The telescope acts as the camera's lens - there is no other lens present in this basic configuration.
Large telescopes are all reflectors, using a primary mirror at the back rather than a lens at the front (which would be a refractor). This is because a mirror can be supported all over its back, so its weight does not distort it.
Some have a central hole in the mirror and the secondary mirror reflects the converging cone back through this hole - the Cassegrain design. One advantage of this is that the secondary mirror can be a silvered central spot on a glass plate, requiring no metal vanes to support it. There are several variants of this design (eg, Maksutov, Schmidt).
Dobsonian telescopes are Newtonian - they differ in the way they are mounted.