I'm searching a more high resolution GeoTiff of http://www.naturalearthdata.com/downloads/10m-raster-data/10m-natural-earth-1/ since these are not sufficient if you need to zoom in...does anybody know a good source (free/paid) ? Thanks.

That website comes with a forum, have you bothered asking there for help as well?

No, but thx for the hint...

EDIT: You cannot register anymore and the last forum threads are very old, there...