Originally posted by Trickortreat Dunno, sigma 30 1.4 is optically better than 1st party options of comparable fl. Af sucks for that lens tho...
And i found both sigma 17 50 2.8 and tamron 17-50 2.8 better than 1st party options for all dslr manufacturers. Only their build quality somewhat lacks but they are ok for most of the tasks...
The comparison on this website showed the 31 ltd was better at a given ƒ-stop, the 30 1.4 was better (creamier bokeh) at 1.4 than the 31 was at 1.8, but that was it. Not only was that the testers opinion but he posted comparison photos so we could make up your own minds. To me the difference were clear, and the 30 1.4 was really only better in price. (unless you really shoot in manner where 30 1.4 is a thing.)
With the Tamron 17-50 there are numerous reports of de-centering, which mine suffers form as well. You can't use it for landscapes even at ƒ8. With older lenses like the 17-50, you don't get water residence and the build quality isn't as good. So in our experience better out of the box, but 5 years later, not better. I simply refuse to compare WR lenses with no WR lenses. Those water seals make the lenses smooth in away non-WR lenses doesn't seem to match.
Personally, after starting off on a 3rd party lens shopping spree to keep costs down, almost everything I used to carry has been replaced by Pentax glass.
The 3rd party lenses still in use are the Tamron 90, which my wife loves, but I've picked up a DFA 100 macro for my own use, The Sigma 8-16, Pentax doesn't make a similar lens, and my Sigma 70 macro which has been used infrequently since I got the DFA 100 macro, and my Tamron 300 2.8. Look at the reviews you can see all those lenses get stellar reviews. But they are all in focal lengths Pentax doesn't make, which is how I've always seen 3rd party lenses. They have to fill holes in the Pentax line-up.
You could do a whole 3rd party lens thing and not buy any Pentax glass, but this point of my 22 lenses, only 4 aren't Pentax and those 3rd party lenses get used a fraction of what my Pentax lenses do.