Some inexpensive lens makers, for fast production and to cut costs, have little or no quality control. They do not test the lenses after making them. You are the first person to see photographic images made by the lens. So study them carefully. One quick check is to see how sharp the image is when the lens is focused at infinity. A better check can be made by photographing a page of classified newspaper ads taped flat to a wall. Keep the camera's film plane parallel to the wall. Check the results for overall sharpness (watch for edges of the picture that may be out of focus) and uniform exposure (look for edges that may be darker than the center). Make several test exposures at different f/stops.

Telephoto Tips

Sooner or later you’ll consider buying a supplemental lens. Which type of extra lens is best for you? The answer depends on the type of photography you do. For many photographers the most common extra lens is a telephoto lens or a zoom lens. Its focal length, how much it limits the field of view, will vary according to personal preference and purpose. The choice depends on the distance to your subjects and how large you want their images to appear.

Since SLR cameras are designed to be small and convenient, a bulky telephoto lens will alter those features. From 200mm upward, they can get heavy and awkward. Such lenses of great focal length are said to be powerful, extreme, or long telephoto lenses. Often a tripod is needed to support them and keep them steady. Since only a small picture area is encompassed by a lens of great focal length, even slight camera movement will cause a blurred picture. And if hand-held, a camera with a telephoto lens requires a fast shutter speed to avoid this problem. Even then, other support is often needed to get sharp photographic results. Some cameramen use a pistol grip or shoulder brace to help steady their telephoto lenses when making candid pictures.

A telephoto with a fast lens, one that has a wide maximum f/stop, such as f/2.8, is bigger, heavier, and costlier than those telephotos with lens speeds of f/4 or f/5.6 or less. For further comparison it should be mentioned that normal lenses almost always have a larger maximum f/stop opening than telephoto lenses, and thus normal lenses are considered to be faster of the two types. Often you’ll have more of a problem shooting in low light situations with a telephoto lens. That's because its limited maximum f/stop dims the subject you're trying to focus in the viewfinder, and slow shutter speeds are required for correct exposures.

Another consideration with telephoto lenses is that the greater their focal length, the less depth of field. The area of the picture that it is possible to get into sharp focus is reduced as the millimeter of a lens increases. Thus, focusing with a 300mm telephoto lens is more critical, and there is less depth of field possible, than with a 90mm telephoto. Of course, the distance the subject is from the camera and the f/stop used also affect focus and depth of field. The limited depth of field characteristic of telephoto lenses can be used creatively, For instance, such a narrow zone of sharpness enables a photographer to easily isolate and therefore emphasize his subject by keeping an unwanted foreground or background, or both, out of focus.

Although you must use a camera support and/or fast shutter speed to get sharp results, and although you must focus critically because of limited depth of field, telephoto lenses offer many advantages.

The most popular 90mm, 105mm, and l35mm enable portraits to be made without distortion of the subjects features and without getting uncomfortably close. Telephoto lenses also put you where the action is, especially at sports events where fans and photographers are required to keep their distance. Nature photographers count on telephoto lenses to get near subjects without disturbing them, a necessity for bird and wildlife pictures. Travel photographers utilize telephotos to capture informal portraits of people without their being aware of the camera. Distant scenes, or portions of them, can be brought closer for detailed and dramatic effects. Filling your frame with the subject is a basic rule for making an effective picture, and telephoto lenses allow this quite easily. l would advise against purchasing an extremely powerful telephoto lens because its impractical and cumbersome for general photography. You’ll end up too close to most subjects with it its weight and size, plus f/stop and depth of field limitations, as well as cost, make a telephoto lens of great focal length a luxury. There is an inexpensive way to increase focal length and therefore obtain telephoto effect. This is with the use of lens extenders, also called lens converters and teleconverters. These are optical devices inserted between a lens and the camera body which increase the focal length two or three times and thus enlarge the subject image. As such, a 2X extender doubles the focal length of a lens. A 3X extender triples it. Thus a normal 50mm lens becomes a l00mm or 150mm, depending on whether a 2X or 3X extender is used.

However, because focal length is increased, light must travel a greater distance from lens to film, and exposure must be increased accordingly. A through-the-lens light meter accomplishes this. With an external or hand held meter, information for increasing exposure is given with the extenders and should be applied. Generally it indicates that two additional f/stops are required when using a 2X extender, while a wider opening equal to three f/stops is required for 3X extender use. With some cameras, the extenders will couple to the automatic aperture f/stop control. Otherwise, f/stops must be set manually.

One caution: Since the extenders can be fairly inexpensive, the quality of the optics varies. Overall sharpness may be lacking, and the edges of your pictures may be slightly darker than its center area. Nevertheless, if your need for a telephoto is only occasional, extenders can be an inexpensive answer.

Mention must be made of reflex-type telephoto lenses, commonly called mirror lenses and formally called catadioptric lenses. Most are of the greater focal lengths, from 500mm to 2000mm. They were designed to reduce the length, weight, and price of long telephoto lenses. To do this, the image coming into the lens is bounced off a mirror at the rear of the lens to a mirror at the front of the lens.

Because of this unique design, a mirror lens has a fixed aperture, often f/8, that cannot be changed. ln order to get proper exposures, the only thing you can do is adjust the shutter speed control (or use neutral density filters to reduce the intensity of light).

Another limitation of mirror telephoto lenses is that depth of field cannot be controlled because the f/stop is always the same. Also, bright spots in the out-of-focus background often appear as donut-shaped images, which can be appealing or distracting, depending on the picture's subject.

Zoom Lenses

A zoom lens, which allows you to vary focal length, can be very convenient. There are no delays or missed pictures, as may be the case when having to change from one lens to another. Photographers making color slides for projection especially like zoom lenses because they can easily fill the frame with exactly the picture they want to show on the screen. They get closer (zoom in) to or farther (zoom out) from their subjects simply by adjusting the lens.

Other photographers create interesting photographic effects, including one of motion, by zooming the lens in or out during the actual exposure. To allow time for this, the shutter speed must be relatively slow. Early zoom lenses were criticized for producing unsharp images, but the recent generations of computer-designed zooms produce excellent pictures and are a favorite choice of amateur and professional photographers. The main reason for their popularity is that one zoom lens will do the work of several lenses of fixed focal lengths. Unfortunately, many zoom lenses are heavy and bulky compared to those of fixed focal lengths.

Also, comparing the minimum focal length of a zoom lens to a regular lens of that same focal length, the zoom lens usually will have a smaller maximum f/stop opening. This means that in situations where t.he light level is low, some zoom lenses are less useful than lenses of fixed focal lengths. Because of their limited maximum apertures, often f/3.5 to f/4.5, zoom lenses are not as easy to focus in dim light, and slower shutter speeds (or a faster film) must be used for proper exposures. The minimum distance you can get from your subject when using a zoom lens is limited, too, although some zooms feature macro or close focusing capabilities.

Another consideration with some so-called zoom lenses is that they do not maintain their sharpness as you change the focal length. Thus, after zooming in or out to frame your subject, you may have to refocus in order to get the sharpest possible image. Actually, lenses which do not hold their focus are not truly zoom lenses; more accurately, they are termed variable focal length lenses. They must be refocused after every change of focal length. When using quality zoom lenses which stay in focus whenever the focal length is changed, photographers frequently focus while at the greatest focal length because the subject will be larger in the viewfinder and can be focused more critically.

Controls for focusing and changing the focal length of a zoom lens are of two types. A so-called one-touch zoom has a single ring that you push and pull to change the focal length and also twist to focus. A two-touch zoom has two control rings: one you push and pull or twist to adjust the focal length, another you twist to focus. Many photographers prefer one-touch zooms because they can be operated more quickly, although you have to be careful not to inadvertently change the focal length when focusing or twist the ring out of focus when zooming. You avoid such problems with a two-touch zoom, but it takes longer to make focal length and focus adjustments because you have to move your lingers from one ring to another.

I regularly use a one-touch zoom lens of medium focal length, 43-86mm, because it makes composing a picture in my viewfinder very quick and easy. Try out several zoom lenses before deciding which one would be a good investment. They vary considerably in features and prices, according to the manufacturer.

Working with Wide-angle Lenses

The other popular supplemental lenses are of the wide-angle type. They have focal lengths less than a normal lens, often 35mm, 28mm, 24mm, or 21mm, and give a wider field of view than normal lenses. The smaller the length, the wider the view which means the subjects image size will be smaller in the viewfinder and on the print.

Wide angle lenses especially are useful when working in close quarters, such as room interiors or narrow streets. When you cannot move back to include more of your subject, a wide angle lens will do the trick.

Panoramic landscapes also are possible, but the image size of the subject becomes smaller. Towering mountain scenery can be overwhelming when you photograph it, but if shot with an extreme wide angle lens, the result shows smaller mountains and a less impressive picture than you expected. Many travel photographers become disenchanted with wide angle lenses after trying to make dramatic scenic shots.

Distortion with a wide-angle lens is also evident when it is close to the subject. Therefore, portraits of people made with wide-angle lenses are usually unflattering. The portions of a subject closest to the lens are exaggerated. The results can be startling. For example, when taken with an extreme wide angle lens, a picture of a pig's snout can result in the animal looking like an anteater.

A plus factor for wide-angle lenses is that because they have great depth of field, focusing is less critical and sometimes even unnecessary. A 28mm lens, for example, will be in focus from 5 feet to infinity at an average f/stop of f/8. At fl 1 6, the range increases down to 2.5 feet through infinity. For comparison, a normal 50mm lens at f/8 has a depth of field of only 15 feet to infinity.

Wide angle lenses are also smaller and lighter in weight than the telephotos. However, because there lens is designed to take in a great field of view, wide angles often have a front lens element that bulges out. A UV or skylight light filter will help protect it, as well as lens shade that also can block direct sunlight from the lens and avoid flare. Whenever you attach a filter or lens shade to the front of a wide-angle lens, always check in the viewfinder to be sure that it does not obscure the comers of the image.

Because of their short focal length, some extreme wide-angle lenses must be so close to the film that they prevent use of the viewfinder in single lens reflex cameras. The reason is that the cameras mirror must be locked up out of the way, thus cutting off the reflected subject image seen by the photographer. But since focusing and framing is not a problem with such extreme wide-angles, notably the fish eye lens, most photographers adapt to this limitation.

A partial reason is because shooting with extreme wide-angle lenses is an occasional thing. Most photographers save them for a unique shot, too many wide-angle pictures, with their bothersome distortion and tiny subject images, become monotonous if not displeasing. However, the more nominal wide angles, such as the 35mm, 28mm, 24mm, and 21mm, are popular with many cameramen, including news photographers. Any of these would be a good choice if you're considering purchasing a wide-angle lens. Try them out to see which you prefer for the type of photography you do. Make some test shots.

And remember, in addition to exaggeration of close-up subjects, distortion caused by a wide-angle lens also is very noticeable in regard to parallel lines.

Shooting horizontally and level with the subject, any vertical lines will appear straight but if the camera is tilted up, these vertical lines or objects seem to bend inward at the top of the picture. Thus, shooting upward, square building exteriors will narrow at the top. Tilting the camera down tends to bend such lines of objects inward at the bottom of the picture. Corners of rooms also tilt inward or outward depending on the angle of the camera.

Larger view cameras with tilting lenses, and some special cameras, are designed to enable the photographer to prevent such distortion. But unless you use a perspective-correction (PC) lens, it is a problem most wide-angle users with cameras must tolerate. Correction of distorted lines can be accomplished somewhat in the enlarging process, and photographers who make their own prints are less concerned with this problem