PHOTO TALK
Prepared by the staff of Marshall’s Camera
Auburndale, Florida -A17

QUESTION: I am shopping for a really big telephoto lens for my 35mm single lens reflex camera. I read one of your columns about magnification and I need a lens that is 500mm or more in focal length. While looking at lenses I found one that is called a preset lens and it is a lot cheaper than the others. Why is it so much cheaper and is it any good?
ANSWER: A preset lens gets its name from the fact that the user manually sets the size of the aperture before the shutter is operated. In other words the opening in the diagphragm is “preset” by the photographer before the picture is taken. Because it has no automatic diaphragm mechanism the lens is comparatively simple, lightweight, and inexpensive to manufacture. When 35mm SLR cameras were first produced the only lenses available were of the preset type.
The shortcoming of preset lens lies not in their design but in their use. The photographer opens the lens diaphragm to its widest for the best viewing and focusing. After focusing is completed the lens aperture is closed down to the proper size for the chosen shutter speed. Then the picture is taken. My first 35mm SLR camera had a preset lens. About ten percent of the time I would forget to close the lens down before taking the picture. As soon as my finances would permit I bought a camera with an automatic diaphragm so that no mistake was made while taking important pictures. In the first stages of photographic mania every picture that you take is important.
If proper attention is given to design and manufacture the preset lens can create pictures that are among the best. However, if quality is more important than price then the lens will have an automatic diaphragm. If you are on a budget then a good preset lens will do an excellent job.
A note of caution: when shopping for a preset lens make sure that your camera will accept one. Some of the newer entry-level auto focus camera will not use any lens except those that are made specifically for that camera brand. These lens have electrical contacts that exchange information with the camera. Long preset lens are normally made so that an adapter, which has no electrical contacts, is fitted on the lens for use on a camera.
Another type of lens that you might also consider is a mirror lens. This design uses two mirrors to create a folded optical system. A mirror lens is shorter and lighter than the familiar refractor type of the same focal length. Due to the use of mirrors this lens has an aperture that is fixed. The arrangement of the mirrors does not permit a changeable

diaphragm to be used. Another possible drawback to the use of this lens is that out of focus points of light that would normally appear as white dots now show as white circles with dark centers.
One of the things that we have mentioned in other columns is the importance of vibration or shake when using a long telephoto lens. If you are hand holding the camera with a long lens then the numerical value of the shutter speed should be equal to or greater than the focal length of the lens. If the camera is mounted on a sturdy tripod then a cable release should be used so that the camera is not touched by the hand when operated.
With money, planning, and patience that picture of something immensely far away just might be within your reach.
QUESTION: I have a digital camera with a zoom lens that does not bring faraway things close enough. Do they make some kind of lens that I can put on the camera to make the telephoto stronger?
ANSWER: The correct answer depends on your camera. Some digital cameras are made so that auxiliary lens can be attached to the front of the camera. One type of auxiliary lens can increase the longest focal length of the camera lens thereby increasing the overall magnification. Another type of auxiliary lens can decrease the shortest focal length of the camera lens thereby providing a wider field of view than what is available with the camera lens alone.
These lenses are usually attached to the camera by the use of an adapter tube that is fastened to the body of the camera. On most digital cameras the lens is retracted into the body when the camera is turned off and then protrudes when the camera is turned on. The length of the adapter tube is matched to the camera so that when the camera lens protrudes it just misses hitting the back of the auxiliary lens.
Auxiliary lens that can be used on digital cameras are available from a variety of sources. The camera manufacturer usually will have a selection available. However auxiliary lens were in use long before digital cameras came on the scene and many of these earlier designs appear to give good results. The appealing thing about digital cameras is that attachment of the lens to the camera is all that is needed to determine whether the lens will or will not meet your standard of excellence.
If an auxiliary lens is used then the optical viewfinder on a camera so equipped can no longer be used and the view given by the LCD screen has to be relied upon solely for composing the picture. This can cause some problems when bright sunlight threatens to wash out the viewing screen. Hoods to fit the LCD screen are available for use in bright light conditions on some camera models.
Check MarshallsCamera.com for the Beginning Photography course covering both 35mm and digital camera use.
Copyright 2004 Marshall Ledbetter