I made a post a day or two ago, but it ended up in software. Here it is again:
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).
Instructions:
https://tamarintech.com/article/ciclop_scanner_focus_fix
I made a video:
https://www.youtube.com/watch?v=fJYqHhkq42M