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Thread: Why do most scanners scan larger negs at lower resolution?

  1. #11
    Randy Moe's Avatar
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    Re: Why do most scanners scan larger negs at lower resolution?

    Thanks Sandy for the definitive scanning answer.

    I plan to try V7XX 6.5x8.5 high res scans of 8x10's to compare results.



    [QUOTE=sanking;1061192]
    Quote Originally Posted by Sevo View Post

    The V700/V750 definitely has two lenses and the scanner switches based on which scanning area you choose in software. If you select film holder the scanner uses a shorter focal length lens and the maximum area that is covered by the lens is about 6.5 X 8.5". If you select film area guide the scanner switches to a second lens that is positioned farther from the CCD to cover a wider area, which allows one to scan a full 8X10" negative. The lenses are probably not very different in optical quality, but the closer you place a lens to the CCD the higher resolution you can get. Imacon/Hasselblads and the old Leafscans do the same thing, position the lens closer to the CCD to cover small format media, farther away to cover 4X5. For example, with the Leafscan 45 it was possible to scan a 35mm negative or slide at 5400 dpi, medium format was only 2400 dpi, and 4X5 was 1200 dpi. The Imacon, which was probably based to some extent on the design iof the Leafscan, uses a similar method of zooming. It is rather like the concept of using an enlarger, the closer the lens and film is to the baseboard, the higher the resolution on paper.

    The Eversmart/IQSmart scanner use a high quality lens placed very close to the CCD and scan in rows, like mowing your lawn, then the files are stitched in proprietary software. This is called XY scanning. Cezanne scanners will also do XY scanning, but there is no stitching in the software so you have to do that yourself after the scans are made.

    Sandy

  2. #12

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    Re: Why do most scanners scan larger negs at lower resolution?

    Here's an oversimplification to illustrate the point: CCD scanners are generally measured in total pixels across their "bed". If you have a 4000 ppi scanner, and you have a 1 inch piece of film, you can get 4000 ppi. However, if you have a 4 inch piece of film you get 1000. The number is the total pixels.

    You also have to take into account the optical resolution, which is different from the amount of pixels something is capable of generating. These are often mixed up. You don't get 8,000 ppi of optical resolution in the X5, it's somewhere between 2 and 3, I would imagine, close to 3.

    Drum scanners take one sample at a time, and so when there is a 4x5 piece of piece of film and its generating 4000 ppi, then its 20,000 total pixels (on the long edge).

    Lenny
    EigerStudios
    Museum Quality Drum Scanning and Printing

  3. #13

    Re: Why do most scanners scan larger negs at lower resolution?

    Quote Originally Posted by Lenny Eiger View Post
    You also have to take into account the optical resolution, which is different from the amount of pixels something is capable of generating. These are often mixed up. You don't get 8,000 ppi of optical resolution in the X5, it's somewhere between 2 and 3, I would imagine, close to 3.
    Lenny, can you please expand on this? This quick visual comparison suggests it's certainly above 4 (thousand):


  4. #14

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    Re: Why do most scanners scan larger negs at lower resolution?

    So, you have line-pairs in your eyes? That looks like 4,000 to you? Maybe it is, they can do much better with 35mm, apparently around 4k. That's under the right circumstances. However, I'm not really interested in expanding. I was trying to answer a different question and I don't want to diss anyone's scanner or get into pissing contests. If you are happy, then all is good.

    Lenny
    EigerStudios
    Museum Quality Drum Scanning and Printing

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