White spots on scan of holder with no negative

[jackbaty]

I let Vuescan keep going a bit long after it finished a half strip of 35mm (HP5+) and the "blank" scans were filled with white spots. I've dusted all class scanning surfaces and still get the spots so I find it hard to believe it's all dust. Could this be some sort of artifact from scanning an empty holder?

 

[silverbullet]

do you use a scanner with a mirror for guiding the rays from the negatives like a Coolscan 4 from Nikon?
In this case it might be some particles which are on the surface of the mirror.

In my case there was dust after some years of usage. From the net I got the hint to put the scanner on the side in order for storage to get the thin mirror glass upright without a surface.

 

[jackbaty]

It's an Epson V750. Sorry I should've mentioned that.

 

[tlitody]

dust on sensors

 

[jackbaty]

Wouldn't dust on the CCD cause streaks rather than spots?