Originally Posted by
JohnRostron
Thanks to Mark and Izzie for spotting the spots. I tried photographing a nice plain surface (a blank screen!) and I could clearly see the bottom spot, but I could barely see the upper one. I then cleaned my mirror surfaces (front and back) with an airbrush. (The Sony A55 has a translucent mirror which stays in place.) I figured they could have been dust motes on the mirror. I also went through the camera's sensor cleaning procedure and then repeated the plain surface photos. No sign of any spotting now!
I think the reason I have not noticed these before was because, in most of my images, there has been a fairly varied image there, with little plain surface where spots would be noticeable. Once I used a uniform background I could see at least one spot clearly.
Izzie, I have been able to track down your Monitor Calibration Image from Dry Creek Photo (the source of your image above), complete with instructions!
John