Current Two-Headed Setup


The larger tube is a Celestron 14" Schmidt-Cassegrain telescope with an aftermarket carbon fiber tube made by Frank R. Uroda. Half of the original C14 aluminum tube serves as a short dew shield! Attached to it is the imaging train consiting of a Optec Pyxis rotator, SBIG AO8 fast guider, CFW10 filter wheel and ST8XME camera. The focus knob is driven by a computer controlled Robofocus motor.

The smaller upper telescope is a Celestron 11" SCT with a standard aluminum tube. The dew shield is home made from a Krazy carpet (a PVC sheet made for kids to slide down snowy hills, cost=3$!). On the back, an Optec Temperature Compensating Focuser provides motorized focus control and eliminates the image shift most SCTs suffer from. The shift is not a problem for imaging but in this case I am using a LHIRES3 spectrograph. For spectroscopy the star or object under analysis must stay on the 29m wide entrance slit. Focusing the star onto the slit with the camera behind the slit can become a chore when the target keeps disappearing. The LHIRES3 spectrograph has a reflective slit to permit the autoguider, in this an SBIG Remote Guide Head, to keep the target on the slit during the acquisition. The camera on the spectrograph, which also controls the RGH, is an SBIG ST7XME. Fortunately the gap between the OTAs is just enough to permit the ST8XME to rotate past the fixed LHIRES3.

The observatory computer is nicely tucked away in a POD bay providing lots of working room to the North of the pier.




A couple of useful formulas for calculating the power dissipation of a set of resistors. For m parallel loops of n resistors in series OR one loop of n serial groups of m parallel resistors each:
  • RT = n * R / m
  • P = 144 / RT = 144 * m / (n * R)
where R is the individual resistance of each component, RT is the total resistance and P is the dissipated power at 12V. Note that the individual resistance must be choosen to keep the power dissipated by each resistor below the rated component power. Therefore the component power rating must be less than P / (m * n).

The C14 is notorious for being a dew monster, so I installed a set resistors inside the tube near the front to provide the most efficient method of heating the Schmidt corrector plate. I used three serial sets (n=3) of three 5 ohm resistors (m=3) in parallel for a maximum power dissipation of 29W at 12V. The resistors are rated to 5W each, well above the maximum power dissipation per component of 29 / 9 = 3W. If I was going to do it over I would have choosen 3 groups of 2 parallel resistors to give me a maximum of 19W. I feel that the heaters at high power the generate tube currents which affect the image too much, and so low power operation (~6 to 10W with the Kendrick controller) with a long dew shield is a better configuration. Low power operation with a short dew shield in my climate still resulted in dewing/frosting so I switched to a standard full length (~2 feet) Celestron PVC dew shield. I have been dew/frost free so far.




Paramount MME with four 20 lbs counterweights balancing the two Schmidt-Cassegrain tubes and instrumentation. Both dovetails rails supporting the OTAs are bolted directly to the black VersaPlate. Unfortunately this arrangement has proved to be to flexible, the C14 Losmandy dovetail plate is bending in the middle causing RA guiding oscillations when the wind kicks up. I am replacing the rail with Parallax tube rings. Watch this space to see if it works! All the cables pass through the mount making unattended meridian flips less worrisome. The cable bundle includes:

The PME built-in SBIG 12V/5V cable routes power to the ST7XME on the spectrograph. The imaging ST8XME is powered through the SBIG extender. The Optec Pyxis is controlled through the built-in serial port line.




The 8" sunken floor allows me to work/view with the big telscopes at a much more comfortable height. It also puts the computer keyboard seen in the top image at a perfect height. The interlocking foam squares make a nice clean surface easy to kneel on, and have already payed for themselves many times over by cushioning the fall of expensive accessories! Highly recommended.

The plethora of AC/DC adpters, control boxes and cabling is brought under control in the small home made shelving unit on the south side of the pier. From the rats nest leaves a single 120V AC line, two USB 2.0 cables for the cameras and a single USB 1.0 cable for the Edgeport USB to x8 RS232 port module. The two 15' long USB 2.0 cables go directly from the cameras through the mount to the computer with no repeaters. In our sometimes frigid climate (-30C occasionally!), few if any USB extenders are known to work reliably.




The Paramount MME is fixed to the pier via a home made adapter plate. I originally made the concrete pier to support a Losmandy G11 and so the J-bolts protruding from the concrete are not in the correct pattern for the much larger PME. Without a large and precise vertical mill to locate the holes exactly 9.4" on center, I had to come up with an adjustable but rigid alternative. Therefore I fashioned a two part plate from 1" thick aluminum sheet. The three large clearance holes forming a triangle in the center accept the pier J-bolts. The four 1" thick spacer "blocks" allow the top of the J-bolts and locking nuts to clear under the PME and additionally give the needed adjustability for the 3/8"-24 tpi threaded holes into which the PME bolts. Each corner piece was locked to the main plate by three 1/4"-20 bolts fitted through oversized clearance holes on the bottom of the main plate into tapped holes in the blocks.