Optical vs. Digital Zoom
More and more camera manufacturers are choosing to label their digital cameras with the total (optical x digital) zoom. This is an unfortunate development and only serves to confuse consumers.
Most people who have used a 35mm camera or an APS camera are aware of only optical zoom. Optical zoom uses the optics (lens) of the camera to bring the subject closer. Digital zoom is an invention of digital video cameras. It is not uncommon to see digital videocams with 300x digital zoom.
For our purpose, digital zoom is not really zoom, in the strictest definition of the term. What digital zoom does is enlarge a portion of the image, thus 'simulating' optical zoom. In other words, the camera crops a portion of the image and then enlarges it back to size. In so doing, you lose image quality. If you've been regularly using digital zoom and wondered why your pictures did not look that great, now you know.
Is digital zoom therefore all bad? No, not at all. It's a feature that you might want in your digital camera (in fact, all digital cameras include some digital zoom, so you can't really avoid it), especially if you don't care about using (or don't know how to use) an image editing software. So, as far as digital zoom is concerned, you can do it in camera or you can do it afterwards in an image editing software. Any cropping and enlarging can be done in an image editing software, such as Photoshop.
So, when a digital camera is advertised with 3x digital zoom, no big deal. You can achieve the same 3x (and in fact as much as you want) digital zoom effect in an image editing software. The advantage of doing it later is that you can then decide exactly which portion to crop and how much to enlarge (3x, 4x, ...). If you do it in camera, image quality is irreversibly lost.
Someone in a digital camera forum once mentioned that he uses digital zoom because it might mean the difference between capturing a great shot or not at all. Umm, let's think about this a bit. True, if by zooming digitally in camera you get to see what your subject is doing and thus can capture the shot at the right moment. Not quite true, if it's something like a landscape shot, and the mountains ain't going nowhere fast, because you can achieve the same cropping and enlarging effect after the fact in your image editing software. So, it's really up to you, if you know what you're doing.
What, therefore is the rule of thumb, when it comes to using zoom? Here it is: Always use optical zoom. When buying a camera, choose one that warns you that you are about to use digital zoom or that allows you to disable digital zoom (most do). If you do use digital zoom, use it only if it does not appreciably impact your image quality. If you rarely print past 4x6 in. photos, digital zoom may not adversely affect you.
When comparing cameras, you should always use optical zoom. There is no point in comparing digital zoom with digital zoom or optical zoom with total zoom. Always compare optical zoom with optical zoom.
Do not mistake Digital vs. Optical Zoom
Another place to make a serious mistake is in the zoom capability of the camera. Digital zoom is accomplished simply by throwing away pixels. To get 2X magnification, they just use one-FOURTH of the pixels available, and ignore the rest. Voila, the picture is zoomed in. This is free for the maker to provide, since it requires no moving parts. But you've also lost 3/4 of your resolution! Now your crisp 5 by 7 is at best a pretty good 2.5-inch photo. Optical zoom allows you to frame the picture without almost no loss in resolution, limited only by the quality of the lenses. Don't even consider a camera without optical zoom. Be sure the camera can optically zoom at least 2X, and more would be even better.
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