i would like a 500mm lens, but there are two problems, 1, there is no way on this earth that i could afford a prime? lens in that size, 2, i might not put it to enough use?, all i am thinking is getting a cheap 500mm f8 mirror lens, would it be ok for a noob and complete beginner like me, or would i just be wasting my bit of cash. unless anybody has an old one lying about i could borrow 
