A problem with most anti-shake systems is when there is very little shake, noise in the sensor system actually jitters the sensor around and can create an artificial "shake". Though small, it can lead to blurry pictures when they are examined under magnification. That's why it's best to turn the anti-shake off when using a tripod. It's somewhat like a person that experiences ringing in the ears (tinnitus). It decreases when the background sounds are louder but becomes a problem with total silence.
Woe to me as well, I forgot to do that when shooting some 500mm shots on a tripod recently (first time with my K-1 and the 500mm), and the photos looked like the camera was shaking when I magnified them. At first, I thought the lens had a problem, but then I remembered what I did and since have done some crisp shots without the anti-shake turned on.
Last edited by Bob 256; 05-11-2017 at 08:29 PM.