Hi Ronny,
I use a Voigtländer 90mm f/3.5 SL II APO-LANTHAR lens, usually stopped down to f/8 or f/9. While this lens is out of production for Nikon and Pentax mounts, it is still available for Canon. Scroll to the bottom of this page for more information on the optic. Please be aware that this lens is manual focus only, and is adjusted for each specimen by confirming focus using the camera’s live-view function.
For lighting, I use a floor lamp with a single PAR 20 Solux bulb and two collapsible white/silver reflectors to provide a little bit of shadow fill. This bulb has a consistent color temperature, full spectrum reproduction, and very good illumination. With this lighting, images are always made using a tripod. Fossils are placed on a black towel to minimize backscatter and an X-Rite ColorChecker Passport is used to indicate scale and provide a neutral color balance point in the image.