but it is slow.
But for people to ask what lens? without giving a description of what they are shoot and what they spend, most people just through out lenses that they have or would like to have. The 135mm maybe great but but not very effective if you need a 200 or 300mm. The 70-200 f2.8 IS is great but not if you only have $300 to spend.
Pat, if you want real answers you need to give real uses and budget.
As others have stated, the rule of thumb, faster-constaint adapters (f2.8 or f4) are best, IS is a must for telephoto handheld shooting. Combine the two and you are looking at expensive glass but well worth it.