I own the DA 55-300mm, had the DA* 50-135mm and briefly tried out a Pentax pro's DA* 60-250mm.
For zoo shots the longer the focal length, the better so for a cheap option, the consumer grade DA 55-300mm will do fine. Adequately sharp but some colour fringing in high contrast scenes, but definitely much better than the Sigma or Tamron consumer grade tele lenses.
Depending on your distance to the subject, the DA* 50-135mm can be too short in terms of focal length and won't really throw the fencing for caged animals OOF enough, even at f/2.8. For small animals and birds, 135mm won't hack it, even the budget DA 50-200mm is better in this regard. Now the DA* 60-250mm is an altogether different animal compared to the el-cheapo DA 55-300mm. Superb from f/4 onwards and excellent in terms of optical performance, imo even more versatile than the DA* 50-135mm. Most definitely a special lens that is well worth the money, especially if you consider it can replicate the DA* 50-135mm, DA* 200mm and DA* 300mm in zoom range. To me it is the dream tele zoom.
Another factor to consider is that lenses with SDM have the edge in not spooking shy animals. The DA 55-300mm can and does hunt on occasion, and that screw drive sound has startled some animals in quiet settings from my experience.
Last edited by creampuff; 07-23-2009 at 12:02 AM.
Reason: spelling