# megapixels <---> zoom

Discussion in 'Digital Photography' started by Jim, Oct 17, 2003.

1. ### JimGuest

I'm just interested in knowing how to value zoomfactors / megapixels ;

For example, I'm reading about the specs for a new Panasonic Lumix
camera. It's a 4 megapixel camera with 12x optical zoom.
When taking a snap with maximum zoom, how many megapixels would I need
(without zoom) to reach the same resolution level? (on a cutout from
the higher megapixel cameras image)

I know it also depends on optics quality, CCD etc. But just roughly?

Thanks folks,
Jim

Jim, Oct 17, 2003

2. ### Timothy LangeGuest

Duh, 12 times, so 48 megapixels. This a trick question?

Tim.

Timothy Lange, Oct 17, 2003

3. ### marblesGuest

(Top-posting corrected.)

Duh, yourself, Einstein.

Maybe he was thinking it was geometric or exponential.

For example, if a 2x zoom resulted in a doubling of
the linear edge dimensions, that would mean 4x the
pixel count, right?

So a 12x zoom, with 12 times the linear dimensions,
would mean 144 times the original 4MP, or 576MP
would be required.

Your computations are based upon "2x" meaning
not twice the image linear dimension but twice the
diagonal measurement, right? This means the linear
dimensions increase by a factor of 2^-2 or 1.44,
right?

But I'm sure you knew that. Otherwise, you
wouldn't have been so condescending.

marbles, Oct 17, 2003
4. ### Ol' BabGuest

Double duh. It's 12 squared, or 576 Mp. Assuming this super camera's
fl-to-chip-width ratio is the same as the zoom at it's widest setting.
Ol' Bab

Ol' Bab, Oct 17, 2003
5. ### marblesGuest

Must be a Boilermaker.

marbles, Oct 17, 2003
6. ### Jerome BiggeGuest

I find a good "rule of thumb" is that you need about one
megapixel per "x" of digital zoom. Thus a two megapixel
would support 2x, a 3 megapixel 3x, and so forth. So you'd
need a 48 megapixel camera to equal your 4 megapixel
camera with its 12x zoom. This is assuming that optical
quality of the lens was up to the job... This was "doable"
with film before digital came on the scene. Shoot a scene
with Kodachrome 25 or other ultra fine grain film, and enlarge
the picture just as far as grain and optical quality would allow.
Also was an excellent way to determine actual lens quality.
Today you can do the same with a good slide scanner.

The sharpest 35mm camera lenses were usually the
50mm focal lengths working at about F8. You can get
a real debate going whether or not the Nikkor 50 F1.8
was sharper than the Canon 50mm F1.8, etc. My own
experience indicates that there was enough sample
to sample variation that "luck" was the determining
factor... Spent about 14 years all together in the
photo industry.

Jerome Bigge
Member, Muskegon Astronomical Society
Author of the "Warlady" & "Wartime" series.

Jerome Bigge, Oct 18, 2003
7. ### NimousGuest

What u tells about the 50mm lenses is what i'vr learned aslo.

About megapixels/zoom.......wouldn't u need more mepapixel pr "x" for each
"x" u go?

Nimous, Oct 18, 2003
8. ### Dave MartindaleGuest

He was wrong, but so are you!
So far so good.
Diagonal measurement is a linear measurement, just like height and
width. If you double the diagonal, you double the width and height at
the same time - you do not multiply by sqrt(2). By the way, 1.44 isn't
sqrt(2) either.

Dave

Dave Martindale, Oct 19, 2003