From: Hal Petrie Date: June 8, 2006 3:31:45 PM PDT To: Antonin Bouchez Cc: Hal Petrie , Richard Dekany , Bob Thicksten , Andrew Pickles Subject: LLT for June 12 Run Antonin, We (Thicksten and I) reassembled the LLT on June 6. Changes include: 1. Shims in all truss shoulder bolts to tighten joints. Truss is still softest in torsion, but stiffer than before. 2. Changed 10" primary radial restraints and definition from felt pads to nylon screws. This is stiffer and allows easy centration of the primary. Lateral stiffness of primary restraints much higher than before. 3. Installed reworked Secondary system, including tightened linear stage and modified tilt adjustment that eliminates lateral shifts during tilt adjustment and makes definition positive. 4. Cleaned Relay Lens. As before, errant laser beams have melted the plastic retaining ring and caused smokey deposits on the lens. 5. Recollimated Primary-Secondary system for centration on the optical axis and tilt of Secondary and Primary. This was done using the laser collimator. We no longer observed Secondary translation when doing tilt adjustments. 6. Mounted the laser collimator on the Top Fold Mirror and directed it through the system. Qualitative checks make by pusing with hand on various components. Truss is stiff laterally but still has some torsional softness. Primary and Secondary stiffer to lateral loads than before. 7. As expected, small boresight changes (tilting the LLT with respect to its mounting pedestal) cause shifts in the projected laser spot on the LLT Primary. This will also change Pulnix Alignment in the Star Viewing Mode. This occurs because the FSM and Relay lens and Final Fold Mirror are on the fixed pedestal and the Top Fold Mirror and Primary and Secondary are on the tiltable LLT. 8. The mounting plate for the Final Fold Mirror was drilled and tapped for the addition of the waveplate mount for polarization control. The waveplate can be mounted in the LLT while it is on its handling cart, but not when it is mounted in Prime Focus (or at least it would be verrrry difficult in Prime Focus). If the waveplate is calibrated before Monday, I can install it Monday morning. 9. The extension piece for the Q3 quad cell did not fit because the 1/4 inch plate it adapts to on the LLT was actually .258 inch thick. The part is being reworked in the Physics Shop and I will take it to Palomar Monday morning. This piece is necessary to eliminate the problem of the Pulnix interfering with the filter in front of Q3. The new 610 nm filter should be installed at this time. 10. I reinstalled the Zaber actuator for secondary focus and noticed that the strain reliefs had pulled out on the cables. Other Zabers show the same problem. I pushed the jackets back into the housing. WE NEED TO MAKE SURE THE ZABER IS STILL WORKING AND WE WILL HAVE TO REESTABLISH THE FOCUS RANGE. Because of the extensive disassembly and rework of the LLT, we will have to go through some on-sky collimation again. I would suggest the following sequence: 1. Once the LLT is in Prime Focus, use the 660 nm laser to align the LLT to the laser. This involves the reticle in the center of the primary and the mask/target on the secondary. The FSM should be powered up for this test. The goal here is to get the laser on the center of the Top Fold Mirror, the center of the FSM, the center of the Relay Lens, the center of the primary, and the center of the secondary. I SUGGEST WE DO THIS AS SOON AS POSSIBLE DURING THE DAY. 2. Align the Pulnix in Star Viewing Mode to the LLT. Dekany and I found last time that using a bright flashlight in Prime Focus allows us to see the primary reticle and secondary target simultaneously and to quickly adjust the Pulnix until those two fiducials are coincident. 3. After either 1. or 2. above, see if we can get the Iris better centered on the laser beam (reticle/target seen in the Pulnix). I suggest this be done by physically moving the Iris in its slotted mounting hole and/or using shims. 4. Get the LLT boresighted to the 200". The moon does not rise until 9:32, so we will have to use a planet or bright star. I suspect Saturn will be too far west this month and Jupiter too far east in the early evening. If we do not find the object in the wide field mode of the Pulnix, we should try the technique we used last time of one person standing up and looking at the sky in the LLT primary and having the other person in Prime Focus use the tilt screws to move the object behind the secondary. At this point, the object can usually be found in the Pulnix. BECAUSE OF THE CHANGES TO THE SECONDARY SYSTEM WE MAY HAVE TO SEARCH FOR BEST FOCUS. I think it will be close to the values from the previous run, but could be off by as much as a millimeter. 5. Once we have the LLT aligned to the 200", try moving off the object and coming back to it. Also try going to another object and see if it comes into the field of view. If pointing is OK, go to the next step. 6. Check image quality. If it is different from AO or DIMM seeing, or if the images in narrow field mode show obvious flaring, we should probably go through the secondary translation and tilt parameter space as we did last time. 7. After collimation, check that the Pulnix is on axis. Adjust as necessary and iterate on Boresighting. 8. Once the LLT is boresighted and the Pulnix is on-axis, check the path of the red laser again and adjust as necessary. Without these last iterative steps, we may well find the Sodium Laser spot outside our field of view. The small changes for laser alignment may well put the Pulnix off-axis again, but at this point we should not be needing it any more in star viewing mode. The above procedure seems lengthy and, unfortunately, is retracing ground from previous runs. But, until the LLT design is stable optically and mechanically, I think we are best off being patient and getting it right during the first part of the first evening of the run. Part of the problem is inherent in the design where some parts move during boresighting and others do not. I remain optimistic that eventually we will be able to bolt in the LLT and have it work. During the Sodium Laser tests, I want to suggest that any changes to the waveplate rotation be done with the laser shuttered. The little holes burnt into the plastic retaining ring for the relay lens make me very cautious about sticking my hand inside the base of the LLT when the laser is on. D D D D D D D D D holes in the plastic retaining ring for the relay lens