10.         Appendix 4.  Changing Plate Scales

The NIRIM camera has two sets of optics, UNISIS and MLO, and each set has 2-3 plate scales.  Each of these plate scales requires a different array position for a proper focus; and for the MLO optics, the array position may have to be changed depending on the wavelength.  Also, each of these plate scales requires a different aperture. Note: WIYN uses the MLO optics.

1.     For any plate scale change, you must first retract the array stage fully clockwise so that the Red LED indicates that the stage is at the back limit switch.

2.     Change the re-imaging optics tubes by using the gold knob located between the stepper motors. You have to do this one by feel and it can be subtle!  Fully clockwise and counter clockwise is easy - you turn until you cannot turn any more. The “middle” plate scale is not as easy to find. Try it in both directions a few times.  See Table 1.

3.     Turn the array detector stage by turning the knob counterclockwise to the correct location.  Move forward (counterclockwise) until the green light comes on.  Then back off just until the green light turns off.

4.      Change the aperture mask by turning the silver knob located on the side of the dewar opposite of the stepper motors and nearest the side where the dewar window is located.  See Table 2 for locations.

Table 1. Re-imaging Optics

Table 2 Apertures