Pentax DA 35mm F2.4 vs 40mm XS vs 40mm Limited
Autofocus Performance
It’s no exaggeration to say that autofocus performance has been the biggest technical bugbear for Pentax in the digital age. While Pentax dSLRs offer some of the best image quality money can buy, they have been routinely outclassed in terms of autofocus accuracy and speed by rivals from all across the manufacturer spectrum. While this trend has been on the mend in the last couple years, thanks to improved AF modules in the K-x, K-r, K-5, and K-01, there have still been embarrassing snags like the much-discussed tungsten focusing issues that have plagued some K-r and K-5 units.
We tested these three lenses on our K-5, which has thankfully been largely free of the abovementioned issues. Despite their traditional screw-driven autofocus mechanisms, each of the three lenses focused quickly and decisively on our camera. There was a bare minimum of focus re-adjustment once the camera had locked onto its target; we didn’t experience any “focus dancing” that some have complained of in the past.
This behavior usually held true in both the usual phase-detect AF mode and in live view-enabled contrast-detect shooting, though the contrast-detect mode would occasionally rack quickly through the entire focusing range before achieving lock. This snappy focusing behavior is probably down to a combination of factors, including the K-5’s strong motor, the lenses’ short focus throw, and their lightweight construction. On the noise front, the DA 35mm f/2.4 and DA 40mm f/2.8 Limited were louder than the DA 40mm f/2.8 XS when focusing, but all three are comfortably quiet compared to some other Pentax screw-drive lenses.
It’s worth noting that our DA 35mm f/2.4 review copy required -10 focus adjustment to correct persistent backfocus on our camera. Once the focus adjustment was dialed in, the lens performed quite well, as you’ll see in the tests to follow. Both DA 40mm lenses were dead on from the first shot, and required no adjustment whatsoever. As usual, we’ll chalk this up to sample variation and less than perfect quality control. And as ever, your mileage may vary—front- and backfocus issues seem to be very much about the way a given camera and lens interact with each other, rather than simply one or the other being objectively out of alignment.
The DA 35mm f/2.4 and DA 40mm f/2.8 XS have no focusing scale, which can be quite annoying for those who like to employ zone focusing, e.g. for street shooting. In addition to possessing a focusing scale, the DA 40mm f/2.8 Limited also gets points for including Pentax’s quick shift manual focusing option, which allows you to override the AF at any time. But we should keep in mind that the other two are budget lenses, and some compromises will inevitably be made in the interest of keeping prices down. Each user should choose the lens that best fits their intended purposes.
