Enlarger lens options.

Discussion in 'Darkroom Developing and Printing' started by otzi, May 7, 2008.

  1. I know F.E.Ives used special treatment of the negatives, and careful control
    of their condition for best results. They did not have litho film in those
    days. They do now (for a while more, at least), so I make contact prints of
    the soft-dot stuff onto another piece of litho film and that makes
    hard-dots. Exposure is tricky at first, because if you change the exposure,
    you change the diameter of the dots. I make some 50% dots (my densitometer
    will measure % dot area) and make the contact prints 50% also -- or pretty
    close anyway.
    Jean-David Beyer, May 11, 2008
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  2. Yes, the screens are angled to prevent moiré.

    By the way, the standard screen angles for 4-color (CMYK) printing are:

    K (black): 45°
    M (magenta): 75°
    Y (yellow): 90°
    C (cyan): 105°

    So far as I know, these have been in use as long as 4-color halftone
    printing has been around.
    David Nebenzahl, May 12, 2008
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  3. Interesting explanation of screen angles can be found at
    http://www.dtp-aus.com/hlftone.htm (scroll down to "Screen(#) Ruling
    and Angles").

    Interestingly, it's not just a matter of reducing moiré effects; the
    screen angles are selected to create "rose" patterns which, apparently,
    are the least bad alternative (there will always be some kind of pattern
    generated by multiple halftone screens, and this is thought to be the
    most pleasing one).
    David Nebenzahl, May 12, 2008
  4. Brings back memories ... My firm designed a graphic arts exposure
    integrator that had exposure adjustment in % dot gain (along with
    stops, OD (for step-wedge test results), and straight %). Then
    we designed nuVac for stochastic screening and the hell with
    dot-gain. All about 20 years ago ... the dénouement of analog
    Nicholas O. Lindan, May 12, 2008
  5. I just use a Macbeth densitometer TD-901 that has a %dot scale.
    Jean-David Beyer, May 12, 2008
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