A TELEPHOTO LENS is a fixed focal length lens that magnifies the image and a ZOOM LENS is a mechanical lens with the ability to vary its focal length.
What are the benefits or disadvantages are of using a long lens / zoom vs a short lens?
The zoom lens is often a favorite for new photographers because we assume that if we have a zoom with a wide focal range then we will only need one lens. Its usually a choice of economics and ease. Often we don’t always understand the basics of the lenses and what different focal lengths do to the images we create. We typically use a zoom lens just to help us get closer to our subjects without realizing how zooming affects our photo.
I will explain this in just a moment but first its important to mention that a photographers most important tool is his/her own legs. ”Legs” is the industry term for TRIPOD but thats not what I’m referring to here. I mean our actual physical legs attached to our body. If I am able, I prefer to move physically closer or further away from subject to get my desired focal length (to maintain the depth perception I want for the shot). This is of course unless I’m not unable such as shooting wildlife or if I want the affect created by zooming in tight on a subject.
What does zooming do to an image?
Basically, zooming will condense your background and a wider angle lens will keep the background off your subject. Notice the image below. Although the red bottle stays about the same size in the different focal lengths, notice what happens to the background (blue bottle) as the lens gets longer. Each longer focal length the background tends to get larger or come closer to your subject (even thought the subject remains the same size)
Sometimes this effect is desired but other times you want to the background image to appear more realistic. The human eye has a focal length of about 50-55mm (there is some debate about this but for the most part it means our depth perception is similar to a 50mm lens. For example, our human eye would see the images at about the same proportion as the 55 mm image above if we were in a room looking at it).
Portrait photographers usually prefer a focal range from about 85mm-135mm simply because it distorts the background image and if shot at a fast speed (wide aperture such as f/1.2) the background image will be completely blurred (short depth of field) giving emphasis to the subject without a cluttered background.
So, what this teaches us is that if we want to pull our background into the subject (while keeping the same framing of the subject) we simply back up and then zoom our lens in. If we want to push the background off our subject, we shoot at with a shorter lens. If we want our images to look similar to what the human eye sees, then we shoot with a 50-55mm lens (NOTE: In regards to the human eye, this has to do with depth perception and not how wide our eyes can see).
Keep these things in mind before you zoom in on a subject. The zoom is affecting much more than just how close your camera can get to your subject.