User manual

25 • Focus adjustment and focus calibration
ColorQuartet 5.0 Pro
201
Guidelines for focus adjustment
For a list of which functions are supported by which scanners, see Focus & Aperture • Overview
• Transparencies only, emulsion side down: If all the images on the drum or mounting plate are
transparencies that are mounted with the emulsion side towards the drum/mounting plate,
the default setting found during focus calibr
ation will be sufficient to produce images with
optimal sharpness.
• Different types of originals on the same drum or mounting plate: If you are scanning some
transparencies emulsion side up and others emulsion side down, or if you are scanning reflec-
tion originals of varying thickness, use Autofocus to ensure optimum sharpness for each
image.
TIP:
After activating Autofocus and clicking on Ready to Scan, you can see the point chosen for focus-
ing by opening the job again and opening the feedback windo
w. The focus point is indicated
by a small cross.
• Rescreening: The best way to blur existing halftone dots is to use the digital D
escreen feature in
the Special Functions section of the Sc
an Setup window. However, it is also possible to defocus
the optical system mechanically if your scanner supports this feature.
For optical defocusing, set Focus Elevation to a value between 0 and –500. This moves the focal
point towards the drum or mounting plate.
The value depends on the original’s halftone screen. The coarser the screen ruling, the bigger
the dots, and the more the scanner must be defocused. You may have to experiment to find
appropriate levels of defocusing for various screen rulings.
Note the results for future reference.
TIP:
For best results, apply optical defocusing during preview scanning, rather than during the
final scan. This is because the highlight and shadow measurements, which are based on the
preview scan, are affected by the focus. If you do this, remember to reset the Focus Elevation to
0 afterwards!
• Avoiding graininess in smooth image areas: Some images include large, smooth areas of color
(for example, a blue sky) that may have a tendency to show the film grain if scanned at high
resolutions, due to the high resolving power of the scanner’s optics. To correct this effect in
transmission scans, one possibility is to set the Focus Elevation to about 20 for a flatbed scan-
ner or about 50 for a drum scanner. If you choose this technique, you should use little or no
unsharp masking, and avoid using the smallest aperture if you have a drum scanner. (Another