Paul Jolly Photography Chapter 28

Difference between lens and digital zoom

These terms are often confused especially on non DSLR cameras.
Lens zoom is where the lens (normally called a zoom lens) can be set to various different focal lengths to produce the amount of the subject included in the picture. Setting the zoom amount uses the whole of the sensor; producing the highest resolution.
When a digital zoom is used the same image is on the sensor but a small amount of the sensor is actually used for recording the picture. This lowers the resolution of the final result. This effect can also be seen when post processing the picture by selecting only part of the recorded image.
The better version is to use the best lens zoom possible to fit the required image and post process the final selection because the selection can be modified to give the actual picture you wish for.
The following pictures were taken with a 1.6 ratio 15 M pixel sensor [Cannon 50D].
The individual pixels are obvious in the 18 mm close up of the bush.

Above left: Picture with 18mm lens. Above right: Picture with 210mm lens

Above left: digital zoom 210 mm equivalent from 18 mm lens
Upper right: close up of bush section of 210 mm lens
Lower right: close up of bush section of 18 mm lens