How do Zoom Lenses Work on Cameras?


The zoom, or magnification, features on a camera are determined by its focal length. The focal length is the distance between the lens and the camera’s sensor. The greater the focal length, the greater the camera’s ability to shoot a clear, close up image from a distance. Conventional film cameras have only optical zoom, while digital cameras may have both optical and digital zoom features.

A camera with a zoom lens.
A camera with a zoom lens.

Optical zoom lenses are usually considered far superior to digital zoom lenses. A camera with an optical zoom feature is much like any conventional camera. The lens is like a telescope that magnifies the subject and then captures the enlarged image. Digital cameras are manufactured with varying optical zoom capabilities. If someone is an avid photographer or has the desire to take quality photographs from afar, then he or she will want to consider the level of optical magnification on a variety of cameras before choosing one.

Many camera companies have developed lightweight cameras with built in zoom lenses for everyday use.
Many camera companies have developed lightweight cameras with built in zoom lenses for everyday use.

Digital zoom is typically not as effective. In addition, using this feature without understanding how it works can produce some very disappointing photographs. Digital zoom works the same way that cropping an image using photo editing software works. For example, if a person has a photograph that he took at a distance and wants to crop it to enlarge some aspect, he would probably notice that it loses its resolution, resulting in a fuzzy or grainy image. A digital zoom lens does the same thing, but as the image is being captured. Therefore, if someone sees a great shot from a distance and uses the digital zoom feature, he is likely to get a poor image.

Why digital zoom is included is a mystery to some, since the same effect can be achieved using software, which can always be corrected if the outcome is poor. Once a photo is taken using this feature, then what is captured is what the photographer gets. Some people feel that the digital version is a marketing technique intended to make one company’s product seem better than another’s without sacrificing the overhead associated with adding a quality optical zoom feature.

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Discussion Comments


@CaithnessCC - I have the same problem, so I rarely use the zoom feature. I'd rather have it available though than use a software package to digitally alter photos. I have never got into Photoshop and all of that.


I've never had a fancy camera, I actually relied on disposables for a long time. Now I have one of the small digital types, which is fine for what I need.

One thing I have noticed is the way the zoom effects the battery life. If I use it a few times the camera runs out of juice!


set the lens to 800. It will get you the best picture resolution.


I have a Pentax K100D SLR. I also have a Sigma Zoom lens marked f=70-210mm. When I attach it to the camera I am asked to set the focal length between 80 --800. What does this mean and how should I set it? Help please.

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