Are you looking for an HD or SMC version or does it matter to you
HD vs. SMC Pentax Limited Primes
Introduction
At Photokina 2012, Pentax announced a brand new lens coating which they named the "HD Coating". This coating is slowly starting to replace the conventional "Super Multi Coating" (SMC) on high-end Pentax glass. According to Pentax, the new HD coating greatly reduces reflectance without making any sacrifices in terms of durability. This kind of coating isn't new to the industry, however: Pentax digital medium format lenses have been treated with a slightly less durable variant called Aero Bright coating ever since their debut, and other manufacturers have been using "nano" coatings on their premium lenses for several years.
The modern SMC coating that DA lenses have been using for about a decade now isn't the same as the SMC coating that Pentax originally launched in the 1970's. In fact, most DA lenses have been said to have a "ghostless" coating, so while we don't expect the difference between SMC and HD coating to be be a game-changer, it should certainly still be easy to observe. . . .
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HD vs. SMC Pentax Limited Primes Review - Introduction | PentaxForums.com Reviews