Some Canon EOS-1D/1Ds Mark III digital SLRs may show ring-shaped spots on the image caused by oil lubricant on the surface of the low pass filter (LPF), located in front of the CMOS sensor. To address the issue, Canon USA has issued a service notice to affected users to contact their Customer Support Center and arrange free cleaning of the mirror box to remove the excess oil.
These ring-shaped spots are the images of oil lubricant on the surface of the low pass filter (LPF), which is located in front of the CMOS sensor.
This oil is used inside the Mirror Box to lubricate some of the camera’s moving parts. If the oil is applied too liberally when the camera is manufactured, it can become scattered onto the surface of the LPF through normal camera operation.
If you own an affected Canon EOS-1D or 1Ds Mark III Digital SLR, Canon will be happy to service it back to its pristine condition for free.
[Site: Canon USA]