Date: Fri, 7 May 1999 07:00:37 -0600 From: long@apo.nmsu.edu (Dan Long) Subject: 2.5m obslog 990506 ( MJD 51305 ) THURSDAY MAY 6, 1999 APACHE POINT OBSERVATORY SDSS 2.5m OBSERVING LOG Wow, what a night! In short, we got light down multiple guide fibers and used them to guide the telescope!!! It took a while to get going tonight. The first hurdle was that the altitude windscreen bumpers were adjusted to prevent the truss contacting the windscreen, and the tolerances were tightened such that when the windscreen centered up, the lower bumper was in contact with the PSS. I adjusted the alt lvdt to make the spacing between front and rear bumpers equal. The second problem was the lower azimuth amplifier. It would not reset to normal operation. Closer inspection revealed that the 120VAC led on the digital module was red. More looking around found that all cables but power had been disconnected from that Glentek. However, reconnecting the cables didn't solve the problem. The problem was solved by swapping the digital module for the one in the Glentek next to the desk in the lower enclosure. The original module is now sitting on the desk with a note that it isn't working. When working on the telescope during the day, we need to be more careful about leaving it in an operational state, or at least informing people why it isn't. The third gotcha was that the azimuth bumpers don't allow enough room for the telescope to move within the windscreen. The consequence of this was when the azimuth was powered up the windscreen started shoving the telescope around since it could never center up on its lvdt. Removing the azimuth bumpers solved this. I think we will need more space if we are to use these bumpers, and that az lvdt will probably have to be tweaked as well. Once the telescope was operational, we proceeded to remove the cartridge ( with French on the phone guiding us ). We removed the central pin so that we could use the hole on the boresight to place a fiber. This went fairly well, though we were a bit surprised how much force was required to get the cartridge to re-engage the kinematics. It took nearly 160 lbs of additional force, beyond the nominal 360 lb weight of the cartridge alone. Something like 80 lbs was expected from the spring loading of the slit-heads. Nothing appeared amiss when we checked it, so we went ahead with the latching. We plugged a fiber into the central pin hole, and slewed to the nominal position of field I at 187.5,0 fk5. I then went to a nearby fk5 star. It took a surprisingly small offset to center it up. Total calibration offset was ( .0017,.0009 ) where the offsets are in azimuth and elevation in degrees. We focused up, and got a value around 3925. We then plugged in the remaining guide fibers to field I and got light down nearly every fiber. Without the pin there is quite a focus shift radially as one moves outward from the center. We spent a fair amount of time attempting to find a decent focus value for the fibers away from the center. We never could seem to get nice looking images away from the center. Even homing the optics had no effect. By this time field I was getting a bit far over so we switched over to field K. Stars showed up here with out much additional tweaking. Calibration offsets were still only a few arcseconds. After tweaking position and focus, we decided fibers 8, 9, and 10 had the best looking images. The images looked better than for field I. I suspect some of the focus trouble we were having is that stars were not centered well in the fibers and the fall off and possible reflections were giving us odd looking images. Instrument block data was taken for 8, 9, and 10. The offset data follows. Star coords ( binned 2x2 ) inst offset (deg) Fiber 8 Fiber 9 Fiber 10 0, 0 174,124 185,59 247,86 .001, 0 184,119 176,54 252,75 .001, .001 186,129 182,45 261,80 Calulated Rotation Angles -19 211 -29 Offsets of holes (x,y) deg .26527,.32941 -.34660,-.82183 .24348,.66780 This was entered into the spectro instrument block, and guiding was attempted. It took me a while to remember the /defgstars qualifier to start guiding the first time. GUIDE ON /DEFGSTARS Once I did this guiding did work, and we chased field K into the west, to an elevation of 26 degrees. We successfully guided for 20 minutes. Arrone Merrelli took some of the frames and put them together on a web page. The url is http://ranger.phys.cmu.edu/users/merrelli/guider/ One thing I noticed in the TCC output was that the guiding data was exactly the same for all three guide probes, even the position. As guiding was working I suspect this is just a display issue and that it was showing the information on guide probe 8 for all three. With rapidly approaching dawn, and our field setting, we decided to close up at about 05:15. A VERY successful night, I would say! Dan P.S. The cartridge pin is on my desk, and the azimuth bumper parts are on the table in the enclosure.