Well, hello again, after being "away" for quite a while! Thought I'd bring you all up to date on what I decided and did regarding my concerns back in 2017 (!).

On the basis of cost, I in fact tried to buy the Sigma 50-500 mentioned earlier. But it turned out that Sigma was stopping production of that model in the Pentax mount at that very moment, and I was unable to get one. So I had to turn to the Pentax 150-450. I waited a while and managed to get it at a reasonable sale price, so that was good. I've been VERY happy with this lens, but although I had read all the specs and knew what I was getting, it is VERY heavy. I've gotten used to it, though, and to lighten my load in the field I've switched from a pretty heavy tripod to a nice sturdy monopod. This combo works pretty well.

So now I have a NEW question: I sometimes wish I had a little more "reach" than the 150-450 lens gives me, so have been wondering if Pentax's 1.4 teleconverter would work well with the 150-450 zoom (making it roughly a 210-630 zoom) or would be just a silly waste of money. I've read user reviews that say the converter works well with Pentax 300 mm and 55-300 mm lenses, but am wondering how it would perform on the upper end of the 150-450 zoom. Anybody have thoughts on this?

Thanks,
Jim

Hello, Everyone:

Thanks to you all for your responses to my question!

The overall message I'm hearing so far is that my K-3 should be fine for what I want to do, but that I may indeed want to consider a new lens. I think I'll experiment a bit more with what I have to see if I can improve on my results before taking the new lens plunge. (Yes, the Pentax 150-450 looks good, but so does the Sigma 50-500, which has a longer reach and is less expensive. I read positive responses from some of you on both of these; the response about throwing one of the Sigmas in the dumpster was a bit concerning, however...)

Thanks again. As requested, I'll let you know where I end up going with this.

Jim

I'm Jim, a new Forum participant interested in wildlife photography. I've been a Pentax user for a very long time, and mostly satisfied with my results. For wildlife shooting, I am using a Pentax K-3 with an old Sigma 170-500mm zoom, and am not entirely satisfied with my results in this area. Two problems I seem to be facing are: 1) lack of sharpness when shooting at greater distances and the high end of the zoom range (usually with a tripod), and 2) slow focusing response when trying to shoot moving subjects. Actually, I guess there is a third concern as well: In addition to being slow, the focusing mechanism on this old Sigma is very noisy, to the extent that it has sometimes scared birds away before achieving focus. So I've been wondering if I need to replace the old Sigma zoom with a newer version (options seem to be the Pentax 150-450 zoom and the newest version Sigma 50-500). Can I expect to experience satisfactory focusing speeds and sharp images with one of these lenses on my K-3 or should I be considering jumping to another brand, say Canon or Nikon, to get the results I'm looking for?