Dirty Scanner Optics

We rightfully assumed it should be due to dirty internal optics, and had the scanner cleaned at Nikon service center (the store paid $250 for this job). The scanner now works like new:

Note: this scan was adjusted in Photoshop for best appearance. Then the scan obtained previously on dirty scanner was adjusted separately, trying to match shadow detail to the normal image (shadow detail in the upper left corner) and reach similar overall look. These were scans from the same slide.

Though the Nikon example above is truly horrible, all brands of desktop film scanners are susceptible to dust problem. To keep them from degrading image quality, you may do these steps:

• If the scanner is not used constantly, store it inside a clean plastic bag between periods of use. This is what I do, at least. Note that you don't have to disconnect the cables from the scanner while it is in the bag, but you must switch it off. The bag blocks ventilation and the scanner may overheat (and even catch fire) unless you make sure it is off, preferably by disconnecting its power plug.
• Always store unused scanner accessories, e.g. film adapters, inside clean plastic bags.
• Pack the scanner into a plastic bag for shipment and storage. Do not install and operate it in a disty environment.
• Do not blow air into the scanner trying to clean it. This will only put more dust inside unless you see exactly what you are cleaning (may require opening the scanner).
• For Nikon scanners, position the scanner horizontally. This way, the surface of the mirror in the scanner is vertical and thus gathers much less dust (thanks a reader for the tip).

Quality and cleaniness of scanner optics is more critical than that of camera lenses. That's because the image on film has much larger contrast range than the original scene. A contrast range of 1:50 in the original scene may be mapped into a density range of 1:1000 on the slide. This makes the slide more vulnerable to flare in scanner optics.
 

Milder examples that may help you recognise problems

This resulted in soft look. This is not necessarily bad for portraits. With slides, you could use soft filters on the lens and get effect similar to flare in dirty scanner optics. There is, however, no physical equivalent of the flare effect obtained with negative scans.

Yes, this is unfortunate owner of the scanner - my friend Albert Lysko - on the picture. He and his wife were only scanning negatives and didn't notice anything wrong until I came to scan some of my slides.

The next two fragments of negative scans were sent me by Scott Squire (ssquire@mail.cmsfq.edu.ec) from Ecuador. When he eventually disassembled his Nikon LS-2000 (bought used), its optics looked dirty: "The mirror looked like it had been sitting inside a range hood in a kitchen", despite that the scanner was "...represented as being all-but new. I.e., the guy said that he'd taken it out of the package to be sure it worked, then never got around to using it". Scott cleaned the scanner himself.

Another example, with before and after scans (scroll down).

With slide film, you should look closely at dark parts of the image adjacent to bright objects. Make sure your monitor is properly adjusted, or you may not see the dark tones. If your room is brightly lit, it may also hamper viewing dark parts of the image (essential for some examples below).

Now that you've seen few examples, can you tell by this image if those PhotoCD operators did bother to keep their scanner completely clean? I feel they didn't.

There actually is another kind of flare not related to scanner optics and dust - CCD leakage. Bright areas on slides and dark areas on negatives smear along the CCD line, i.e. along the short side of the frame only. CCDs in old models of scanners were prone to it. This is a PhotoCD scan from slide (I call this particular slide "Scanner's death" :-). Flare on this scan is a combination of short halo around white area (scanner optics, probably) and CCD leakage, very noticeable in the dark sky above the white balloon. There was no flare on the original slide. The lab sucked, anyway. Another example of CCD leakage (on CanoScan FS2710).

There may also be defective pixels in your CCD, dust laying on the sensor or some other kind of irregularity in the CCD line. In this case, streaks run across the image along the scan direction, i.e. parallel to the long side of the frame. See examples (from Minolta Dimage Scan Dual II, Acer ScanWit 2720S and some flatbed scanners). Nikon has advice on how to recognize the cause of streaks. Streaks can be also caused by dirt in other parts of the optical system, e.g. on the illuminator bulb (scan from Minolta Dimage Scan Multi, medium-format slide).

The cause of irregularities running along the scan direction may be not acquired defects, but characteristics of the sensor and/or readout electronics. If you look at the large version of the photo to the left, you can notice vertical bands in the sky and in the dark water (look carefully... the bands may be barely noticeable). This scan has been made on a good Nikon LS-2000 scanner, but had to get shadows brightened a lot for the proper look, thus exposing the slight periodical irregularities in the sensor sensitivety. These bands may be caused by the readout process, but I don't really know. With an older and cheaper HP Photosmart scanner, a problem of this kind is much more visible.

Still not sick of scanning artefacts? Check Small ghosts (Nikon LS-4000/ Kodak E100S) | Yet another halo (Nikon LS-30/ Kodachrome). Send me more problem scans. For those of you completely paranoiac, read about grain aliasing.

If you scanner is not listed above, this does not mean it is free from these problems. They are inherent to the desktop scanners technology, and not necessarily can be eliminated by a proper design.

In the end, I hope this article wouldn't put you off scanning your pictures. Look at imperfections realistically.

P.S. If you still can't tolerate any compromise whatsoever, you can always have drum scans done of your slides (very expensive but near-perfect).

Thank you very much for your explanation about "dirty scanner optics". I had the same problem. I have a Coolscan LS-2000 and when I scanned my films and slides everytime I had flare. Looking for this problem at Google I found your page and then I knew what's the problem. This morning I called Nikon Service Center in Spain, where I live, but they didn't say me how much it costs me the cleaning of scanner. So finally I opened the scanner. It had a film of dust over the mirror and I cleaned it carefully. Now the scans are perfect. The operation took me one half hour and I saved the cost of reparation.

You can visit my Web page and see there are many images with this problem, that I tried to correct with Photoshop. I will re-scan these images...

-- Fran Fernandez (franlance@menta.net), November 22, 2001

Thanks for the article. It helped me to diagnose my deteriorating scans with my LS-2000.

I followed the Camera911 instructions and cleaned the scanner myself. It turned out that a dirty bottom mirror was the culprit. After cleaning, the scanner scans like new.

Here's a tip. Don't position your LS-2000 vertically. This allows any dust and dirt entering through the slide/negative adapter to drop onto the mirror. Position the scanner horizontally, so that the door slides left to right. This way, gravity won't work against you.

-- Gary Jean (gary.jean@us.army.mil), February 18, 2003

• Nikon LS-2000 cleaning - step by step guide to disassembling and cleaning a Nikon LS-2000 scanner. -- added by Don Doucette (camera911@cogeco.ca) in August 2002

  VM's comment: I had a chance to clean my friend's Nikon LS-2000 scanner. It was not very difficult, but I had to be careful. To gain access to the mirror, the scanner had to be half-disassembled, which took a couple hours. The article forgot to mention that a pretty small cross-type screwdriver was needed to remove some of the little screws. If you don't have the proper tiny screwdriver, you may fail to gain convenient access to the mirror.
  Indeed the only piece of optics that gathered much dust was the bottom mirror, because it was open and faced up. Blowing air was insufficient, and I had to contact clean it (breathed on and very, very carefully wiped by lens paper, taking a new sheet for every wipe etc.). The mirror was recessed and access to its surface was a bit tricky. It helped a lot that I've cleaned optics this way many times before, otherwise I would probably have damaged it or put a smudge or scratch on the nearby lens.

• Comparison of scans from HP Photosmart and Leafscan 35 by Joshua Martin.
• Nikon LS-5000 cleaning - illustrated step by step guide. -- added by Dennis Green (dennisgreen@comcast.net) in August 2004
• Before and after scans from Nikon Coolscan IV ED scanner cleaned by Tony Egan.
• Nikon LS-2000 lubrication guide (PDF, 530 KiB) by Phil Lee (silicontundra@yahoo.com), a very detailed step-by-step guide on how to re-lubricate the mechanism if it dries up and gets stuck. The inability of the scanner to move the mechanism (be it for the lack of lubrication or for other reasons) is manifested by fast flashing light on the front panel of the scanner. The scanner calibrates the mechanism by moving it back and forth immediately after being switched on; it’s at this time the fast flashing light can occur.