1 Nov 2001 W. A. Traub EASY ALIGNMENT INSTRUCTIONS --------------------------- These are instructions to align the mirrors on the path from the fixed (F), delay-1 (D1), or delay-2 (D2) output beams back to the A, B, or C telescopes. Select either for "star south" or "star north" case, by turning on the switch on the wall near the VxW rack, which will move the 2 corner mirrors needed to give the appropriate case: star south star north F = A F = B D1 = B D1 = A D2 = C D2 = C Whether a star is "north" or "south" depends on its Dec and the chosen baseline. For either F, D1, or D2, place the 45-deg mirror labeled "view tel." on the appropriate point-line-plane mount on the 10-foot table, in front of the alignment telescope. Be sure it is seated properly by pushing down firmly in the center of the plate. Turn on the rotary switch labeled "45 deg exit" with the short end of the switch pointing toward the label, to put a light on the exit mirrors. Look into the telescope and focus the eyepiece so that you see the crosshairs easily. Then focus the top knob until you see the 45-deg mirror; it will appear as a vertical ellipse. Adjust the viewing mirror by hand until the telescope crosshairs are well centered on the 3 V-groove marks on the mirror (2 horizontal, one vertical); do not use the screw head as a center, since it is not the same as a V-groove. After this, do not change the viewing mirror axes, until you move to the next beam. Turn the rotary switch to "corner", and focus for greater distance (CCW) to see a square mirror, which is the SD or fixed dihedral. Technically you should command the exit mirror to make the dihedral centered, but it is probably already very close, so probably this is not needed. Turn the rotary switch to "45 deg exit" again, which lights up also the LD and fixed dihedrals. Technically you should yaw the corner dihedral to center this mirror, but that is probably already done. In practice you should now command the exit mirror to make the LD dihedral appear centered. Do this by turning on the Picomotor box, dialing up the address of the exit mirror (see map), and using the manual paddle. Be sure to turn off the Picomoter box immediately after this, as it often sends out about 1 pulse/sec to whatever motor is dialed up, and this will eventually mispoint the mirror significantly. If serious observing is to be done, you should now also repeat the last step for the LD mirror first at home and then at a large distance, say 10 m. Make sure that one setting of the exit mirror satisfies both of these cases. If not, then the corner dihedral yaw and the exit mirror need to be iterated. This is important because if you cannot see the LD mirror when it moves away from home, you will certainly vignet the beam when the LD is commanded there during a star observation. Turn the rotary switch to "corner" again, and focus on the corner target, which is a black plate of metal with a circular hole cut in it for each beam, and V-groove marks on which you can align the telescope. The beam should be centered vertically; if not, you can make a small adjustment (say 10% of the target hole diameter) of the exit mirror, but if it is a big adjustment then something is wrong and you should start again. The beam will probably not be centered horizontally, so to do this you need to run the LD yaw motor. Do this by reaching up for the small blue box; select LD1 or LD2, then with one hand on the yaw +/- switch, look at the corner target and move the yaw until it is centered horizontally. Be sure to do yaw + last, because this puts thye motor battery into a quiescent state, where it draws minimum current from the batteries; otherwise the batteries will run down in one night instead of the usual 1-2 weeks. Turn on the 12-volt power supply and focus farther to see the 4 LEDs light up at the feed mirror (the one just under the telescope). These are very bright and easy to see. Turn on the Picomotor box again and drive the corner mirror until the LEDs are perfectly aligned with your crosshairs. Go out to the telescope. Plug in all cables to the piezo control box, turn it on, and set the 2 rear switches to "null" which puts the piezo mirror into its half-way position (ie 50 volts on each axis, out of a maximum of 100 volts). Find the 4-inch diameter circular aluminum ring which fits into the 1-inch thick plate behind the primary, tape the white-painted metal circle to it (centered), and place it in the recess behind the primary and on the nominal telescope axis. Turn on the light which illuminates the target (a white line cord switch nearby). Go back to the alignment telescope and look at the outline of the piezo mirror which will appear as an 8-sided figure. Find the blue box labeled with the appropriate feed mirror and turn the knob to select that mirror. Find the X and Y motor control boxes, turn them on with the side switch, and set the motor speed knob to about the middle for medium speed. Look through the alignment telescope to see the piezo mirror, and push X or Y until the mirror appears symmetrical. You may wish to rotate the alignment telescope 45 degrees to make this visually easier. If some part of the piezo mirror seems blocked by a round edge, then the top of the stove pipe is not well centered, and you should go outside with another person and adjust the stove pipe screws at its base until the witndow at the top is well centered with respect to the shelf above it, and it will also be then out of the beam, as you can verify by going back to the alignment telescope and looking at the piezo mirror. Now look at the white target, and note that the little 1-mm hole in its center should appear to be precisely on the cross hairs. If not, try to remember where the hole is, but don't move anything just yet. Go back out to the telescope and remove the white target. Turn on the light which illuminates the secondary cover, with the black line-cord switch. For neatness, rotate the secondary cover until its inscribed cross is vertical and the letter at the top. Go back to the alignment telescope and look at the illuminated secondary cover. It should be well centered, or if not, it should be offset in the same direction as was the 1-mm hole in the whit target, but about 4-times more so. To center the secondary image, reach up and select the rotary knob labeled "piezo mirror" for this telescope. Only the Y-axis motor works on A and B. Press the y axis switch and center the secondary along this axis as best you can. If the X axis needs centering, you must go back to the telescope and move the manual screw which holds up the concrete piezo block on the south side of that block. A full turn of this screw is roughly the radius of the secondary, or a bit less. Iterate by turning this screw and going back to the alignment telescope until you get the secondary centered to well within the width of its V-groove width. Now you are done with this beam, and you may do each of the others. Turn off the lights in the hut. For best results, first turn off the telescope dome heater early in the day (unless it looks like rain). Then in mid-afternoon, open the telesocope dome by about 5 inches, and open a few window vents, to let the telescope cool, and the air temperature gradient in the shelter flatten out. A large gradient will bend the light beams, and the telescope too, of course. Then do the above alignment in the hour before or after sunset, before observing. If you are doing serious observing, the vacuum must be present at 50 torr or less before you align, or else you will be misaligned by 1-2 cm at each telescope, since the air temperature gradient in the long pipes will bend light by that much. For telescope C you must remove any bag over the feed mirror, and clear out the path in the floor of the telescope shelter so that you can see the piezo mirror. For observing the stove pipe should be in place.