Hi,
Thanks for the tips to everyone.
I did not know about the adjustment of lens lens, thanks.
And that there is a club for 300mm. Impressive :-)
I find it too hard to write in words what I want to use an modern AF 300-500 lens for.
Pictures tell so much more, so please look at some of my nature and wild life images here.
https://picasaweb.google.com/117274245937836909186/Natur
I guess it is obvious which ones are taken with a long focal length. The Exif does not tell here.
I have been thinking about the weight issue. Normally I carry the 300mm mounted on a one-pole "tripod" (a one-pod?) for horizontal wild life shots, but the occasional buzzard, hawk or falcon of which there are plenty where I live, are often close to overhead so the pod gets in the way. Then it is hand held. This more or less rules out a 2kg+ lens for me (I think). Recently I purchased a good light weight tripod. I use this too especially for nature long exposure images.
I used to do a lot of astro photography.
I have used the 300mm but on astro ccd cameras with more flexibility regarding focus travel. I have never used the 300mm for astro on the Pentax DSLRs. It does not focus at infinity.
Stars are good for finding out if the camera kan focus sharply. If you know what a sharp star looks like; I want the lens to focus sharply at infinity for when I get back to astro imaging again, but also for nature imaing.
Macro is btw irrelevant for the lens.
I really don't like a bulky "unsharp" lens which is my impression in the review of the Sigma 150-500. There must be other alternatives.
A compromise could be the 1.7x AF adapter given its ability to "focus" an MF lens like my 300mm f/4. I wonder about IQ. The price is rather high, but if I end up with a combination which is sharp, can focus at infinity, has AF and a little longer focal length plus no need to stop down more than one stop then it might be just right.
I would find it amazing if the are only two alternatives; keep what I got or buy the modern 300mm f/4.
kind regards
Morten