Hi there! I have a Soligor 300mm f5.6 t-mount lens for sale. This is a pre-set variety and can be used with any camera with the appropriate t-ring. Has a rotating 1/4-20 mounting collar and an extendable dew shield/sun shade, along with caps for both ends. Housing shows a bit of wear in the paint and the front lens seems to have a tiny spot of mold (~1mm in diameter - didn't show up in any pictures that I took of the lens) on the inside, but this has not impacted the pictures I've taken with it. Could doubtless be removed by someone proficient in the cleaning of camera lenses.
I've taken some nice pics of the N.American nebula and Orion nebula with it. This lens will allow you to move from piggyback astrophotography to prime focus work gracefully. $60 shipped or trade towards an 80mm short tube refractor.