Originally posted by Rondec Let me say that it isn't surprising that Sigma didn't sell many Pentax lenses. The ones that made were problematic. Most were (are) low quality lenses that are prone to flare with their main sales quality being that they are cheap. The 35 Art and the 18-35 f1.8 were the "best" lenses that Sigma produced for the K mount and even those were problematic from an auto focus standpoint, with many copies producing sub-optimal results.
If Sigma released some of their better lenses for the K mount and made the effort needed to make sure that the Pentax focus protocols worked for them, they would probably do better,
Hmmm... I typically agree with a lot of your opinions, Vincent, but not here - not
entirely, at least.
I don't have many Sigma lenses across my combined kits, but I have a few...
Only my very-low-end film-era 28-80mm Aspherical f/3.5-5.6 (I own it in Minolta AF / Sony A-mount) could, IMHO, be described as "low quality" - by which I mean, it feels cheaply made, sloppy, with light-weight plastics and a plastic mount, no damping etc. It's clearly made to a low price. But optically, it's actually decent in its class (compared, for example, to the non-SMC Pentax-F 28-80 f/3.5-4.5).
My 18-300 in K-mount is clearly a consumer-level lens, but it's solidly made and well finished, nice to use, and turns in a pretty good optical performance for this type of lens... better than Pentax' own 18-270, which I previously owned.
My 17-50 f/2.8 HSM is a step up in quality, and whilst nowhere near the level of, say, DA* lens construction, it's
much better than typical kit lenses. Optically, it's very good, outperforming the DA*16-50 in certain respects. Flare performance
could be better in certain situations, yes, but I wouldn't say it's
prone to it... I've had very few issues.
The 30 f/1.4 Art is
beautifully built - I actually had to check whether the body was synthetic or metal (it feels like the latter, but is, apparently, the former), the focusing ring is a delight, and everything feels very tight and precise. Optically, it seems to divide folks - but I love it. And I've had no flare issues whatsoever.
I
will agree that AF is an issue, though. My 17-50, whilst generally pretty good, has missed enough AF attempts on the first cycle (not that many, but enough) that I typically focus twice to be absolutely certain it's precise (probably overkill, but it's become a habit by now
). My 30 Art hasn't shown any focus issues, but has a reputation for it. I use it with centre AF point generally, which is a somewhat preventative measure (though that's often how I shoot anyway), so perhaps that's why I've had no problems. The 18-300 seems accurate, but it's a much slower lens so perhaps I simply don't notice an issue if there is one...