I also made a comparison of the laserlines I could get with the lasers I used:
The linewidth of my focusable lasers is about 0.2mm, the lasers from dealextreme gave different results (but all of them are good, the thinner one is ca 0.12mm!) and my "old horrible" green laserpointer has a linewidth of ca. 0.9mm.
So throw away your red lasers and grab' a green one, no matter if focusable or not...
Thanks again for Mattia and Walter for helping me here.