Summary: 12x zoom is 1:1, but the usefulness of 1:1 on that screen is questionable.
So here's what I did. I took a photo. In this case, it was just blackness, but that's irrelevant. I opened it in the GIMP and pasted it full of a 1-pixel horizontal line pattern. Then I cut out a rectangle, zoomed way in, and pixel-penciled the word 'test.' (see below).
Unfortunately, the camera would not display the resulting image.
Then I found
jhead, which allowed me to transfer the full JPEG header from one file to another. Problem solved.
Now, at 12x zoom on a K10D, the horizontal lines are perfect 1:1, and I count exactly six lines beside the white box, just as it should be. The problem is that the 'test' text is not perfectly sharp. Viewing a pixel-edited image at that zoom level reminds me of looking closely at the TV. Technically, a standard-def TV can display around 480 lines of resolution, but that doesn't mean those lines will ever be sharp.
So 12x it is, but does it really matter?
Btw, I included step-by-step instructions so that other people can do the test with other camera models. If you need more help, pm me.
Last edited by joefru; 05-21-2008 at 06:00 PM.
Reason: to quell the flames