There's no questioning the resolving power of the Pentax D FA 100mm F2.8 Macro WR. At its peak it has no problem making the most of the high-resolution image sensor used by the Pentax K-1. It's also priced reasonably, built sturdily, sealed so you can use it all types of weather, and focuses close enough to capture images at life-size. But the amount of color fringing it captures is problematic, and the long focus throw and lack of a limiter switch can certainly slow focus acquisition. There's some room for improvement here, and we hope Pentax revisits this lens design to deliver performance similar to more modern competition like the recent Tamron 90mm Macro.
The word classic is overused, but I can't think of a better one to describe the Pentax SMC FA 31mm f/1.8 Limited. We live in a society where it's common to trade-in a perfectly good smartphone every two years, drive a car for three of four, and just look at technology in general as disposable rather than lasting. Pentax has kept the SMC FA 31mm f/1.8 Limited in produciton for 15 years, an eternity in the digital age, and many photographers have waited patiently for the company to deliver a full-frame digital body to use it as it was intended—as a wide-angle lens.
Tests at 16mp
Pentax SMC DA 21mm f/3.2 AL Limited
Pentax SMC FA 31mm f/1.8 AL Limited
Pentax SMC DA 35mm f/2.4 AL
Pentax SMC DA 40mm f/2.8 Limited
Pentax SMC FA 43mm f/1.9 Limited
Pentax SMC D-FA 50mm f/2.8 macro
Pentax SMC DA 70mm f/2.4 Limited
Pentax SMC DA* 300mm f/4 ED [IF] SDM
Pentax HD DA 16-85mm f/3.5-5.6 ED DC WR
The Pentax HD DA 70mm F2.4 Limited ($499.95 direct) is a compact, short telephoto compatible with APS-C SLRs from Pentax. It covers roughly the same field of view as a 105mm lens on a full-frame and captures images that are quite crisp. It's part of the company's Limited lens series, and as such boasts a sturdy all-metal construction, as well as a compact design. But it omits the weather sealing that you get with even entry-level Pentax cameras. Its aperture is also a little narrow, especially when compared with the Pentax SMC FA 77mm F1.8 Limited ($899.95), a full-frame lens that's built to the same standard, and is quite compact in its own right, but more expensive.
By the way, Nikon announced a 24-70 f/2.8 for $2400. A Pentax D FA* 24-70 f/2.4 would cost more than that, same for a 22-72 f/2.8. Adding half a stop is not free, nor can you keep unchanged the size of an already large lens.