The telescope is a 24" (61cm) Boller and Chivens reflector, serial number 3480. It was delivered in early 1967. It is an equatorial mount, with the RA counterweights in the base and the declination counterweights attached to the rear of the tube. Manual from similar University of Rochester telescope. The original manual furnished with the NMSU telescope has been additionally scanned as a PDF. The telescope is designed to switch between a Cassegrain secondary mirror cell system, offering f/40 and f/75 focal ratios, and a Newtonian secondary mirror cell with a f/5 focal ratio. Ever since the renovation, the Newtonian mirror cell has been installed. Note that although the focal ratio with the Newtonian cell is f/5 we have a coma corrector (2" Astrotech ATCC) mounted in front of the camera, giving an effective overall ratio of f/5.6.
Mounted on the side of the telescope is a 6" two-element refractor guide scope.
The telescope home position is currently at declination -25°, and 2 hour east of directly south. Telescope communication and control is via a Sidereal Technology Servo Controller II.
Instrumentation is mounted at the Newtonian focus at the front of the telescope.
The focuser is an Optec TCF-S.
Filters and filter wheel
50mm round filters purchased from Custom Scientific fall 2020: SDSS ugriz, BVR (old style), Halpha filter. Diffusers D25 and D38 purchased from VIAVI (RPC photonics) spring 2021.
Filter wheel is a Finger Lakes Instrumentation Centerline CL-1-14, purchased through Starizona summer/fall 2021. FLI software and Centerline software installed from FLI web site. This is a two-wheel filter wheel, with 7 slots (0-6) in each wheel. Installed ugriz, Halpha in slots 1-6 wheel0, BVR, D25, D38 in slots 1-5 wheel. After installation of filters, need to run FLIFilter.exe (seems different from FLIFilter App!) and Home filter wheel. ASCOM driver loaded from FLI (in Kepler ASCOM download). Not clear if indexing can be redone using FLIFilter.exe (see configuration window from menu). Default ordering is /0, /1, etc. for wheel0/wheel1. Filter positioning is only done in one direction, so fastest filter moves are from 0654321 in wheel 0, and from 0123456 in wheel 1 (I think).
Only define useful combinations in MaxIM DL to keep menu from being too long (49 combinations).
QHY 600 installed in spring 2021, purchased from OPT (along with a QHY CFW-3 filter wheel). This is a CMOS camera that uses a Sony IMX 455 sensor, with 9576 x 6388 3.76 micron pixels. QHY software allows for 1x1 and 2x2 binning. Given the small pixels, the latter is used.
Camera needs to have a coma corrector, currently AstroTech Coma Corrector, in front of it, which pushes focus back. This results in an effective focal ratio of f/5.6 (f/5 without). This is designed so that the last optical element should be ~75mm from focal plane; currently is much closer (~40mm?).
Previous camera was a QSI 583 science camera, connected with a Type A USB cable. The science CCD is usually set to a temperature of -20° C, but on very hot nights may not reach that temperature. Typical field of view is 18.4x13.8 arcminutes, with an unbinned plate scale of ~0.33"/pixel and an array size of 3326x2504 px. Available filters are B,V,R,I, and clear. Typical read noise is ~8 electrons. QSI583 has 5-slot filter wheel, offering B,V,R,I, and clear filters.
The guide camera is a Starlight Xpress "Lodestar" autoguider, installed in the integrated port on the science camera. The guide camera points 17' south of the center of the science field. Guider has a plate scale of ~0.5"/pixel and a field of view of 6.14x4.85 arcminutes, with a pixel array size of 752x580 pixels. The guider is uncooled. ACP Scheduler does not attempt autoguiding for exposures shorter than 250 seconds. The guide camera requires several small spacers to make it parfocal with science camera, and is connected with a mini-USB cable.
MaximDL: QSI Universal, SX Universal drivers.
Because of concerns of too much back focal distance with FLI centerline and offset guider, guider moved to 6" finder scope spring 2021. Use Starlight Xpress, purchased Starlight Xpress Ultrastar Pro from Starizona summer/fall 2021, installed 10/21.
The dome is made of white fiberglass. The dome slit home position is east, facing the Organ Mountains, and the park position is slightly left of this.( "homing" the dome basically tells it where it is; parking is just "here's where I want to leave it".) The dome drive motor (Dayton DC Gearmotor SLAF6, 12V, 12.6A) is located on the northern side of the room, and is fitted with a 10x3" drive wheel with 1" central bore and a key slot. A spring provides adjustable tension to hold the drive wheel against the dome. Dome slit manual controls are located to the right of the slit motor, and forward/reverse rotation controls are located directly under the dome motor.
Dome shutter power is provided by a 15W/1A amorphous solar panel (NPower 15W Solar 12V Battery Charger) on the exterior of the dome, approximately 90° to the right of the slit. This solar panel is protected with 1/4" plexiglass and a styrofoam shock absorber. There are two spare solar panels in the building. Power is routed through a charge controller (7A max) to a 12V battery mounted to the interior of the dome; if replacing this, make sure that the wires are secured such that they will not catch on anything during dome rotation. In case of emergency, a 12V battery trickle charger is stored in the computer room.
The dome communicates with the other electronics via a magnetic induction loop. This is the thin wire on dowels on the ledge running around the bottom of the dome interior. Be careful around the wire, as it could break easily. Automation is provided by a Diffraction Limited Maxdome II dome controller. The two Maxdome circuit boards are encased in metal boxes, one next to the manual rotation controls and one inside the manual slit control box. These circuit boards have status LEDs, visible through small holes in the boxes; this can be useful for troubleshooting. See below for more details on these cards
The dome rests on 13 4"x1.5" rolling bearing phenolic caster wheels with a 1 5/8" hub length and 3/8" bore. The axles are 2.5" long hex bolts (3/8" diam, about half an inch of thread.) There is an approximately 5" clearance between the bottom of the dome and the ledge; a typical emergency tire-replacement jack is sufficient to raise the dome enough for wheel replacement. There are also several identical horizontal wheels, which are not load bearing.
Dome is controlled by ACP; don't connect to the dome in MaximDL. Note that the dome is set up such that it will automatically close if it does not detect a signal from the control computer; so if you're up there doing maintenance and open it to let some light in, make sure the computer is on so it doesn't close itself.
After suffering a failure of the dome control card we ordered a new card from Diffraction Limited. Upon installing it the dome immediately started to rotate endlessly. Pressing the stop button did stop the rotation, but only for as long as it was held in. Upon releasing the button, the dome began to rotate again. After some posts to the support forum, and some tests, we eventually figured out what was going on. Our old cards are Revision D. The new card is Revision F. Between those two revision, Diffraction Limited changed how the cards work.
In Revision D, the motor+ and motor- terminals are held at +12V (so effectively 0V across them). When a rotation is commanded, one of the terminals drops to 0V, giving you a difference of 12V across the two terminals and engaging the motor. In Revision F they decided that holding the motor terminals at 12V is bad, just incase there’s a short somewhere. So now the terminals stay at 0V, and when a move is commanded the relevant terminal jumps to 12V. If you simply have a motor connected across the terminals then there’s effectively no difference. In revision D you have a difference of 0V until you command a move, at which point one of the terminals drops to 0 and you get you 12V difference. In Revision F they two are at 0 until a move is commanded, at which point one jumps to 12V.
However. We use a large motor to drive our large dome, so we don’t/can’t drive the motor directly from the card. We instead use the voltage from the card to trigger our large external relays, which then engage the motor. And this was wired up in such a way to expect 12V on the motor terminals, with 0v commanding a move. This was accomplished by a jumper on one of the connection block connections (on the back left of the rotation box), between the 12V connection and the relay connection. Removing this jumper set the relays back to 0V and has them trigger when the MaxDome card motor terminals are at 12V (i.e. the new card behaviour). It’s important to be aware of this behaviour for the future. We returned our faulty card to be repaired, and so now have a spare Revision D card (in the computer room downstairs). We’ll have to be careful about the wiring if we use it to replace a card in the future. The dome shutter is still wired up to use a Revision D card, the rotation box is wired for Revision F.
Weather sensing is provided by a Boltwood CloudSensor II. This will provide information regarding wind speed, humidity, cloud cover, temperature, rain, and dew point. If the weather is deemed unsafe, ACP Scheduler will not operate the observatory- it waits for at least ten minutes of continuous "safe" weather before attempting to observe. Note that the automatic weather script will trigger for unsafe weather even if you are observing manually. Nevertheless, you should probably not run Scheduler if it is likely to rain or the conditions look bad.
Power to the hardware, dome, and telescope are controlled through two internet-connected power strips. TMOPower1 is located next to the desk (western side of room). Most of the power sockets on the strips are labeled in the power control interfaces. Socket 1 controls the telescope power; note that turning this off will turn off power to TMOPower2 and all of its sockets! Socket 2 should never be left powered on!
TMOPower2 is physically mounted on the telescope itself, and controls power to the instrumentation and associated hardware. Note that this powerswitch is itself powered through the telescope power, so will only be reachable if the telescope power is on on TMOPower1.
Internet access is through a small wireless antenna on the southern side of the building, underneath the dome and pointed at the nearby radio tower. There have been instances where this antenna was vandalized or wind knocked it down; if this happens you may have little to no internet connectivity, which is bad.
The observatory does not have running water, so if you are going up to clean (or you want drinking water) you need to bring your own supply.
In the dome room itself, the desk on the western side of the room has a laptop in the bottom drawer, which is useful if you need to control the observatory while you are there. The northern side of the room has a door leading to the exterior walkway to the roof- be aware that the wooden walkway is not in good condition, so be careful when walking on it. This room also contains a tool chest and a cabinet with various parts, including spare telescope counterweights. The orange cart is a hydraulic platform which can be raised via the foot pedal, and provides an alternative to a ladder.
Horizon limiter: If the telescope gets too close to the horizon, the motor will shut off. It shouldn't be triggered in normal operation, as ACP Scheduler won't observe anything beneath 20° of the horizon. If it is, however, it requires a manual override to bring back; contact David or Jon about this.