Why does the 21mp 5D2 put out a 2mb Jpeg?

A bit more info:

I shoot raw most of the time.
When I convert this to full sized jpeg in Lightroom I get a 10mb file.

When I shoot in Jpeg I end up with 2mb files even though it's set to full size.

No big deal but can't understand the discrepancy? On looking the pixel dimensions are the same.

The size of JPEGs vary on the subject matter being photographed and the compressions options that the JPEG encoding utilise.

From memory I thought most JPEGS straight from the 5D2 where around the 3-5 Mb size, but like I say it varies greatly on the complexity of the subject matter.

Try taking a picture of a single colour wall with no detail on it and then try taking a picture of a forest/woodland scene with lots of branch/leaf detail.

Cool, thanks for explaining that.

On another note, I remember seeing there was a colour adjustment page on the web.

Essentially if you have a grey background but it looks blue on camera it would tell you which of the RGB colours to adjust?

The on-board noise reduction that goes into producing the JPEG may also contribute to the file size as, typically, less noise means smaller file size (more efficient compression).

WRT your "gray background" question - you are referring to White Balance. That is, you need to tell the camera what kind of light you are shooting in to make sure it renders neutrals (grays) neutrally. If a neutral looks too blue, you have your WB set incorrectly - it needs to be more orange/amber/yellow. You don't need to adjust individual colors, just set the white balance properly by choosing the closest preset WB on the camera (Daylight, Tungsten, Shade, Fluorescent, etc.) or use a custom white balance by taking a picture of something you know is neutral and then setting that image as your Custom WB - read the manual to see how you do this. It is very straightforward and takes a few seconds once you get the hang of it.

Kirk