Lengthening F.L.

Just wondering. I'm thinking of building my own scope will a
large 18" parabolic mirror. However, the focal legnth is only 6". Is it possible to stretch that out with a lense of some kind. I don't want to make this a Cass, more of a newtonian. Or would it be more feasable to try a hershelian design?
-Adam

You must have a typo in here somewhere, it's a mathematical impossibility for a mirror to have a positive focal length less than its radius. Did you mean 60"?