How do they focus

Discussion in 'Scanners' started by pgjönsson, Jan 9, 2006.

  1. pgjönsson

    pgjönsson Guest

    I am considering an HP 4890 photo scanner for use with my XP computer,
    scanning particularly 6x6 cm positive transparencies , but wonder , can
    the machine focus through glasswindow and some airgap up to the film and
    yield a resolution up to 4800 dpi.
    Would appreciate comment from someone who has used it for this purpose.

    pgjönsson, Jan 9, 2006
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  2. pgjönsson

    pgjönsson Guest

    Carl, I have never thought about the ´how´before, but to experiment I
    put a measuring tape on the glasswindow of my old Primax 9600 Profi
    flatbed, inclined about 45 degrees with zero on the glass proper and
    ofcourse millimeter and centimeter scales facing down. Scanning revealed
    that I could read centimeterfigures up to 10,( 4 inches) and more roughly,
    from the scanning head getting quickly very low with increased distance
    from the glass, and millimetermarks up to a hundred + but as expected being
    more blurred with more distance from the glass.
    Now I wonder, when a manufacturer claims ,say 3200dpi, is that with an
    object laying flat on the glass-surface or does that include the ( small)
    distance from
    the glass to the object when a transparency, framed or in a ´holder´ is
    I think this is a question someone who is manufacturer-related should
    the thread maybe could be expanded further in this direction.

    regards / per
    pgjönsson, Jan 12, 2006
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