 24 – 90 mm (standard zoom) or 60 – 200 mm (telephoto zoom). "Super-zoom" lenses with a range of 10× or even 14× are becoming more common, although the image quality does typically suffer a bit compared with the more traditional zooms.
The maximum aperture for a zoom lens may be same for all focal lengths, but it is more common that the maximum aperture is greater at the wide-angle end than at the telephoto end of the zoom range. For example, a 100 mm to 400 mm lens may have a maximum aperture of 4.0 at the 100 mm end but only 5.6 at the 400 mm end of the zoom range.
Superzoom
The ‘superzoom’ is targeted at photographers looking for one lens that covers almost every shooting situation. Typically a superzoom will cover an 18-200mm or 18-250mm focal length range with just one lens.
However, while a superzoom gives you a focal length for every occasion, certain design compromises have to be made to cover the expansive zoom range. These compromises often translate into a reduction in image quality.
While superzoom lenses have improved greatly in recent years, they still have a number of drawbacks in comparison with shorter-range zooms and prime lenses. Most notable is the much increased likelihood of significant distortions of the image at both extreme ends of the range. Other potential problems include smaller maximum aperture and poorer autofocus performance.
Macro lenses
Macro lenses are designed for extreme close-up work. Such lenses are popular for nature shooting such as small flowers, as well as for many technical applications. As most of these lenses can also focus to infinity and tend to be quite sharp, many are used as general-purpose optics.
The classical definition is that the image projected on the "film plane" (i.e., film or a digital sensor) is close to the same size as the subject. On 35 mm film (for example), the lens is typically optimized to focus sharply on a small area approaching the size of the film frame. Most 35mm format macro lenses achieve at least 1:2, that is to say, the image on the film is 1/2 the size of the object being photographed. Many 35mm macro lenses are 1:1, meaning the image on the film is the same size as the object being photographed. Another important distinction is that lenses designed for macro are usually at their sharpest at macro focus distances and are not quite as sharp at other focus distances.
Special purpose lenses
Most users of SLR and DSLR cameras stick to using zoom lenses, while a few of the more adventurous amateurs and many professional photographers also invest in a few prime lenses. Special purpose lenses are, as the designation implies, for special purposes, and are not so common.
Special-purpose tilt-shift
lens for special effect
photographs
There are many different kinds of special purpose lenses, the most popular being fisheye lenses, which are extreme wide-angle lenses with an angle of view of up to 180 degrees or more, with very noticeable (and intended) distortion.
Some other kinds of special purpose lenses, such as perspective control lenses and soft-focus lenses, were more popular with film SLRs but are less popular for DSLRs because the same or similar results can be obtained with post-processing software.
For a more complete discussion of special purpose lenses see Special-purpose photographic lenses.
Key Considerations in Selecting a Lens
Mark Kennan, in his eHow article (see below for the reference), identifies the following characteristics of a lens that go into the determination of the best lens for a particular photography goal. They include:
Different lens qualities include prime or zoom, focal length, aperture, focus type and lens quality.
- Prime or Zoom:
Lenses can either be prime lenses or zoom lenses. Prime lenses are set at one focal length and cannot be adjusted, while zoom lenses offer the ability to change the focal length, or zoom in and out.
Focal length is how close or far the camera is able to zoom in and out. For taking pictures of objects that are close, use a wide-angle lens with a focal length of less than 35mm to be able to fit more in the picture. For taking pictures of far away objects, use a lens of 100mm or more.
Aperture represents the maximum amount of light the camera is able to let in. The larger the number, the less light the camera can let in. The smaller the number, the more light. Wide apertures, those of 2.8 or less, are considered "fast" lenses and are used to take pictures of sporting events and other fast moving objects.
Lenses can have manual focus, automatic focus or full-time manual focus. Manual focus allows the photographer to set the focus. When set to automatic, the camera does it automatically. Those lenses with full-time manual focus allow the user to adjust the focus that the camera has automatically set without having to switch the lens to manual.- Lens Quality:
Like most products, there are different levels of quality in lenses, with better-built lenses costing more. The better-built lenses produce higher quality images. For example, Canon designates its best lenses as "L" lenses.
References:
Barbara London, Jim Stone, & John Upton. (2008) Photography. Pearson, Prentice-Hall
Background and biographical information is from Wikipedia articles on:
Wikipedia: The Camera…
http://en.wikipedia.org/wiki/Camera
Wikipedia: Photographic Lens…
http://en.wikipedia.org/wiki/Photographic_lens
Web Sites and Blogs:
BrainyQuote: Photographic Quotes…
http://www.brainyquote.com/quotes/keywords/photographic.html
Knol… A Unit of Knowledge: Lenses for digital SLRs — Lens features explained…
http://knol.google.com/k/lenses-for-digital-slrs-lens-features-explained#
eHow… How to Do Just About Everything: SLR Camera Lenses Explained…
http://www.ehow.com/facts_5182914_slr-camera-lenses-explained.html
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