Thoughts on Theory and Practice of Scanning (Archival/Forensic)

Discussion in 'Digital Darkroom' started by jdm_von_weinberg, Sep 28, 2016.

  1. I'll throw in my thoughts on the subject for free.
    1) Epson flatbed 'film-scanners' just aren't the sharpest. They throw out lots of pixels, but not half as much detail. Their scans should be easily beaten on sharpness and detail by a good print 10" x 8" done on glossy paper.
    2) If the flatbed scanner's focus is adjusted for its filmholder(s), then the focus on the glass platen will be less than optimal, and vice versa.
    3) Even allowing for sub-optimal platen focus; the extra magnification of a 10" x 8" print should more than compensate and give a detailed scan from such a print.
    4) Most proper, dedicated (i.e. not a flatbed) CCD film scanners of modest specification (3200~4000ppi) are easily capable of grain-sharp scans. Most flatbeds aren't.

    Why, then, are your scans from prints not sharp?

    The obvious culprit would be prints that aren't grain sharp to begin with, and this could be due to poor enlarger alignment, vibration during exposure, a poor-quality enlarging lens, or poor focus. All areas for scrutiny.

    Poor scan quality from a pin-sharp print can really only be due to poor scanner focus at the platen, or possibly a lack of contact of the print with the platen.

    Obviously, these are things that can't easily be diagnosed at a distance without seeing the setup, or any results thereof.

    FWIW. Some time ago I did a comparison of a 600ppi flatbed scan of a 10x colour print (effectively 6000ppi), with a direct 2700ppi scan of the negative. The detail in the print-scan was superior. I would expect a direct scan from a 4000ppi filmscanner to be much closer, as is a 24 megapixel digital camera copy of the same negative.

    Scan-Copy_comparison.jpg
    FILE119.JPG
     
    Last edited: Jul 13, 2019
    invisibleflash likes this.
  2. Thanks, Rodeo_Joe.

    Also in the "controls" look for what resolution is set for the print scans as opposed to the negative scans. I don't know the Epson, but these could be set to different resolutions on my Canon scanners.
     
  3. Some Epson scanners, I believe the 700/800 series use two lenses and focus points:- One for prints which sit flush against the glass. The other for film that sits above the glass in the film holder. I believe the V550 use one lens and focus point. But checks the specs to verify.
     
  4. I'm surprised that the camera copies aren't better than they are. And by why you're not using flash to obviate any vibration.

    From the picture of the film reel, it very much looks as if there's too much diffusion on the copy lamps, and that they're set at a steeper angle than 45 degrees, or are set too close to the copyboard. Any of those things will result in low contrast and/or emphasis of surface reflections and imperfections from the artwork.

    Used as shown, that book copier is going to give pretty poor copies, due to page curvature and shading or surface reflections. The only way to do the job properly and without damage to the book, is to press each page under a sheet of glass, and possibly backed with black paper to reduce print-through. Trying to flatten the whole book under glass is almost certain to break the spine or cause other damage to a delicate folio. So each page must be carefully flattened separately for truly archival reproduction. Not just plonked under a supposedly purpose-made camera and light source. That might be alright for a quick OCR of a cheap modern paperback, but not for any remotely valuable MS.
     
  5. As someone who lived through the bad old days before ready access to flatbed scanners, and even before they were invented. I can't help thinking that camera copying got a 'bad rap' in Daniel's comparison, as linked above.

    After all, camera copying was all we had for a long time, and there was never a question of it giving inferior quality.

    Anyway, I thought I'd balance the picture (pun entirely intended).

    I found an old framed photo of my father's WWII army platoon - few of whom survived the war, sadly, but that's another story. The print was slightly silvered at the edges, quite badly rippled and must have been creased before framing. In short, not in very good condition.

    After removal from the frame I did a flatbed scan of the print. It didn't scan too well due to the rippling.
    Flatbed-full.jpg
    Here's a crop of the most problematic area.
    Flatbed-scan.jpg
    There's reflective flare off the undulating surface, and the cracked surface shows up noticeably.

    OTOH, the camera copy fares a lot better.
    Camera-no-frame.jpg
    The surface flare is completely gone, and the silvering presents no issue.
    Here's the same area that the flatbed had difficulties with.
    Camera-copy-noframe.jpg
    No retouching was done on either copy, apart from improving the tone curve.

    So, my findings are the opposite of Daniel's. The camera copy is clearly better than that from the flatbed scanner, and maybe a touch sharper as well.

    FWIW, the camera setup consisted of a tripod with cross arm. Camera; Nikon D800 with 105mm f/2.8 AF Micro-Nikkor. Lighting; two SB-25 speedlights on stands about 4ft from the artwork and at a 40~45 degree angle. Speedlight 'zoom' setting was 50mm and no diffuser was fitted. Room lighting was turned off during copying to avoid spurious reflections.

    Flatbed scanner was a Canoscan 9950F. Scanned at 600ppi.
     
    Last edited: Jul 15, 2019

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