I have been through 3 Pentax ist Ds since 2003 and am quite familar with the camera, especially with the potential for the sensor to get dusty when changing lenses (I've had major issues with that.) Now I have a new ist D with a 28-300 Tamron lens, and to prevent this dust problem, I took it to my camera shop where the lens was installed on the brand new camera with all the components in a plastic bag to protect against dust. Once the lens was mounted, I shot four test photographs to ensure there were no spots. The images were clean...what a relief! I'll never change the lens or even remove it as long as I own the camera. Now the camera is about three weeks old and has about 500 exposures. I have started seeing what looked like dust specks--impossible since the lens has never been removed, right? Back to the camera shop to shoot test pics in the same location on F16 at the same time of day, though the sky was not exactly the same, of course. Definite spots, and, with ISO at 400 and no low light situation (afternoon sun!) you'd think there'd be no noise, right? This camera is always around my neck or stored in the bag. I keep my equipment clean and in good condition. My photo shop is well-versed with years of experience, and they are COMPLETELY stumped--and broken-hearted-- that the issue continues.
So, has anyone experienced this? Is it dust (how can that be possible if I've never removed the lens?) Is it noise (and if so why does it look like dust?) I'll be happy to email you the test pics. I definitely need help on this, and of course I'm contacting Pentax too.
My friends who are shooting Canon are NOT having this problem.
This is also posted on Pentax group.