Thanks to all!
And special thanks for your hint, Mr Lamppost.
It was already scaled,
here is an unscaled version:
http://farm4.static.flickr.com/3110/3173016100_c7f7fc08cd_o.jpgScaling won´t be a problem for single objekts, I can make them the size I want.
But I had something with populations in mind, that could be a problem.
That strange noise inside the crystal (watershader) doesn´t disappear with higher quality, it just gets a little finer. reminds me of laser sparkling.
Until now I just made full renders with more than 0.35, little crops up to 1. Rendertimes are killing me.
Best regards,
Jan