Originally posted by NigelS There are threads for example on the DA 18-135 trying to find a solution repair for exactly the same issue as we are having with the FA 28-105 !
Actually, as I believe most who have been regular in PF for a length of time can verify, the DA 18-135mm lens has been exceptionally dependable with fewer reports of defects than most. Even though having the same AF technology, reports of problems with the otherwise excellent HD DA 16-85mm come along more often. Even some buyers of this lens new have had to return it more than once to get a good copy. So far, the HD DA 20-40mm Limited certainly has a fine record of dependability. These are two lenses of which functional problems seem comparatively rare, in terms of complaints showing up here in PF. But even these do not have an absolutely perfect record.
The older SDM lenses are a very different story. And some of these, which are very expensive, cannot be converted to screw-driven! This would be extremely frustrating, having parted with such a high cost only to have the AF conk out, and then having to face a very expensive repair for a new replacement part also subject to this failure!
So far, apparently like thousand of others, I have been very fortunate with my DA 18-135mm in particular, as I have had it for over 10 years, using it on numerous camera bodies, and it works today as well as it did when new. Maybe even better with the latest camera bodies. In fact, I have right along noticed its AF to be exceptionally fast and accurate among the lenses I own, even when used on some cameras not well-regarded for very good AF performance- like the original K-5. I am very careful with my gear, but if this lens should ever develop failure, which I do not expect to happen, I would replace it for sure with another new one. It is that good.
Another thing to consider- when buying used- one never knows what this item has been through. Resultant problems after some trauma or other might not show up until much later.
Any mechanical automation comes with some degree of increased chance for problems developing. Perhaps this is why Pentax has been insistent in sticking with the old screw-driven AF technology in their premium Limited series of prime lenses, with the rare exception of the new DFA HD 21mm f/2.4 DC Limited.
Last edited by mikesbike; 03-10-2023 at 04:39 PM.