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, etc.). 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.

 

Optical Zoom vs. Resolution

 

What about optical zoom vs. resolution? Sigh! Now y'all know that we cannot and should not be comparing apples 'n oranges, but we still try. The question I often read about goes something like this: "Which is better: 2 megapixels resolution with 3x optical zoom or 3 megapixels resolution with 2x optical zoom?"

 

The megapixels resolution of a digital camera can be thought of as the number of pixels available to capture an image. With a 2 megapixels camera, you have 2 million pixels to record an image. With a 3 megapixels camera, you have 1 million extra pixels to record the same image -- in other words, you are able to capture the image in more detail.

 

Whether you zoom or not does not affect how many pixels are used to capture the image. So, zoomed at its maximum, a 2 megapixels 3x optical zoom digital camera will still have captured a 2 million pixels image. Likewise, a 3 megapixels 2x optical zoom digital camera will always capture a 3 million pixels image.

 

The real question behind the question is, "So now if I use digital zoom to zoom in with the 3 megapixels camera and simulate a total zoom of 3x, will the resultant image quality be less, the same, or still better than the one I captured with the 2 megapixels 3x optical zoom camera?" You follow so far?

 

With a 2 megapixels digital camera, you can make good 4x6 in. prints, and maybe even 5x7 in. prints. With a 3 megapixels digital camera, you can make good 8x10 in. prints. So, as far as image quality is concerned, the 3 megapixels camera is better. Unless you are always going to take pictures at max. zoom, the 3MP camera is better because at 2x optical zoom and less, it is always capturing images with more detail than the 2MP camera.

 

What we are really trying to say is this: do not compare. You've got to decide what is more important to you: resolution or optical zoom? If the answer is both, then find a digital camera that has both. It's that simple. If it's outside your pocketbook range, then choose a digital camera for what is more important to you.

 

To repeat, we do not compare optical zoom with megapixel resolution because optical zoom is not megapixel resolution-dependent. That is, the resolution of your final image does not change no matter how much you zoom in. If your digital camera is 5MP and has a 12x optical zoom lens with focal length of, say, 30-360mm, then at 30mm, your image is 5MP and at 360mm, it is still 5MP. With digital zoom/enlargement, the megapixel resolution decreases as you "zoom" in digitally (the premise behind Smart Zoom from Sony and Safe Zoom from Canon, see below); if you try to bring the cropped image back to the same 5MP size, then there is pixels interpolation and the resulting image suffers in quality.

 

We always disable digital zoom in camera, choosing to do our own cropping and enlarging in an image editing software.

 

Optical vs. digital zoom? There is no contest. Only optical zoom matters when selecting a digital camera.