Canon A300: What resolution when zoom in 5x? Calculation?

Can someone explain this to me? when you zoom in at 5.1x with a 3.1 mega
pixel camera, what resolution do you get?
I am thinking of buying canon A300, and wanted to know what resolution I
would get when using the digital zoom. Calculation 3.1 divided by 5.1
= 0.63 mega pixels? Is that correct calculation?

 

I don't think so. The 5.1x is in both width and height so the area
magnification is 5.1 x 5.1 = 26.01. So you would get 3.1/26.01 = 0.119MP.
Note also that the camera would still save the image at the current setting
for resolution by interpolating pixels. So at highest resolution you would
still get a 3.1MP image - it just wouldn't look very good!

Some Sony cameras have a so-called "smart zoom" which you can only use at
lower resolution settings. This effectively just crops the centre portion of
a full resolution image and shouldn't need to interpolate pixels.

I don't know if the A300 has an optical zoom but you'd be much better off
with optical rather than digital zoom.

John

 

No.

With most cameras, you first have to separate the optical and digital
zoom factors. Optical zoom gives real resolution increase, digital zoom
does not. I think the A300 does not have any optical zoom, so this
isn't a factor.

Now, a digital zoom factor of 5 means an enlargement of 5 times in both
width and height, so an area that was originally 1/25 of the image is
enlarged to fill the whole image area. In this case, with 5.1X digital
zoom, the number of sensor pixels contributing to the output is

3.1 / (5.1*5.1) = 0.12 megapixels, or 120 kpixels

or about 400x300 pixels.

Thus, any final image size larger than 400x300 is likely to look
unsharp.

Dave