I can see spots on my images - what are they?
 
 
Microscopic dust particles on the imager surface/low pass filter will show up on the images. Dust can be quite intrusive.
 
 
Can the low pass filter surface be cleaned?
 
 
YES, we clean out the shutter and mirror box area using compressed air, then we wet swab the filter clean. 
 
 
Refer to link: CCD cleaning