Autofocus Lenses

In its infancy in 1978, autofocusing was limited to cameras with non removable lenses. Then the feature became available for 35mm single lens reflex cameras. At first the SLRs with autofocus capability required a particular lens, like the Pentax ME-F camera that was designed for use with the Pentax f/2.8 35-70mm autofocus zoom. Later, Nikon improved autofocus possibilities with its F3AF model and a special autofocus teleconverter that accepts 15 regular Nikon lenses from 28mm wide angle to 300mm telephoto for automatic focusing by the camera. In 1984 another giant step was made by an innovative lens maker, Vivitar, with the introduction of its f/5 200mm autofocus lens, which can be attached to most popular 35mm SLR cameras.

Despite considerable progress in a short span of time, autofocus lenses for 35mm single lens reflex cameras still face some hurdles before photographers adopt them with enthusiasm. Common complaints have been that autofocus lenses can be fooled by subjects that are too dark or too bright or that have too little or too much detail. Slow focusing response time has been another concern. With accurate and quick autofocusing as their ultimate goals, manufacturers of the new generations of autofocus lenses must also try to reduce the extra size, weight, and cost of such lenses in order to guarantee their future popularity.

Macro Lenses

Macro lenses are dual-purpose lenses because they can be used for making close ups in addition to their regular role as a normal lens or telephoto lens or zoom lens. Some manufacturers call their macro lenses micro or close focus lenses. Close-up photography is very convenient because you don't have to bother with additional close up lenses or other attachments. Many macro lenses will even produce life size images, but the addition of an extension tube may be required in order to permit one-to-one (1:1) reproduction ratios.

Before purchase, study technical literature about any specific macro lens to see how close you can focus and the maximum reproduction ratio the lens will achieve. Since focus is critical in close-up work, a macro lens with a minimum aperture of f/22 or f/32 is advantageous because the smaller the lens opening, the greater the depth of field. lf you do close-up photography infrequently, a drawback to having a macro lens, instead of a normal, telephoto, or zoom lens, is that its maximum aperture is usually one or two f/stops less than the widest lens opening available on a regular nonmacro lens.

Close-up Lens Concerns

Close-up lenses are another category of supplemental lenses. They are especially popular with photographers who like full-frame pictures of small subject’s flowers and insects are examples. They also are useful for copying, although the image may not be uniformly sharp unless a small f/stop is used.

They allow the camera to get closer to the subject than usual. These close-up lenses screw or snap on a normal, telephoto, or zoom lens; using them requires no increase in exposure. The main concern with close up lenses is the lack of depth of field. The closer the subject, the more critical focus becomes. For this reason, and that of parallax errors, single lens reflex cameras are preferred to range finder cameras for making close-ups. With an SLR you see what the lens sees, and you can frame and focus accordingly. With a rangefinder camera, focusing and framing cannot be done visually in the usual manner. Distances are measured with a ruler and the lens focusing scale is set according to the strength or power of the close-up lens being added.

The strength or power of a close-up lens is referred to as its diopter and is indicated by a plus sign with a number, such as + 2. The higher-this number, the closer you can get to your subject and thus the larger the image size which results on the film. How close you can get to your subject depends on the close-up lens being used. The following chart indicates focusing ranges ac- cording to lens diopters.

The most popular set of such lenses is of three powers, + 1, +2, and + 4. They can be used alone or two in combination. For example, a + 1 and a +4 equal a diopter of + 5. Put the strongest of the two lenses closest to the camera lens. The maximum strength of a single close-up lens is + 10. Some zoom-type close-up lenses are available, offering a range of powers from + 3 to + 7 diopters, for example. Such variable focal length close-up lenses can be adjusted to vary magnification and thus alter the subjects image size with ease. After each adjustment, however, these lenses must be refocused.

To fit correctly, close-up lenses should be purchased according to the millimeter of your lens. These screw onto the lens directly. Others come in series numbers to fit into a lens adapter. These adapters screw in or snap on the camera lens to accommodate close-up lenses or filters. Close up lens series numbers range from 4 through 9. Do not confuse them with the identifying numbers some camera manufacturers have given to their close-up lenses.

Before buying a close-up lens, check that it fits on your camera.

Manufacturers of close-up lenses provide a chart to indicate where to set the distance on the camera lens focusing scale, depending on how far the close-up lens is from the subject. Then the subject will be sharply focused.

The size of the resulting picture area, the field of view, also is indicated. A depth of field scale should accompany the close-up lens instructions, too. Remember, use of close-up lenses requires no increase in exposure. At close range to a subject, the rangefinder camera's viewfinder may not see what the film's lens does. Parallax error results. Unless his rangefinder camera features automatic parallax correction, the cameraman must disregard the viewfinder and frame his picture in another way. This is often a home made device that extends from the close-up lens to the subject. It can be made of wire fastened to the camera, or a cardboard diagram can be held from the lens to the subject during framing. A tripod helps keep the distance and framing position exact. Some rangefinder cameras, however, do have an attachment for use with close-up lenses that mounts on the viewfinder and gives the photographer visual correction for focusing, field of view, and parallax.

By far, however, the SLR camera is the most convenient and accurate to use with close-up lenses. With the close-up lens in position, you simply focus and frame through the lens as you would normally. Built in light meters make direct and correct exposure readings through the attached lens, too.

The sharpness of these supplemental lenses is important because in working so close to the subject the depth of field is very limited. For this reason a smaller f/stop is always recommended. This usually means a slower shutter speed, and thus some support is needed to keep the camera steady as in a tripod. Such a support is also valuable when making close-ups to help maintain lens to subject distance after focusing.

With or without support, flash will provide extra light so a faster shutter speed or smaller f/stop can be used. Light from an electronic flash is bright but brief and generally will stop any movement of the subject. For extreme close-ups with no-shadow results, ring lights, special electronic flash units which encircle the lens, are available.

An interesting and inexpensive way to get close-ups is to use your normal or wide angle SLR camera lens in reverse position. Many photographers have made emergency close-up shots by removing their nomnal or wide angle lens and turning it end for end. This allows a decrease in the distance between subject and camera, and thus an increase in the subject’s image size on the final print.

For instance, a normal 50mm lens that can be focused in the regular manner only as close as 18 inches from film plane to subject will cover a subject area measuring 6% at 10 inches. Reversing that lens allows the photographer to get his film just 8 inches from the subject. And now the subject area included by the lens is only 1.5 x 2 inches. Thus, by reversing his lens the photographer has increased the image size of his subject five times.

Special lens reverser rings are available for some cameras in order to mount the lens in reversed position. Without one, you'll have to hold the lens in place. Use your fingers to make as great a light-tight collar as possible between the lens and camera body. Prefocus at infinity, and then move your head and camera slowly back and forth to bring the subject into focus through the viewfinder of your SLR. Try lt.

Of course, the automatic exposure control of the lens will not work when it is in reversed position. The f/stop must be actuated manually for the proper exposure. The built-in light meters of SLR cameras will give an accurate reading as you turn the f/stop control ring. The picture you see through the viewfinder will get dimmer as the lens is stopped down. Despite what may seem a strange procedure, reversing a normal or wide-angle lens is a good way to make occasional quick close ups.

Non optical attachments also allow more extreme close-ups to be made. The least expensive and most common are extension tubes. These metal rings are placed between the normal lens and the camera body. In this way the camera lens is moved away from the film, allowing you to get closer to your subject and increase its image size on the film. A close-up lens can also be extended for even greater magnification.

Extension bellows act on the same principle. These flexible extension devices fit between the camera body and its lens, too. By turning knobs the bellows can easily be extended to increase the subject’s image size. Although far more versatile than extension tubes, bellows are more expensive and cumbersome.

With either one, exposure is affected because the lens is moved farther from the camera. Since the light has to travel a greater distance from the lens, a longer exposure is needed. Built-in through-the-lens meters will compensate. Otherwise you have to increase the exposure according to how great the lens distance is.

Charts come with extension bellows and tubes and give the increased exposure factors for the degree of magnification with the lens being used. Some extension bellows and extension tubes allow use of the camera's automatic lens aperture control. Otherwise, f/stops must be set manually for correct exposures.