FILTER(OPCSDEFS)        Optical Printer Control System         FILTER(OPCSDEFS)

    NAME
        filter - define the channel that controls the filter wheel

    USAGE
        filter [chan] [tvels] [vels]

    EXAMPLES
        filter h 8  4 10 16 20 20 16 10 4
	       | |  ---------------------
	       | |               |
	       | |               The 8 velocity samples sent to the motor,
	       | |               including ramping. Sum is 100.
	       | |
	       | 8 velocity samples
	       |
	       Channel with filter wheel

    DESCRIPTION
        This command defines which channel controls a 'wedge wheel', or
	'filter wheel'. These settings configure the AUTOFILT(OPCS) command.

        Most filter wheels usually have 20 filters. If the controlling motor
	is 2000 pulses per revolution, and the motor is geared 1:1, then it 
	would take 100 pulses to move the motor 1 filter position.

	    [chan] is the channel controlling the filter wheel.

	    [tvels] is the number of velocity samples specified.

	    [vels] are the velocity samples. These values are the
	    raw speed values (velocities) sent to the motor.  These values 
	    should smoothly ramp up then back down.  The sum of these values
	    should be the number of pulses to move to the next filter position.

	    These values are configured by hand, since the idea is to get the
	    motor to move to the next position in as little time (as few values)
	    as possible, without stalling the motor. At the fastest camera
	    speed, you will want the filter wheel to be at rest while the
	    camera is exposing film.

    NOTES
        When AUTOFILT(OPCS) is enabled, the filter wheel will begin moving
	after each camera frame exposes, at the moment the camera shutter
	has completely closed. This is determined by the MRP(OPCSDEFS) value.

	If you find the filter wheel starts its movement while the shutter
	is still open, you should either decrease the MRP(OPCSDEFS) value,
	or make sure your home position for the shutter is accurate.

	The following diagram shows the travel of the camera shutter through
	a full rotation, from left to right. The numbers indicate the pulses
	throughout the rotation of a shutter that is 2000 pulse per rev:


        OPEN --                    __________
                                  /          \
                                /              \
                              /                  \
      CLOSED -- ____________/                      \___________
               |           |           |           |           |
	       0          500         1000        1500         2000
	       
                                                   ^
						   Filter motion
						   starts here

	If MRP(OPCSDEFS) is 500, then the AUTOFILT command will begin
	moving the filter wheel at the 1500 position, ie. 2000 - 500.
	The shutter should be fully closed at that position.

	If you decrease the MRP(OPCSDEFS) value to 400, AUTOFILT will begin
	moving the filter wheel at the 1600 position, ie. 2000 - 400. 

    LIMITS
        There are no hard coded limits for the number of velocities.
	If the number of velocities exceeds memory, the interlal
	malloc() function will fail, reporting an error.

    SEE ALSO
    	AUTOFILT(OPCS) - enable auto-wedging with a filter wheel
    	MRP(OPCSDEFS) - maximum ramp pulses for shutter motors

    BUGS
        The autofilter stuff was broken for a long time until 2.34b.
	Before that, any kind of wedge wheel stuff had to be done
	with GO(OPCS) commands mixed into shooting.

	It's undefined what happens if the filter wheel vels take
	longer than the camera shutter's "closed period". Especially
	at the highest shooting speeds.

    ORIGIN
	Version K1.12e+ Gregory Ercolano, Venice California 04/10/98