Originally posted by FJC 😯 I'm only a poor (but proud) k5 owner. No firmware update for me.
For the K-5 the Pentax firmware site lists the latest as:
"Changes to V1.16
Correspond to HD PENTAX-DA AF REAR CONVERTER 1.4X AW.
Improved stability for general performance."
Unfortunately there is no reference of the update being related to optimized focus operation for the FA Limited lenses (31, 43, 77mm HD or SMC variants). The earliest camera model for which Pentax specifically makes that statement begins with the K-3 original.
As a user of the K-5 classic (original) who was previously running V1.14 I have gone ahead and updated. Honestly, I would not usually expect a firmware update to make an obvious difference (I tend to think of firmware updates as more of a bug or issues fix). I have not yet tried the 43/77mm. I did use the DA 50-135mm and Sigma 17-50mm today with solid results. But that is to be expected as my particular K-5 was calibrated by Pentax service under warranty back in 2012 and ever since has performed with an impressively concise and repeatable AF without focus hunting issues.