What could cause vertical lines in scanned photos?

Question

My CanoScan 8800f has recently begun introducing vertical lines in all my scans. I believe this started occurring after I had removed the top cover multiple times to clean the dust from the underside of the glass (and then several more times to remove stubborn streaks). My guess was that some dust got stuck to the imaging components inside, so I took the cover off the actual scanning mechanism and hit the inside with a good blast compressed air. Even after all that, I still see these vertical lines along all my scans.

What could cause this and what can I do to resolve it (if anything at all)?

Answer 1

I also suspect that there is something inside your scanner interfering with scans.

Since the defect follows the direction of the scan, the problem is probably located on the scanning unit (not the glass).

For scanners that use CIS (contact image sensor), it could be located on the "light conductor" that is in near contact with the scanning surface. For scanners with CCDs, the problem could be on any of a number of mirrors or on the lens in front of the sensor.

If you've ever detached the glass from the scanner housing, you might have put it back with the wrong side facing the sensor. The glass could have coatings on one side that are needed to prevent reflections from interfering with the scan. Similarly for any other components between the sensor and the target.

Answer 2

Many scanners have a white calibration strip to calibrate the sensor before scanning. Dirt on the strip results in vertical lines. Usually, the dirt got there during maintenance or transport.

See also: Fixing Vertical Lines on a Scanner.