A zoom lens is a lens which can change focal lengths. Some point-and-shoot cameras have a "fixed" lens which does not zoom. This is common in throwaway film cameras and ultra-cheap digital cameras, however most point-and-shoot digital cameras today have zoom lenses and are advertised as "3x" (3 times) or something of the sort. This results in a view at the highest zoom setting where objects appear about 3 times larger than at the lowest zoom setting. Similarly a "5x" (5 times) zoom results in a view at the highest zoom setting where objects appear about 5 times larger than at the lowest zoom setting.
On higher end lenses, such as interchangeable lenses for SLR cameras, the lenses are usually advertised according to the range of focal lengths they cover. A common focal range for the lens included with many SLR cameras is 18-55mm. This equates to approximately 3x zoom (18mm x 3 = 54mm).
A lens which covers a telephoto range (i.e. 70-200mm) is a telephoto zoom, a lens which covers a wide range (i.e. 14-24mm) is a wide zoom and a lens which covers a mid-range (i.e. 24-70mm) is a normal zoom. These terms are somewhat relative. For instance while using a 70-200mm lens one might say by zooming from 200mm back to 100mm they are "zooming wider" even though 100mm is not a wide focal length itself.
Zoom lenses can be convenient with the ability to change focal lengths immediately without the time or trouble spent to change lenses or move around, which could lead to missed shots. However, zoom lenses may encourage the shooter to lazily fiddle with varying focal lengths rather than just "see" and "shoot", getting in the way of that subtle, ephemeral and immediate connection with the picture taking process and camera as extension of the person, which could also lead to missed shots. Too many primes and/or too much zooming could both be signs of a broken workflow and a need for better understanding of one's shooting preferences.
A traditional view says one should begin with a prime lens and learn to move into position and visualize what the lens will see. There are four main problems with this scenario:
- While shooting with a single prime may teach the beginning photographer to visualize what the lens sees, it also handicaps him/her from understanding what other focal lengths see. This leads into the second point...
- Different focal lengths don't merely "zoom" (being "closer" or "farther"), they literally "see" the same scene differently when compared side by side (see Wide & Telephoto). Using a single prime will never make this evident to the shooter.
- Everyone has a differnt eye and different interests. One person may be fascinated with wide or normal shots, while another may prefer long shots. Using a single prime will never present these different possibilities to the beginning photographer, which may inadvertantly affect his/her viewpoint of what he/she "thinks" they like or don't like in exploring their visual identity, and leads into the fourth point...
- If/when the beginning photographer wishes to expand their range of lenses and shooting options, he/she will hardly be any closer to having any idea what focal length to add to his/her "kit" any more than when they first picked up the camera because, again, having a single prime does not educate on the differences between focal lengths. He or she may want a longer lens, but how long? 85mm? 135mm? Without having seen the "look" of these lengths it is difficult to just guess.
Although working with zoom lenses while learning photography presents the possibility of fiddling with the zoom rather than focusing on shooting, it does at least educate on the "look" of differing focal lengths. One always has the option of exploring the traditional approach by leaving the zoom at one setting or taping it to remain at one setting, but learning with a prime never has the option of exploring different focal lengths. After an extended time of shooting (several months to a year), the beginning photographer can look back at his/her favorite shots and see what focal lengths he/she has preferred and then decide whether shooting with primes would be beneficial.
Digital cameras may list both an optical and a digital zoom. Optical zoom is how much a lens can physically zoom, like binoculars. Digital zoom activates when the lens has zoomed as far as it can. At this point the image is not really "zoomed" or "magnified" any further. The camera simply 'blows up" the image as though it were enlarged on a computer, and just like enlarging on a computer there is no more detail to be had, except in some cases when the camera is set to a lower megapixel setting than its maximum. In most cases an image will become blurrier with the use of digital zoom.
As a general rule of thumb digital zoom is something of a marketing gimmick and best to avoid.