SDM failures horror stories

Sigma have only just announced a recall of several lenses for focusing problems.

But that's just it John - they've announced a recall i.e. Sigma will pay for the cost of fixing the flaw, not the customer. If Pentax had announced a recall of SDM lenses (rather than pretending the problem doesn't exist, as they have with the 16-50 and 50-135) then your point would stand, but they haven't.

It may be that a recall was unecessary because the fault was actually rare. The point is we don't know.

Sorry for delay in replying....

It fails to focus very occasionally, mainly at the long end, and makes an uncharacteristic noise, as I say it's quite rare so I haven't given it much thought

I believe it wasn't a batch off lenses that had a problem so Pentax didn't had the option to call lenses back.

Oh that doesn't sound too good, hopefully it's nothing

Mine's the same at long lengths and dim light. I think it's a characteristic of this lens - arising from the short focus steps apparently. If you rest a finger gently on the focus ring as it tries to find focus this solves the problem - it locks quickly and reliably then.

They could, however, have recalled all of them or (alternatively) announced a warranty extension only for SDM problems (like Microsoft did with the Xbox 360 RROD), which would have reassured potential purchasers while probably costing a lot less than recalling every 16-50 and 50-135 ever sold.