pentax 300mm da
Pentax DA 50-200mm f/4-5.6 or Pentax FAJ 75-300mm f/4-5.6?
The quality not price.
Remember the long focal length, the harder to take a clear, unless you use a tripod. If the price is not a problem, go with one goal more quickly, something in the range of F/2.8-3.5. Moreover, depending on what is combined with a 18-70? 18-55? Choose whether you get a wide range of viewpoints. Furthermore, it is limited to a few lenses, Pentax look both Sigma Tamron and negative consequences, while its camera products.
Pentax K-7 with DA*300