I would be very interested in hearing other owner experiences and I also wonder if Adam played with the Fine AF adjustments on the K-3s. Clearly CDAF is a no-stress option (I love the K-01), and I may never totally trust PDAF on this lens, but I think it may work out after all. So I am now inclined to keep the lens, get a dock, and finish adjusting settings even better. I am verifying all this by shooting Live View and then PDAF for every shot. It is still missing once in a while, but overall not too bad. Even shooting at 1.8, using PDAF, I am getting pretty decent hit rates. I was able to take a lot of test shots, and readjusted the Fine AF settings on my K-5 after a lot of testing, and the keeper rate has improved dramatically. Clearly, this lens is VERY sensitive to FINE AF adjustment on the K-5. OK, I have had several more days to experiment with my new Sigma 18-35 on my Pentax K-5. And the infocus shots seem totally random.< And I adjusted the fine AF in my Pentax K-5. I MEAN MOST WERE OUT OF FOCUS, NOT A SMALL PERCENTAGE, LIKE 85% BAD. SOME PICS WERE IN FOCUS, OFTEN THE CLOSER FOCUS SHOTS AND MACRO, BUT GET ANYWHERE NEAR INFINITY AND THE FOCUS DOES NOT WORK RELIABLY AT ALL. >HOWVEVER, USING PDAF ON MY PENTAX K-5, I HAD THE SAME ISSUES AS ADAM. Selecting the AF point myself seems to help too, but I haven't really tested auto selection much I don't really trust it to give me what I want and at large apertures, that will result in horribly misfocused images. With the FA, I can hear the screw drive move a bit even after the initial focus confirmation. A trick I use with both is to hit the AF button multiple times at low f. I have found focus to miss a fair amount, but I don't think it's a lot more often than my FA50 or F50 f/1.7 miss. I think if you were experiencing anything like the review's encounters, you'd know it immediately. The review suggests that nothing is ever in focus at any f stop (seems hard at f/8 and 18mm, considering DoF is basically infinite). Once I've had more time to experiment, I'll comment more.What camera and firmware are you using? That said, it's no where near as bad as the in depth review seems to suggest. I've only had a short time to mess around with it, but I feel that the af is pretty inconsistent. I just picked up my example if the 18-35 yesterday. Corrections with the Sigma dock may help, but I kind of doubt it. So this is a great lens on the K-01, or using the clumsy live view focus on a Pentax DSLR (good luck), but forget using it with PDAF.until maybe a firmware update? I hope Sigma goes back to work this problem, which is clearly in the lens software (not optics) and has been reported with users of some other brands as well. And the infocus shots seem totally random. HOWVEVER, USING PDAF ON MY PENTAX K-5, I HAD THE SAME ISSUES AS ADAM. I love the K-01 even more after this test, as without it, Pentax fans could not really use this lens. Bravo to the K-01 which will probably sell like crazy now. I had not one out of focus pics out of hundreds taken today, under all kinds of light and conditions. The CDAF is pretty fast, very quiet AND EXTREMELY ACCURATE. On the Pentax K-01 v1.05, this lens is fantastic. The Sigma AF is so quiet it can hardly be heard, if at all, when the K-01 is taking video. The Sigma underexposes at 35 1.8 for some reason with some vignetting. The Sigma 18-35 and Pentax 16-50 were pretty much equal in the centers at 18 and 35, but the Sigma wins out at the edges especially from 2.8 to 4.0. The Pentax matched the Sigma at all f stops except 2.8, where the Sigma has just slightly better contrast. My Pentax 20 2.8 FA is a great small lens, and is full frame. At 35, the Sigma was just a little sharper than my Pentax 20-40 overall. At 20, the Pentax 20-40 is very close but the Sigma beats it just slightly in the extreme corners. Sigma 18-35 is optically superb across the frame. I tested at 2.8, 4, 5.6, 8 where possible. I have good, pretty centered copies of all these lenses. The Sigma 8-16mm f/4.5-5.6 has flare issues and has difficulty acquiring focus in back-lit situations. Tested it carefully with K-01 versus Pentax 20-40 Ltd, Pentax 20/2.8 FA and Pentax 16-50 DA*. The sigma 100-300mm f/4 APO EX flares easily and it has no focus limiter, the Sigma 180mm f/3.5 APO EX has flare issues, and isn't critically sharp at any aperture with focus distances greater than 15m. Window._PLUGIN_STATE_ = JSON.I just received a brand new Sigma 18-35.
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