MRP(OPCSDEFS)           Optical Printer Control System          MRP(OPCSDEFS)

    NAME
        mrp - maximum ramp pulses for shutter motors

    USAGE
        mrp [chan] [pulses]

    EXAMPLES
        mrp b 800     # limit pro ramps to no more than 800 pulses
        mrp c 500     # limit cam ramps to no more than 500 pulses
                      # during shutter runs

    DESCRIPTION
        Sets a maximum for the number pulses used for ramping during
        shutter runs for the specified channel. Set this value equal to
        or less than the number of pulses it takes to move the exposing
        shutter from the 'closed' position to the position where the
        shutter just begins to open.

        This will ensure motor ramping does not occur while the film
        is being exposed.

        Use the following logic:

            If there are 2000 steps per full rotation of the shutter, and
            the shutter starts opening at 90 degrees (1/4 rotation) on
	    either side of the closed position, ramping can therefore
            occur up to 500 pulses without risking unintended film exposure.

        In actual practice, you may want to set the value slightly lower,
        in case the shutter has slop.

        Only channels with a shutter blade (camera, cap shutter)
        need an MRP value; the rest can be 0.

        To accurately calculate the MRP value for the camera, one must
        understand exactly at what point film exposure takes place, e.g.

            Shutter               5000   2000
            Exposure     Degrees  PPR    PPR
            -----------  -------  ----   ----
             Full Close   0       0      0      __
            First Light   76      1056   422      |   Film Exposed to light
              Full Open   112     1556   622      |__ during this period.
             First Dark   245     3403   1361     |   Avoid motor ramping
              Full Dark   283     3931   1572   __|   during this time!
             Full Close   360     5000   2000

        So for a 2000 PPR shutter, we want to limit motor ramping
        to the 0..400 and 1600..2000 region, to avoid ramping during
        exposure. Therefore the MRP should be 400, which limits rampup
        to the 0..400 region, and rampdown to the 1600..2000 region.

        In actual practice there's slop in both the home and shutter
        movement, but also the "First Light" and "Full Dark" are not
        very critical, as very little exposure is happening during
        this time, so often MRP 400 can safely be 500 (or 90 deg).

        For camera MRP, it's the degree positions of the shutter blade
        which determines when light can first start hitting the film
        through the Acme 35mm full frame aperture. The formula for
        degrees(out of 360) to pulses (out of the PPR or Pulses Per Rev):

                 pulses = ( <deg> / 360 ) * <PPR>
                 1056   = (  76   / 360 ) * 5000    <- for a 5000 PPR shutter
                  422   = (  76   / 360 ) * 2000    <- for a 2000 PPR shutter

     CAVEATS
        MRP also affects the operation of AUTOFILT(OPCS) and FILTER(OPCSDEFS).
        See these documents for details.

    SEE ALSO
        MRP(OPCSDEFS)     - set 'maximum ramping pulses' for shutter runs
        RAMP(OPCSDEFS)    - set maximum accelerations and velocities
        SPD(OPCS)         - set the camera's exposure speed
        SPD(OPCSDEFS)     - set a motor's running speeds
        AUTOFILT(OPCS)    - enable/disable the auto-wedging filter wheel
        FILTER(OPCSDEFS)  - define channel to control a filter wheel

    ORIGIN
        Gregory Ercolano, Los Feliz California 08-15-91