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Digital Zoom. What are the benefits ?
It is common knowledge that optical zoom is superior to digital zoom and that when buying a camera optical should always be chosen against digital zoom.
This does not mean however that digital zoom has no benefits, as I hope to show below.
The following discussion applies for A given sized print.
If you set your camera to it's maximum image size then the argument against digital zoom is that regardless of the digital zoom you could always get the same result by cropping later and this is correct but digital zoom may give you the following benefits.
1) About 30% Less storage required for the image.
Sure the image is still saved with the same number of pixels as without digital zoom but there is less information in it.
2) More accurate exposure.
3) More accurate focus.
The automatic exposure and focus will be more accurately set on the part of the image you will keep.
If you leave your camera set to less than it's maximum size image size then you get the benefits above and digital zoom will always result in improved resolution compared with cropping later and in some cases it will result in the same resolution (maximum) that could be obtained by any other method including setting the camera to the maximum image size.
LHS was cropped from a software 2x expanded 640 x 480 with no digital zoom. Note the blur.
MID was cropped from a 640 x 480 with 2x digital zoom.
RHS was cropped from a camera set to it's maximum of 1240 x 960 with no zoom.
When my Canon A30 is set to 640X480 without digital zoom it uses the all of the 1240X960 sensor and then resizes the image to 640X480 for storage. When set to 2x zoom digital zoom the camera uses a 640 x 480 section of the sensors 1240 x 960 pixels and no processing is necessary. This gives the effect of 2x expansion. If digital zoom is not used then to get the same result with software later you would have to select the centre 320X240 section and expand it to 640X480 which would of course result in a degraded image.
My conclusion is that if you have digital zoom you should use it especially if you shoot with the camera set at less than the maximum image size.