The C270 has a fixed (manual) focus mechanism. The focus is just beyond the scanning platform. If you are consistently seeing out of focus images in your previews you might consider tweaking the manual focus (BQ Labs suggests this in their Google Groups).
- Remove the face plate, which you should’ve already done during the assembly
- Unscrew the three small screws. The second face plate should just fall out
- Locate the lense and turn the manual focus - it doesn’t move very far and has a stop. Tweak it a little to see if you can clean up your focus. You set the camera in the holder to check as you adjust.
I made a video: