What's the difference between a varifocal lens and a zoom lens?

Answer 1

A telephoto lens is a camera lens that is typically used for taking photographs of subjects that are a distance away such as a landscape. They are also used for subjects that the photographer can not get close to such as wildlife, and sporting events. A zoom lens allows the photographer to get very close to the subject matter and then zoom in.

Answer 2

Fixed lenses, sometimes called prime or fixed focal length lenses, are often of superior optical quality to zooms because they are of simpler design, can be optimized for a single focal length and have fewer moving parts. They are lighter in weight and usually smaller in size, and one major advantage they have over zooms is that their maximum aperture can be made larger, allowing the lens to gather more light - what we call a "fast" lens, useful in low light. Their optical superiority over zooms is diminishing, however, with some computer designed modern zooms as good or better than their fixed counterparts.

Many cameras used to be sold with what was called a "normal" lens, which was a fixed focal length roughly equal to the diagonal of the film frame. This "normal" focal length gave an angle of view approximately equal to that which the human eye sees sharply. For example, a 4x5-inch camera would have a "normal" lens of 6 inches (150 mm) focal length. A 35 mm camera frame has a diagonal around 43 mm, but the "normal" focal length supplied is usually 50 mm.

Zoom lenses have moving elements inside them which allow them to infinitely vary their focal length through their range, which is a very powerful tool. A very useful general purpose zoom goes from a moderate wide angle to a moderate telephoto, such as a 35-105 mm zoom on a 35 mm camera. When I was working I habitually carried a matched pair of bodies, one with a 35-105 and the other with a 70-210. A 35-105 mm lens can substitute for a "normal" lens with much greater flexibility, but you have to accept greater weight, a smaller maximum aperture and possibly some distortions, often slight "barrel" distortion (straight lines at the frame edges bowing out) at the wide end and "pincushion" (straight lines at the frame edges bowing in) at the long end. Modern computer designs have almost completely eliminated these distortions and aberrations, and modern zoom lenses tend to be lighter as well.

So far as I know, all point-and-shoot digitals come mounted with a moderate wide-to-tele optical zoom. This is distinct from "digital zoom," which just crops the image and can degrade it, sometimes dramatically. If you want to use a lot of telephoto zoom on a point-and-shoot digital, buy a camera with a long optical range for optimum quality.

Answer 3

A "zoom" lens just means that the lens can change its length (e.g. 18-55, or 80-200mm). A telephoto lens is one that make objects look significantly "closer" than they really are (usually defined as anything above 100mm, but this can vary based on the camera model).

So confusingly enough, zoom is actually a feature of a lens, and not a type of lens itself. If you are wanting a lens that make far away things look closer then you want a telephoto lens.

Answer 4

Both varifocal and zoom lenses are built with movable elements that permit changing the effective focal length. A lens might be specified as 3.5-8mm or 6.5-52 mm, meaning the focal length can be adjusted within these ranges.

The key difference between a varifocal and a zoom lens can be explained by thinking about a lens that has been focused on an object at any focal length. A varifocal will need to be refocused whenever the focal length is adjusted; the zoom will stay in focus when the focal length is adjusted (i.e. when "zooming in" or "zooming out").

While this is an advantage in some applications, if a camera is going to be set-up once at an installation and then stay at the same focal length, the varifocal is a smaller lens that will do the job at a much lower cost than the zoom.

Zoom RatioAnother method for describing the range of focal lengths in a varifocal or zoom lens is the zoom ratio. This is ratio of the shortest focal length and longest focal length of the lens. So a lens could be specified as follows:

• 6.5-52mm Zoom or 6.5mm 8x Zoom
• 13-130mm Zoom or 13mm 10x Zoom

The method used to describe a lens is less important than is an understanding of the operating range of a specific lens (for example 3.5 - 8mm), and how the image is affected throughout this range.

Answer 5

A varifocal lens has different focusing points across the plane of the glass (one element). A zoom lens has different optical elements to allow changing of focal length by changing the distances between the optical elements.