Originally posted by Tom S. As I have repeatedly pointed out, the longer fixed focal length lenses are undoubtedly used less often than the more popular zoom lenses, thereby sitting idle more often, yet the reported failure rate for them is lower. Care to explain that?
My speculation: the element group being moved in them
is lighter than in the more troublesome zoom lenses.
Unfortunately, as I hinted in my earlier reply,
none of us know the answer,
so all we can do is hypothesize.
Sadly, Pentax seem to be as helpless as we consumers are.
But at least we can use the collective wisdom of this forum
to try to gather some impressions.
One of those impressions is that disuse worsens the problem,
and not just through allowing electrical discharge.
It may be some grease hardening,
or it may be some other effect.
My own market response has been to avoid SDM lenses.
I bought 58/1.4 and 90/3.5 Voigtlaenders instead of the 50-135/2.8,
and a Tamron 17-50/2.8 A16P instead of the 16-50/2.8.