Originally posted by ben_leg But looking at the different thread around here, it seem that the DA* have a reliability issue.
The sad truth is, they do.
When the SDM issues started there was a lot of hysteria and I was one of the few stating that there was too little evidence to justify a
petition, etc. Since then the SDM failure reports haven't stopped. Surprisingly many have their lens fail not once, but twice or even three times.
Lenses can fail, yes, but in particular these multiple failures with single individuals and the frequency with which I read about SDM failures tells me that there is a fundamental problem and that one does not have to be particularly unlucky to experience an SDM failure.
The primes seem to be more robust but in particular the 50-135 and the 16-50 seem to be affected a lot. It would have been more than appropriate for Pentax to increase the measly one year warranty to at least three years for a so-called "*" lens. In comparison, in some countries, Sigma lenses have six years warranty. Maybe it has to do with the fact that HSM failures seem to be very rare? Can you find a analogue HSM thread where users are happy like children at Christmas just because someone found a way to
repair a particular SDM failure?
I agree, optically the 50-135 is a gem, but if I were you, I wouldn't buy it without an additional warranty.
BTW, the AF of the 50-135 is slow. Period. Let's call a spade a spade. Screw-drive lenses experienced a boost through the stronger K-7/K-5 AF motors but SDM lenses will always have the same (typically slow) speed. In some cases, this is not a problem, e.g., the DA *55 is meant to be a portrait lens and hence precision is more important than speed, but you won't be able to capture fast action with the 50-135 to the same degree as with a quicker screw-driven or HSM lens.