Originally posted by Dauntless 
WPRESTO, you were right about the 55-300 lens. I'm not getting the results I expected. Actually, I think the picture quality is not much better than my Panasonic FZ-200. What lens are you using for bird photography?
I used a Bigma (Sigma 50~500) for many years (purchased one soon after it was introduced). When the Tamron 150~600 came out, I hoped against hope it would be made available in Pentax mount, but as it was not, I purchased a Nikon body so I could use that lens. Up to about 500mm it's better than the Bigma. At 600mm it's about the same as the Bigma at it's maximum, but about 1/3 longer (the Bigma tops out about 450mm, not 500mm). I've gotten some good images with the Tamron, but I don't especially like the "feel" of the Nikon body (BTW: I also have a Nikon 18~140mm to go with it, plus an old 50mm f1.8). More recently I got a Pentax 150~450mm that I haven't had much opportunity to use, however tests indicate it's as good or better than the Tamron through their overlapping range. I also tested the 150~450 with the HD 1.4X TC and found the results very good. The two seem to be very compatible. At maximum (~630mm) the 150~450 + 1.4X seem to be a touch better than the Tamron. I also have a very old 400mm f4 Tamron Adaptall with Pentax mount, and use it with the old 1.4XL and 2XL Pentax TCs. That old Tamron is excellent, and seems to pair well with the 2XL providing 800mm f8, but focusing is extremely difficult and vibration is a major problem. BTW: both the Bigma and the 400mm Tamron were in my possession long enough to require professional CLA (major spots on interior lens surfaces) and both came out beautifully. The Bigma has gone on to another Pentaxian. I cannot quite part with the 400, but it is not an easy lens to use. Set up with the 2XL it requires both my heaviest tripod and a secondary support below the camera body if I want to realize the potential IQ. It is strictly a location rig (= I have determined where there is a bird, where to set up a camera and perhaps flash, and go with the sole purpose of imaging that bird).
That should be more answer than you wanted to read.
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