What is zoom?

Sometimes when you take a photo you need to focus on one area in the picture frame. For example when you take a portrait photo you want to make sure the object's face fills the photo frame while when you take a group photo you want to make sure everybody is in the photo frame.

In to focus on that one area in the photo frame you can either physically move closer to the objects or use the camera's zoom feature. When using the zoom feature the camera (mechanically when applying an optical zoon or electronically when applying a digital zoom) enlarges that area to fit the full picture frame.

There are two types of zoomoptical and digital (in older film cameras the only zoom option was optical). We will try to explain the differences between the two.

How does optical zoon work?

Optical zoom works by physically moving the camera's lenses and changing the focal length. By changing the focal length you can make objects appear bigger and fit the full photo frame.

When satisfied with the zoom position you can shoot the photo by simply applying the shutter button.

How does digital zoom work?

With digital zoom you actually use built-in software in the camera to define a portion of the photo which you are interested in. Once chosen the software crops the rest of the photo and enlarges the area you chose to fit the complete photo frame.

The process of enlarging the zoomed area is also known as extrapolation. The camera software needs to calculate new values for the pixels that were cropped in order to result in a full frame photo. The downside of this digital process is that the enlarged photo quality is lower than the original photo taken.

It is easy to understand the quality loss using an example. Lets assume that you have a 2MP (2 megapixels) camera. You point the camera and decide that you want to zoom in 2X. You run the digital zoom software and choose a 2X zoom. To accomplish this zoom the camera crops half of the photo and enlarges the other half to create a 2X zoom effect. In the process a 1MP area is discarded (the half that is cropped). The other 1MP area is enlarged in a process that copies every pixel once to generate a 2MP photo. Although the new photo seems to include 2MP it really includes only 1MP of information that was copied once. The result is a photo with a quality equivalent to a 1MP photo.

If you have used a 4X digital zoom in this example the result would have been a photo with an equivalent quality of a 0.5MP camera (the zoom area is 1/4 of the frame3/4 of the frame would be discarded and the rest 1/4 would be copied three times to fill the frame).

Digital zoom significantly reduces the quality of the photo. If your camera does not include digital zoom you can always shoot the photo without zooming and then use a PC photo editing software to crop a portion of it and enlarge the rest. In fact using PC software is always the preferred method to built-in digital zoom since it allows you to try different zoom sizes, different zoom areas and different zoom algorithms while not losing the original photo.

So which one is better?

Optical zoom is superior to digital zoom. In fact from a practical point of view digital zoom should not be considered zoom at all. It is always better to apply digital zoom on a PC at a later time rather then when taking the photo using the camera's built-in digital zoom. When using a PC different sizes can be used and different zoom algorithms that can result in better qualities.

Know your camera's zoom

Some manufacturers claim the maximum zoom figure their cameras support without specifying if it is optical or digital zoom. This information is confusing as many consumers do not understand the difference between the two. For example if a camera supports a 5X optical zoom and 10X digital zoom advertising the camera as a "10X zoom camera" is confusing10X digital zoom can be done with any camera using simple PC software.

When buying a camera always make sure that you know what the optical zoom figure is and that it meets your needs. Ignore the digital zoom figure as it does not mean much and can not compensate for a camera with poor optical zoom.