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DSW700 System Description
Hardware characteristics
1. Basic design The DSW700 has at its center an extremely rigid base plate, manufactured as
a precision casting. This is supported on a frame, furnished with casters and stabilizers
(leveling screws). On the base plate are mounted precision steel rails, which derive their
flatness from the base surface together with a jack screw approach, which ensures
straightness before the rails are screwed tight in their final positions. Both X and Y stages are
milled from aluminum. A back-lit panel mounted on the lower stage enables the operator to
view a section of the film, for example to select a particular exposure for scanning. An
automated motor and cam arrangement raises and lowers the glass cover plate automatically,
under software control, to permit roll film to be transported. For cut film, the operator raises
and lowers this plate manually, at which point it behaves like a hinged lid.
2. Input media The stage accepts film transparencies, as roll film or cut film, or glass plates of
any thickness. The scanning format accepts images more than 260 mm square (10.2 x 10.2
inches). Input transparencies can be color or black and white and can be positive or
negative.
3. Servo drives The drive mechanism is a friction drive that provides excellent performance and
requires little maintenance. This design has been successful on all DSW models for the past
fifteen years. Modern precision positioning encoders with non-contact reading heads have
been selected for improved performance.
4. Stage accuracy The resolution of stage positioning at any point is 0.5 µm. The accuracy
threshold is a maximum 1.5 µm (0.00006 inch) root mean square error (RMSE) or better on
each axis, based on computer calibration and compensation. Stage calibration is provided
via automated grid plate measurement and is required infrequently.
5. Light source and optics The illumination system provides uniform overhead illumination
over the field of view of the CCD array sensor. The DSW700 uses an LED dome light,
supported in a stationary position above the stage plate. The dome consists of an array of
red, green, and blue LEDs, arranged in two concentric rings.
The new LED source is more economical, with a life expectancy of more than 10 years under
constant use. Most importantly, the use of LEDs in the DSW700 allows for a much more
efficient, substantially faster implementation of sequential color capture than in the past.
Flat bed scanners sometimes produce a phenomenon called Newton rings when the film is
not held perfectly flat between the pressure plates. Typically, they become visible in a color
scanned image as a rainbow series of light and dark rings around nondescript points in
homogeneous areas. Unless a special optical fluid is used to eliminate the air gaps and
therefore the index change between two media, Newton rings will usually form. The solution
in the DSW700 is to reduce significantly the formation of ring patterns by controlling one of
the contributing physical factors – the reflection coefficient of the surfaces. By suitably
reducing the amount of reflection between the glass pressure plates, it is possible to reduce
the ring amplitude until it is virtually invisible.
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