So I have (2) x2 very sharp MD/MC Teleconverters and would like a 70-210 or prime that is larger than 170 or so. I currently have won an auction for a Minolta MD 70-210 f/4 in mint condition for $55 total, but then learned that with a 2x teleconverter it will only be able to do f8 at its fastest. So, are there any good long primes for MD/MC that are faster than f4? Even if its a 150mm it may be fine. Just want to know if there might be any good vivitars, sigmas, or others out there that are f3.5 or f2.8 or something. I don't like to do this and never have, but I do have the option to not pay for the 70-210 and save my money for another better MD/MC lens. I will use it primarily for moon shots when using the teleconverter, but would like to be able to use the teleconverter for other thngs. Thanks!