I've found what seems like the ideal lens for me, the Sigma 300-800mm f/5.6. Now it costs $5000, so I'm not likely to buy it this decade. But it looks like it only comes with Sigma, Canon, and Nikon mounts. No Pentax. Well, if I buy it, I suppose it would be no big deal to add another 5-10% to get a camera to dangle from the back.
Pentax has a 250-600mm for around $7000, and although I'm not going to be getting that one this decade, either, it's still a little short for my tastes when it comes to birdies. Photography can be expensive.
