Prime lenses for your 35mm SLR system
Aug 30 '01
The Bottom Line Choose each lens according to its capabilities, your needs and your budget.
Single lens reflex (SLR) cameras have interchangeable lenses, thereby opening the door to many different photographic opportunities. This article is about choosing prime (fixed focal length) lenses for an SLR system, rather than zooms.
Why primes? Because, despite the obvious convenience of zoom lenses for general use, prime lenses also have an important role to play. There are some excellent zoom lenses on the market these days, that can probably meet 80% or more of our photographic needs; however, prime lenses are better able to meet the remaining 20%.
It is easier to design a good quality prime lens than a zoom, with the result that primes generally have wider maximum apertures, give higher contrast, cause less flare and are freer from distortion than zooms. Some examples of the types of photography better served by using prime lenses are:
* shooting in low available light, requiring a wider
aperture than a zoom lens can give
* taking pictures against the light, where a zoom lens
would be more prone to flare
* some sports and wildlife photography, requiring a lens of
very long focal length (minimum 400mm) and exceptional
optical quality
* true macro photography; some zoom lenses have a "macro"
setting but do not really fit the bill for serious
macro work
* architectural photography where a shift lens is called
for
* any time the quality of the image is of paramount
importance.
This article discusses prime lenses in the categories of:
- ultra-wide angle
- medium-wide angle
- standard
- short telephoto
- medium telephoto
- super-telephoto and
- special purpose lenses.
ULTRA-WIDE ANGLE LENSES
Lenses in this category have focal lengths of around 15mm to 21mm. The lenses with the shortest focal lengths usually have bulging front elements, to which filters cannot really be attached and which prevent the use of a shade or lens cap. Some have a built-in filter turret which enables the selection of various coloured and neutral filters. Rectilinear lenses are discussed here, designed not to distort the image like a fisheye lens would (see special purpose lenses).
Great depth of field is one important feature of ultra-wides, giving sharp images over a great range of distances and making precise focus unnecessary in many situations. They are mainly used for interiors of buildings, some landscapes and in situations where the photographer wants to create a feeling of being in the thick of things. They are not generally suitable for portraits, because they cause features closer to the lens to be magnified: people appear to have huge chins, noses or foreheads.
Ultra-wides are difficult to use successfully, even for an experienced photographer, because they demand careful subject selection and composition. The image in the viewfinder is rather like looking through the wrong end of a telescope. There is a great deal of foreground and the background looks very small and distant.
The angle of view is from around 120 degrees to 90 degrees for lenses in this category. It is easy include unwanted objects in the view, such as your own feet. Tilting the camera causes converging verticals, making buildings appear to be leaning. Also, the lens can take in too much of the sky, which can easily fool the camera's metering system into under-exposing.
Ultra-wides can be used to create spectacular landscape pictures, giving a dramatic sense of great space, but it is important to have a suitable subject, such as a tree or architectural feature, in the foreground.
Finally, ultra-wides tend to be big, heavy and expensive. Because of their protruding front element, the shortest focal length lenses are difficult to transport safely and require careful handling. An ultra-wide angle lens should be selected only after careful thought. If possible, rent or borrow one for a weekend and try it out before deciding to buy.
MEDIUM-WIDE ANGLE LENSES
In this category are lenses of focal length in the range 24mm to 35mm. Maximum aperture is usually f/2.8 or f/4. They are quite compact, lightweight and not especially expensive.
Many people find these lenses give a natural-looking image, are much less of a challenge to use than the ultra-wides and are very useful. They are used for landscapes where wide coverage is needed, building interiors, architectural photography where it is not possible to shoot from a distance, crowd scenes, group photographs and street scenes. The 24mm and 28mm lenses are not particularly good for portraits, since they give unnatural magnification to features, although not as much as with an ultra-wide angle.
The penalty for tilting the lens is not as severe as with an ultra-wide but it is still necessary to guard against converging verticals. In landscapes it is preferable to have some suitable subject in the foreground. Be aware that a hilly or mountainous landscape may appear less dramatic in the photo than it was in real life when using a wide-angle lens.
Many people choose the 35mm focal length as their normal lens because it is easy to use and gives a natural-looking view without excessive wide-angle characteristics. Many fixed lens point-and-shoot 35mm cameras have a 35mm focal length lens for this reason.
STANDARD LENSES
The range of focal lengths for lenses in this category is about 40mm to 60mm, 50mm being the most common. The standard lens provides an angle of view of about 45 degrees, giving a breadth of view roughly equal to the in-focus portion of the human angle of vision. The magnification is such that the size of the image is about the same as seen with the naked eye.
It is relatively easy to design standard lenses with wide apertures and good optical performance, so they tend to be the fastest, most compact, lightest and least expensive lenses available. Maximum aperture is typically f/1.4 or f/1.8, which is useful for photography in low available light.
Beginners are often encouraged to start off using a standard lens, because it's relatively easy to compose the picture and the wide maximum aperture means that a fast shutter speeds can be used to minimize the effects of camera shake. Standard lenses serve many purposes well, including street photography, landscapes, architectural photography from a reasonable distance, full-length portraits and low available light photography.
SHORT TELEPHOTO LENSES
Lenses in the short telephoto category have focal lengths in the range 75mm to 135mm. They are usually quite compact, lightweight and not too expensive. Maximum aperture is typically f/2 or f/2.8. The best and most expensive lenses are of apochromatic design, which means that light at three different wavelengths is brought to the same focus, instead of the usual two. This makes a visible difference to the sharpness of the image, particularly at telephoto focal lengths.
These are the most popular lenses for half-length, head and shoulders or head only portraits. They compress distance slightly and, because of this, tend to give a pleasing perspective to the face. They are also good for isolating the subject from its background, since they have quite shallow depth of field at wider apertures. This is often important in portrait photography.
Other common uses of short telephoto lenses are landscape photography, where one particular portion of the field of view needs to be isolated; and architectural photography, from a distance or to isolate some architectural or sculptural feature.
MEDIUM TELEPHOTO LENSES
This category includes lenses with focal lengths in the range of 180mm to 360mm. Typical maximum aperture is f/2.8 or f/4. Again, the best and most expensive lenses are of apochromatic design. Medium telephoto lenses can be quite large and heavy, especially those with wide maximum aperture, but are generally hand-holdable under bright conditions and/or with fast film. However, these lenses are best used with a tripod if there is any choice.
Medium telephoto lenses give a marked compression of distance, making far objects seem close together. Depth of field is very shallow at wider apertures. They are used for landscape photography, where compression of the features of the view can enhance its attractiveness, or to isolate a particular feature such as a cliff face or mountain peak. They are also used for animal photography at medium distance, such as in a safari park or zoo.
They are not usually selected for sports or wildlife photography, since the image of the subject would be too small.
SUPER-TELEPHOTO LENSES
This category includes lenses from 400mm to 1000mm or above. These are specialized lenses used for photographing subjects at great distance, such as wildlife and some types of sports. They are expensive and heavy. Some lenses in this category are able to be dismantled for easier transportation. Many are sold with a case for this purpose.
The use of a tripod or shoulder-stock is pretty well mandated. The tripod is used to support the lens, rather than the camera, although it can be necessary to support both. Maximum aperture is usually in the range f/4 to f/8. Depth of field is very shallow and precise focusing is important. Compression of distance with these lenses is extreme. They often have a built-in filter turret or drawer in the vicinity of the iris diaphragm, since it is impractical to fit filters in front of the lens.
Super-telephotos constitute a considerable investment and are difficult to transport. However, if you need to photograph wildlife or sports where the action can be a long way from the camera, then this it the type of lens you need.
One special type of lens in this category is the mirror, or catadioptric, lens. This uses a concave mirror to provide the magnification, with refractive elements to focus the image. It has a fixed aperture, usually f/8. Out-of-focus highlights in the field of view appear doughnut shaped, because of the annular shape of the mirror. These lenses are quite a lot shorter and lighter than their refractive equivalents, making them easier to transport; however, their fixed aperture restricts their flexibility.
SPECIAL PURPOSE LENSES
MACRO lenses are specially corrected for close focusing and have a flat image field. When used alone, a macro lens can give a 1:1 or 1:2 image-to-subject ratio; with extension tubes or bellows, much higher ratios can be attained. They are used to photograph flowers, insects, details of machinery and other small subjects needing high magnification. Focal lengths depend on the purpose of the lens but the most fall in the standard or short telephoto range.
A longer focal length allows for a greater camera-to-subject distance, which is usually only a few centimetres anyway. This can make for easier photography of live creatures. Depth of field becomes critical at such short distances and it is normally necessary to stop these lenses down to f/11 or smaller.
The excellent performance of some macro lenses at normal distances makes them good candidates for general use, too, although they are rather more bulky and usually a little slower (smaller maximum aperture) than conventional lenses of the same focal length.
FISHEYE lenses are of short focal length, from about 8mm to 16mm, and provide an image with extreme barrel distortion, like one sees in a convex mirror. Only straight lines that pass through the centre of the lens appear straight in the image; lines elsewhere are bowed outwards - "barrel" distortion. Apart from this, they have the characteristics of other ultra-wide angle lenses.
The usefulness of fisheye lenses is very restricted in practice. Some people buy them for their novelty value but quickly tire of using them. Used imaginatively, however, they can be very effective in providing an unusual perspective.
SHIFT or perspective correction lenses are sometimes necessary, in architectural photography, to avoid converging verticals. These medium-wide angle lenses allow the lens to be shifted along horizontal and vertical axes so that the camera does not have to be tilted, for instance, to photograph a nearby tall building. They are able to do this because they project an image that covers a much wider circle than normal for a lens of that focal length. Since the image on the film is much smaller than the real building, a small amount of shift makes a big difference.
Shift lenses are fairly bulky and expensive. They do not couple to the camera's aperture sensing and control cams, so they have to be used stopped down to the working aperture. For these reasons, they are not a particularly useful substitute for a conventional wide-angle lens for general photography.
EXTENDERS or teleconverters can add flexibility to your lens line-up, providing a relatively inexpensive way of attaining long focal lengths. Some image quality is lost, although this may be slight enough to be ignored in practice. Extenders are used with lenses of focal length 50mm and above.
A 2x extender used with a 100mm, f/2.8 lens would result in a focal length of 200mm. However, the effective maximum aperture would be only f/5.6, because two f-stops are lost with a 2x extender. Substituting a 1.4x extender would result in a focal length of 140mm and maximum aperture of f/4.
It is important to be aware that not all lens/extender combinations are possible and that physical damage can result from the incorrect application of extenders.
CONCLUSION
Here are some tips that I hope you will find useful for selecting prime lenses:
* plan carefully the range of focal lengths that you need
to buy, based on the photography you intend to pursue
* select lenses that are placed at sensible intervals in
your required range; for example, when selecting lenses
to cover ultra- to medium-wide angles, you might find that
a set comprising 18mm, 24mm, 35mm will provide a useful
choice of lenses
* when it comes to deciding what maximum aperture you need
for a particular focal length, remember that the faster
the lens, the more it will cost and the bigger it will be;
to keep down cost and size, choose only what you really
need
* don't forget to consider the mechanical aspects of
lens quality when making your choice, especially if you
anticipate that the lens may be subject to heavy use
and/or unfavourable conditions
* if you have a project that needs a special, expensive
lens that you don't already own and are not likely to
need in the long term, you might be able to rent it
* don't expect to find a good cheap lens!
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