The zoom effect in a digital camera is similar to, yet different, from that of a conventional camera. In a conventional camera the zoom effect is the result of optics. It brings distant subjects closer.
However, in a digital camera there are two kinds of ‘zooms’. The first is similar to that of a conventional camera and is known as the optical zoom. The second is the digital zoom, and is more interesting. It ‘simulates’ optical zoom by enlarging a portion of the image -- that is the digital zoom selects a portion of the photograph and blows it up.
The zoom effect should not be confused with photo editing, where an image editing software is used to crop and blow a picture on a computer screen. Another misconception associated with digital zoom is that it is very handy in capturing long distance images. Nothing can be more misleading. It is optical zoom that matters more in a digital camera.
In fact, today the digital camera manufacturers have started using a new term – total zoom. This term only confuses the customer for there is nothing like total zoom. At best, it can be used to indicate the fact that a digital camera has both kinds of zoom – optical zoom and digital zoom.
Another zoom effect that has been developed recently is the “smart zoom". This zoom maintains the image quality by avoiding interpolation of the image. However, smart zoom works only if you select an image smaller than the full available image size.
The zoom that should be used for comparing cameras is optical zoom, and not digital zoom or total zoom. A camera’s quality depends upon the value of optical zoom; a camera with higher optical zoom is better than a camera with lower optical zoom.
Sometimes optical zoom is compared to resolution while buying a digital camera. Nothing can be more absurd. These are two different values and have no common link. Resolution is used to indicate the number of pixels in an image while optical zoom is used to define the lens power. It can neither increase nor decrease the resolution.
There is also a tendency today to disable digital zoom. Some photographers prefer to crop and enlarge an image on a computer screen. They don’t trust the camera to do it for them. This is not a good practice because it reduces the effectiveness of your camera.