Many camera brochures tout digital zoom as being a major selling point, and youâ€™ll often see digital and optical zoom figures added together as a combined magnification as though they were exactly the same thing. They are not.
Optical zoom is provided by the magnification of the image by the camera lens, so the image uses all of the cameraâ€™s CCD to maximum effect. Digital zoom simply takes the centre part of the image from the CCD and digitally enlarges it, so you end up with a much lower resolution image. Itâ€™s like throwing away half your CCD. I always recommend that as soon as you get a new digital camera, go into the set-up menu and turn off digital zoom. If you need to zoom in more than your lens allows, try moving closer to your subject instead.
This picture was taken at the wide-angle setting of a 3x zoom lens. It shows plenty of detail, but what if we want to get a bit closer to the main subject, the cute thatched cottage?
By using the optical zoom, we can increase the magnification of the image, so the cottage fills more of the frame. Because it still uses all of the sensor area there is even more detail visible.
If we use digital zoom instead, all that happens is that a portion of the original image is enlarged, so instead of using the whole sensor area, only about a third of it is used, so although the cottage fills the same area of the frame, it is far less detailed than the optical zoom image. Iâ€™ve exaggerated the effect somewhat in this example, but if you use large amounts of digital zoom this is what you are doing to your pictures.