Optical versus digital zoom

Take a look at the specs of a new digital camera and you are bound to read that it has two kinds of zoom: optical zoom and digital zoom. Today's digital cameras are not complete without these two zoom functions. Some camera makers even overstate them as a selling point.

Zooming in lets you enlarge the image of the subject that you want to capture, as if you are walking closer toward it. Zooming out is like stepping away from the subject.

If you zoom out, the subject will look smaller in your viewfinder, but you can see more of the scene. With the zoom functions, you can zoom in or zoom out without actually moving toward or away from the subject.

In some cameras, you may have two buttons that you can press to achieve the desired picture composition. One may be labeled with a "T" and the other with a "W". The "T" stands for "telephoto" and the "W" for "wide angle". The telephoto is the zoom function while the wide angle, as you already know, allows you to get more of the scene in front of your camera in the picture. Certainly you can achieve one or the other, but not both.

How does the optical zoom work? The subject appears to be closer to you -- and looks bigger in your viewfinder -- because the lens element is pushed away from the charge coupled device (CCD) that captures the projected image and turns it into digital data.

A motor is used to move the lens element forward and backward as you zoom in and out. Clearly, if you do not have a spare battery and you intend to take a lot of pictures, you should avoid zooming in and out too much.

Today, most pocket digital cameras are capable of 3x optical zooming, which means that the lens can move far enough away from the CCD that the image is three times larger than it would be if the lens was at its closest point to the CCD.

Of course, if you use one of those full-fledged, professional cameras like the Canon EOS D10 or Nikon Coolpix you can use a tele-lens, which allows you to achieve much higher zoom capability.

What does the digital zoom do? Digital zooming is possible because the camera uses digital data. What it does is digitally enlarge the image of the subject by increasing the size of the individual pixels (picture elements). You can actually do this in image editing programs such as Microsoft Paint, Adobe Photoshop or CorelPHOTO-PAINT.

The next question is: which is better, optical or digital zoom? Because digital zoom simply makes each pixel larger, the results are not really good. The more you zoom digitally, the more jagged the image will be. Mind you, up till now digital cameras on cell phones can only use digital zoom because the lens has to be fixed due to space limitations.

For the best results, just use the optical zoom. Your pictures will remain as smooth as the original setting. However, because the lens has to be pushed away from the camera, there is a limit to how much you can enlarge the image of your subject with the optical zoom.

When can you use digital zoom? The results of digital zoom may still be acceptable for Web or e-mail. However, if you want to print the image larger than 4x6, the result will be poor if you use digital zoom. Just stick to optical zoom.

This boils down to whether it is important to check the digital zoom capability if you are buying a new digital camera? The answer is not really. You can do digital zoom on your PC or Mac using an image editor. Unfortunately, many camera makers give you the total zoom capability -- for example, "7x (3x optical, 4x digital)". Just ignore the "4x digital". In fact, choose a model that lets you disable the digital zoom capability, because you do not want to accidentally use it. -- Zatni Arbi