As far as I know there aren't any problem areas with it. Its a very solid all round performer.
Its biggest problem is the existence of the DA* 300mm f/4 which has developed an equally strong reputation as an all round excellent lens. The issue for the FA* is that the DA* is weather-sealed, available new with full warranty, SDM and has a much shorter minimum focus distance. The downsides are its a bit heavier and bigger than the FA*
I would say its worth getting -
A) if you can't afford the DA* (and are unlikely to be able to save the money any time soon) and the FA* is a decent price
B) if you're a bit of a lens collector because the lens is not so common (in the UK anyway)
Wonderful lens -- sharp from wide open. Acceptable bokeh. Very hand-holdable. Too slow for low light; Great with lots of light. Not much selection in AF teleconverters if that is a consideration. If you're considering this for APS-C (i.e. Pentax digital only), my recommendation would be to do your homework on the DA*300/4 prior to making a decision. Dave
on the weekend i have the opportunity to check n mount the lens on my K10d.
I really want to buy this, but is it worth it (i know i depends on the price, which i don't know yet)?
I mean it is a bit slow, i think. Is there anything i have to have a lock at especially with this lens?
Deimo
That is one heck of a lens. Go for it. Anything under the price of the DA* 300/4 would be good, if it is in good condition. The difference in speed between f/4 and f/4.5 is almost meaningless.
I shouldn't say this as I would love to get one again (regret selling mine more than any other lens I have sold) but the f*300 is the best of the 300mm lenses IMHO..
I'd say if the price of it is reasonably lower than DA* then go for it. I bought my just a few weeks ago for 549GBP which is almost half of new DA* and still considerably lower than used DA*, here in UK that is. The lens is excellent IMO. The only think I wish it had is the tripod collar. Not that it's heavy lens (actually is really small and compact for 300) but if I'm trying to keep the ISO down (I use K10D) then the camera shake is an issue and the setup on monopod feels bit weird.
Other than that I love this lens annd the IQ is great.
I don't have the FA* but I have the F*300/4.5, which is my best 300mm lens: sharp, exempt from chromatic aberrations, well built, compact and relatively lightweight for the focal length. Its only drawback is a bokeh that can be a bit distractive on some shots, but really nothing terrible. To me, its main advantage over the newer DA*300/4 is the aperture ring, making it easily usable on other cameras. I can use the F*300 on my old K mount Pentax film cameras, on my Canon DSLRs, and even on my Micro 4/3rds Olympus E-P1. The newer DA series are only usable on recent Pentax cameras, due to their lack of an aperture ring on the lens.
I did not buy it.
It was a very used one, it made funny noises when shuttering.
and the hood was hard to fix, there were also a few visible dots inside.
The price was appr. 850USD, so i decided to wait for the next one.