PENTAX 300mm F4ED IF SDM LENS

The DA* 300mm uses Pentax's current-generation KAF2 lens mount, which updates the basic K mount with communication contacts for basic lens function control, as well as a pair of contacts supporting the lens's SDM internal AF motor.

Back compatibility with older DSLRs that use the first-generation KAF mount (the *ist cameras, for instance) as well as newer K digitals not running the latest firmware is ensured through the inclusion of a screw drive connection on the mount as well.

Feeling intrepid, we actually taped up the lens's KAF2-specific AF drive contacts to see if it would be possible to improvise an auto focus solution in the unlikely event that the internal focusing motor should fail, but while we succeeded in disengaging the SDM drive, we could never make the screw drive engage. Clearly there's some other communication voodoo at work in the KAF2 mount that lets the body know it's dealing with an SDM lens. There may yet be a simple field solution (short of reverting the firmware on your K10, that is) to accessing this backup drive function, however, which would be a boon for working photographers looking for AF system redundancy.

Design and Build Quality

Pentax has supported lenses similar in basic construction to the latest 300mm for several decades now, though the DA* version adds some key upgrades to this basic formula. As noted, the lens – like all of Pentax's DA* high-end optics – uses an internal supersonic focusing motor (a technology termed "SDM" by the manufacturer), as well as a traditional screw drive connection for focusing support on older Pentax digital bodies. Likewise, the new lens is sealed against water and dust, with a gasket at the lens mount providing an impervious connection to Pentax's weather-sealed DSLR bodies.