Peter asked: "I was thinking about A 70-210/4... Is it really that good?"
Yes, Peter, it is that good. Pentax made three or four manual-focus zooms whose results are, in every respect, indistinguishable from a great prime. The 70-210/4 is one of them. The others that come to mind are the 35-105/3.5 PKA and 75-150/4 (M? K?). Another PDMLer writes that the Tokina ATX 100-300/4 is available now at KEH for less than $200. If you don't mind manual focus--or, indeed, if you prefer it--grab it. This is one of those third-party lenses that you'll find every week on eBay--in the wrong mount. If you don't like it, you won't lose much in the resale. Paul Franklin Stregevsky
