Before making a comparison it is important to discuss the significance of the subject matter, in this case the zoom. Well a zoom lens has more than a few portable glass components inside it. By adjusting these components, the focal length of the lens can be altered. Modifying the focal length alters the view distance as well as reduces the field of view, thereby making the projected image to appear larger.
It must me noted that both the optical zoom and the digital zoom are components that are used to magnify an image, but they work in fundamentally different principles and acquiesces drastically different results. In general, optical zooms always produce a far finer and advanced image than digital zoom.
Looking at the functions of these zooms, in digital cameras that offer optical zooms function the same way similar to a zoom lens of a conventional analog camera. A conventional lens works by accumulating light rays that are projected over a portion of a film, and in this case of a digital camera optical sensor. The distance of the lens from the focus point where all of the light rays converge is known as the focal length of the lens. Unlike the optical zoom, the digital zoom works by ranging the pixels in the ultimate image after the image has been captured. The fact remains that the same number of pixels are collected when the photograph is magnified. The only thing that alters is the light rays that are projected over the optical sensors to figure out those pixels.
It is a common intuition that optical lenses are far better than the digital zooms. The reason is that the digital camera zooms are more prone towards computer applications in them rather than mostly human interactions and expertise. Yet, it also remains a fact that beginner photographers find it more useful to handle a digital zoom and also its computer friendly nature. There the computer does the intricate tasks of finding some levelheaded approximation of colors that pixel might take up as it had captured the images or photographs. Many algorithms are existent in this area, but perhaps the most abundantly used algorithm involves looking at the pixels that are quite nearly like neighbors and come up with a kind of an average. Anyways the process remains too complicated and its end result is what the digital zoom users are interested in.
Thus the ultimate truth remains that it is useless to compare digital zooms with optical zooms. Perhaps it is more logical to compare optical zoom with optical zoom and digital zoom with digital zoom. Both these two types of zooms, the optical as well as the digital, have some good and bad qualities. Both of them have some extra features and preferences over the other. And thus it is not wise to compare them, even though a comparison may exist. The efforts would then perhaps look like comparing oranges with apples!