OK, it's a nice a camcorder. Link, comment.
This does appear to be a nice 1080 camcorder so stock settings should get you 1080 but on a 27 inch iMac that's more than 1080 -> http://www.apple.com/imac/specs/
The 21.5 inch iMac is exactly 1080 so you should see exactly 1080 pixel for pixel there.
As noted by boya84, settings and lighting as well as any extra steps would be needed to be told to tell more.
Then again, could it be defective?