Originally posted by nanok just one more thing to add: all pentax cameras i've used (k100d, k10d, k20d, k-5 now) will allow you to zoom in way beyond the actual size of the picture (1/1), which can be very confusing (there should be a marker at the 1/1 position, imho). what i do is find the "maximum reasonable" zoom level, so i know where to check for sharpness (what to expect).
The rear screen on the K-7 and K-5 displays 921,000 dots. This is actually represented by an array of one R, G and B dot per pixel on a 4:3 screen, so:
640x480 pixels x 3 dots = 921,600 (hence the 921K dot LCD in the specifications)
Keeping this in mind, you can figure out that x8 magnification is closest to 1:1 (x7.3 would be ideal on K-7, and x7.7 on K-5, but it jumps from x6.7 to x8). Anything beyond x8 can be misleading for judging sharpness.
On a K-r, the 1:1 magnification is exactly x6.7. But on a K-x, you need to zoom into x11 to get 1:1 because of the much lower resolution screen.