Tough choices?????
If you are patient and really wanted a deal you could set up an alert with MPB by following this link:
Last time it came up on their site they sold it for somewhere between $200-250. I almost bought it just because it was such a good deal, but let someone else have it. One day I do want to try it out. It seems particularly good for a lighter hiking setup, and the faster AF does seem interesting to try.
It will probably take a month or more before you get a search alert on that lens, but if you're willing to wait...
Long thread and I'm late to the party but I thought I'd share my experience with Pentax and the Tamron 70-200.
You have a few options when it comes to fast 70-200mm range full frame lenses in a Pentax mount. I came to Pentax from Sony/Minolta and I had one of the legendary Minolta "beer can" lenses that can be found relatively cheap ( 70-210 f4 ). I LOVED my beer can. Coming over to Pentax, I could not find an obvious equivalent (a sharp full frame budget telephoto lens). The lower end off-brand 70-300mm lenses available for Pentax didn't have the build or image quality I wanted (based on reviews). Ultimately I found myself looking at the older but higher-end lenses made by Sigma, Tokina, and Tamron.
The Sigma was tempting because I have other Sigma glass. The build of older Sigma EX lenses is a love or hate situation. I personally like older Sigma EX lenses. One thing worth mentioning is the HSM variant of the Sigma 70-200 needs a firmware upgrade to work with the K1 or KP. That firmware upgrade is near impossible to have done now. So, if you find the HSM version make sure the firmware has already been updated or don't expect to have working autofocus on newer Pentax bodies. This may be a controversial statement, but I would personally prefer the screw-drive Sigma for this reason. What if the latest firmware (and probably the last firmware) for the HSM Sigma doesn't work on the Pentax K1-II ?
The Tokina 80-200 f2.8 is the lesser known option that can be found a bit cheaper than the others. Supposedly it's a great lens and built like a tank, but it's hard to find without fungus/haze.
The Tamron 70-200mm is prone to heavy internal dust. My copy was full of it upon arrival so I can confirm that. I have removed the front two elements to clean the glass twice now. Daunting at first but I'm a pro at it now. There are a few video guides online that show how to do it. The dust has never affected my photos.
Based on the above, I narrowed my search down to Sigma and Tamron. Ultimately I based my decision on what was available at the time (combination of price and condition).
A note on the Tamron auto-focus speed. Yes, it is a screw drive lens. The focus speed depends ( in part ) on the body you are using it on. The K3 had a much improved screw drive motor. I have a K5-II and a K3-II and the focusing speed and accuracy is vastly improved on the K3 when shooting with the Tamron. I'm not qualified to say the autofocus is "fast" as I don't tend to shoot motorsports or anything that moves faster than my kids playing soccer. For what I do, I've never thought "I wish this focused faster".
All that said, these are old, heavy, full-frame lenses. I really, really enjoy my Tamron 70-200mm f2.8 and I have absolutely no regrets buying it. That said, if you have zero aspiration to go full frame, and you'd like something small, lighter, possibly with warranty, and you can give up some speed, then the new PLM 55-300 seems like it would be a great choice.
Let us know what you wind up with!
It's a pity that Tamron or Sigma didn't do a 100-400mm in the K mount. that would be perfect.
When people say "wildlife" they usually mean birds and bird photography with a max focal length of 300mm is difficult and anything less than fast and accurate AF really ain't going to help.
Although I am a (poor) Nikon shooter, I have extensive experience with the 300mm handicap. I've been told that the Nikon and Pentax optics on the 300mm f4 are similar. I have a 500 something dollar 70-300mm and the 300mm f4 AFS (silent wave motor). While stopped down to f8 the zoom is a pretty sharp lens especially for stuff not far away. But optically , they are not in the same league and I can't speak for Pentax but the Nikon prime, is far faster. It's almost jittery it's so fast. Really think about it, the AF should be way bette across the board it's letting in so much more light. That said I was able to catch hawks in flight with the zoom.
The 300 prime also takes. TC. I use the 1.7. It does reduce IQ and AF accuracy and speed in lower light, but it buys you 500mm at f6.7. I see no advantage to stopping it down, unlike the zoom, which I get CA and just not as sharp wide open as it is 1 stop down.
The zoom is far lighter than the prime, fits into a camera bag, is cheaper and it's still a competent lens. I would guess the Pentax version would be similar and water-resistant. If I were the OP that would probably be the route I would go.
For Pentax we have the 150-450mm lens, but I'd like to get the 150-600mm from Tamron and Sigma
