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

Discussion in 'Digital Photography' started by lbbss, Jun 10, 2004.

1. ### lbbssGuest

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?

lbbss, Jun 10, 2004

2. ### John BriggsGuest

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

John Briggs, Jun 10, 2004

3. ### Dave MartindaleGuest

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

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

Dave

Dave Martindale, Jun 11, 2004