What's the difference between Digital and Optical zoom ??

Optical zoom uses the camera lens to enlarge the subject in the frame, and it
works in the same way as a film camera. There is no loss of quality from using optical zoom.
Digital zoom is quite different. Many cameras magnify the photo by multiplying
one pixel into two, three or more pixels.
They interpret the image and basically make the area in the middle larger by interpolation.
This means that a lower resolution photograph is used to achieve the zoom,
and the camera cheats to make it look bigger.
By using the digital zoom you are reducing the quality of your output: you would get a better result by
taking a photograph without digital zoom and cropping on the PC later.