Minimizing Moire patterns when scanning large format negatives???

Discussion in 'Digital Cameras' started by Terry Smith, May 22, 2006.

  1. Terry Smith

    Terry Smith Guest

    I'm a large format photographer using an Epson 4870 scanner to scan my 5x7
    negatives. I've had a custom 5x7 carrier made to hold the negatives (similar
    to the 4x5 transparency carrier that came with the scanner). In general,
    this setup work quite well, but I'm getting moiré patterns, especially in
    the middle of the negatives where there is a lot of single tonality area
    (like open sky) mostly on B&W negatives.

    Does anyone have a clue on how to minimize this moiré pattern problem? (and
    no, I'd rather not send my negs out to be drum scanned... <s>)

    Terry Smith, May 22, 2006
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  2. Are you sure it's not Newton's rings? Is the film touching the glass? My
    experience with the 2450 was that Newton's rings was a nasty problem, but
    the 4800 ppi Epson scans I've seen would lead me to doubt that Moiré would
    be an issue.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 22, 2006
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  3. Those aren't "moire patterns", they're Newton's rings. They're caused by
    interference between re-reflections of the image across the airspace between
    an imperfectly flat negative and an imperfectly flat piece of glass (both
    of which are more or less inevitable).

    If you dare, the most effective way to address these when scanning is to
    coat the negative with special oil. Then you'll just have to clean it --
    and your scanner -- before you use it for anything else...

    Oil immersion is still standard practice when doing high-resolution drum
    scans, I believe.
    Thor Lancelot Simon, May 22, 2006
  4. Terry Smith

    Jim Hemenway Guest

    Hi Terry:

    I agree with the others... I think what you are seeing are Newton's
    rings, which do look somewhat like round moiré patterns.

    I shoot 11x14 Ektachrome and scan it on an 11x17 Epson 836XL with the
    transparency top.

    At first I couldn't get quality scans because the film wasn't flat
    across its long side. So I added another piece of glass on top of the film.

    This has worked well except for the appearance of very tiny Newton's
    rings... and it's a real pain in the neck.

    After trying shifting the film, and trying thin paper "lifters" between
    the glass, as well as trying the messy oil used with drum scanners, I
    found that it is impossible to avoid at least a few rings

    So, the best way for me to remove the rings, is with both the cloning
    tool and the healing brush in Photoshop.

    Jim Hemenway, May 22, 2006
  5. Terry Smith

    rm Guest

    Try scanning the negs with emulsion to the glass, then flip the image in
    rm, May 22, 2006
  6. Terry Smith

    Terry Smith Guest

    How do I keep the negative flat on the glass?

    Terry Smith, May 22, 2006
  7. Terry Smith

    Terry Smith Guest

    David, Thanks for the correction. I'm sure they are Newton's rings; I don't
    know why I called them Moiré patterns...
    Terry Smith, May 22, 2006
  8. Then all you have to do is keep the film off the glass.

    Which would be, I'd think, quite hard. Sigh. (In my experience, the emulsion
    side down trick doesn't really work.)

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 22, 2006
  9. Terry Smith

    Terry Smith Guest

    I had my custom 5x7 carrier made out of 4 ply flat black matte board.

    Would a thicker matte board (or some other material) lessen the chance of
    the film touching the glass? If so, how does the scanner know where to
    Terry Smith, May 22, 2006
  10. The Epson flatbed's don't focus. You need to test for optimal focus, and
    hold the film at that distance above the glass. The new V700 (or V750)
    provides means for doing that.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 23, 2006
  11. It looks good on paper. (My theory is that film really doesn't have any more
    than 2700 ppi of real, usaable information on it, so the Epson scanners
    (which only have effective resolutions about 1/2 their claimed resolution)
    should be getting close to getting everything that's there.)
    Both of the above. It's 8:12 am right now. (Also, I work at home, so unless
    I'm out bowling, I'm probably in front of the computer.)

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 23, 2006
  12. Terry Smith

    Terry Smith Guest

    How does one test for optimal focus? By trying dozens (or perhaps hundreds)
    of heights above the glass? And how does one do that? With increasing
    numbers of individual sheets of paper?

    This scanner world is getting pretty difficult...
    Terry Smith, May 23, 2006
  13. I'll average 200 or so on a good day. Don't ask about the bad days.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 23, 2006
  14. Terry Smith

    Terry Smith Guest

    Already did that with a Nikon D2X, but I still LOVE large format
    photography. As good as a D2X is (or a 1Ds Mark II), there's something
    about a LF neg...
    Terry Smith, May 23, 2006
  15. Although I'm from Boston, I've never even seen duckpins, even on the tube.
    Are there any duckpin lanes outside New England?

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 23, 2006
  16. Terry Smith

    Terry Smith Guest

    Thanks Kevin. This has been recommended (as well as argued against) as a
    solution, but heck, I'll give it a try!

    I used to experience a similar problem. In the center of my negatives,
    I would get what looked like almost an oil immersion effect. Really
    annoying. I solved the problem by flipping the negative over so that
    it curved in the opposite direction (If you looked at the negative
    end-on, the short egde was curved up, like a smile. That's when I
    would see the problem. When I flipped over the negative such that the
    short egde looked like a frown, that's when the problem would go away).

    Terry Smith, May 23, 2006
  17. Often the optimal focus for transilluminated film is in the order of
    0.5 - 1.0 mm above the glass platen (to accomodate mounted slide film)
    and there are usually holders for other film (sheets/strips) that also
    position the film at about the same height.

    So all it takes is something as simple as a wooden match stick, wood
    because it won't scratch the glass and it has some structure, with one
    end resting on the glass and the other end raised by a known/measured
    height above the glass. If the best focus is e.g. halfway the stick
    then optimal focus is at half the height.

    More elaborate methods can be used, but there is also a certain depth
    of field that can be exploited. As long as the film is held flat,
    everything is at the same level of focus accuracy.

    Bart van der Wolf, May 23, 2006
  18. Hehe. You've found the crux of the matter; everything looks somewhat fuzzy.

    What I ended up doing was putting a nasty scratch in a frame (to have a nice
    sharp edge to image) and scanning that frame at an angle.

    What Bart said.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, May 24, 2006
  19. Terry Smith

    Jim Hemenway Guest

    Hi Bob:

    They vary between 260 and 280 megabytes. That's as 8 bit at 800 dpi as
    Photoshop .psd files.

    Here's some which I had in a large format group exhibition in
    Springfield, MA in April.

    Jim Hemenway, May 26, 2006

  20. Who's got the time or energy for that?

    All scanners have focus issues, and really the
    only way to definitively avoid these is with wet
    mounting, and even with wet-mounting, an
    Epson flatbed is not going to hold up against
    a drum scanner or a Nikon MF film scanner.

    I've never seen a perfect film holder, either
    for an optical enlarger or for a film scanner.

    Vincent Oliver has scan snippets at photo-i
    comparing LS-9000 vs. Epson V750 on MF film.


    There's no telling from the snippets on my site
    whether a given sample has optimal focus or not.
    In one or two submitted samples, I suspect not.

    For my own, I would say yes, they're "critically
    focused." With the Nikon, you can generally
    get critical focus at least on one point on the film.

    Ie., the Nikon has a focus servo like a proper film
    scanner should. I never claimed that the focus was
    uniformly excellent from corner to corner.

    rafe b
    Raphael Bustin, May 26, 2006
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