Paramount ME Impressions

May 31, 2002
Updated: 11/08/2004
 
 
 

I received my Paramount ME on May 13, 2002. First light was May 16, 2002. As I go through the setup, I’ll document my findings and thoughts here. I’ll update this page periodically.

Installation

The ME arrived in three boxes, the heaviest being 75 lbs. Unpacking is definitely a two-person job, unless your back is in excellent shape. We got it up into the observatory and on the pedestal and started mounting the equipment. The cabling has to be installed first, so I routed a USB cable through the mount. I carefully unsoldered three wires at the STV head, because the DB-15 connector could not fit through the DEC shaft, and threaded that cable through. I resoldered the wires into the head afterwards. Bob Low has written up the procedure on his web site.  The Versa-plate is aptly named. You can do virtually anything with it. I decided to mount it in the forward position with the FSQ-106 on top of the RC. This was a better balance point than centering the Versa-plate on the mount. Everything went together like a dream, the fit and finish being very well done. Even the latitude scale that is machined into the two side plates was within 0.5° for my location.

 

Scopes and cabling installed. Note no external cables between scope and mount.
 

        

Scope Cabling                                                       Mount Cabling

A pair of balance knobs remove the worm from the spur gear for both DEC and RA. See the illustration below on the right for a view of the RA balance know. Turning these knobs CW fully disengages the worm gear for easy balancing. CCW re-engages it. The scope is balanced with the worms disengaged. I noted the weight balance points for booth imaging and visual work. In my case, moving the FSQ-106 forward and back is used to balance the DEC axis and the counterweights are used for the RA shaft. I marked these points with white foam Velcro loop material. If you look at the first picture, you can see the two pieces on the FSQ-106 mounting plate and one on the counterweight shaft. What was interesting to note was, after balancing, the scope could be pointed anywhere and hold its balance. This is due to not only the smooth bearings of the mount but also the through-the-mount cabling that eliminates any differential loading of balance. I suspect this wouldn’t amount to a hill of beans in overall performance, but it was nice to be able to have it almost perfect.
 

Polar Alignment

Since the ME has absolute encoders, it knows where it is within 10 arc-minutes or so. I followed the instructions in the manual, using Tpoint and the outstanding adjusters that are part of the ME.
 

Some comments are appropriate on the adjusters. I believe this is a very significant improvement in enabling precise alignment. Each adjuster knob has a rounded point, called a “tic” in the manual, that indicates in 2 arc-minute movement of both AZ and EL. The EL adjuster uses a nice jack arrangement that can be augmented by some ¼ x 20 screws to give leverage for adjusting, as shown here. The AZ adjusters use push-pull screws. The innovation here is having a bearing for the azimuth axis. It is very smooth and allows very precise adjustment. I used an Allen wrench as a reference point for adjustment, as illustrated below.

Azimuth adjuster and reference tool

Elevation adjuster and reference tool

 

The Heart of the Polar Alignment System

 

After mounting, four polar alignment runs were made, homing in on the optimized adjustments.  The results of Tpoint runs were as follows:

 

 

Azimuth adjustment needed

Elevation adjustment needed 
 

Run 1 (32 points)

Move west 4.5 arc-min.

Raise 2.2 arc-minutes

Run 2 (25 points)

Move west 1.6 arc-min.

Raise 1 arc-minute

Run 3 (29 points)

Move west 11 arc-sec. (!)

Lower 72 arc-sec.

Run 4 (78 points)

Move west 48 arc-sec.

Lower 63 arc-sec.

 

Image link and the automap script were used for all mapping point acquisition.
 
After run 1, I tried to estimate the amount of knob movement for the required adjustment. After run 2, I used the Allen wrench reference and got pretty close, run 3 indicated. After run 2, I targeted the refracted pole, which should be 80 arc-sec. above the celestial pole for my latitude and elevation. Here is a reference from Patrick Wallace that tabulates the refracted pole. Runs 1-3 were all done using targets on the east side of the meridian. No adjustments were performed between run 3 and 4, except that run 4 used both sides of the meridian. This indicates the need for the whole sky for the final adjustment.
 
Note that no drift alignment was used to get to this polar alignment. It was all done through Tpoint and automap, most of which was unattended. I subsequently ran a track.log in Maxim to assess the agreement with the Tpoint reported result.  I chose a star near the meridian at 0° declination. After 11 minutes of recording one-second exposures, I computed the slope of the drift to be 0.238 arc-sec./minute. This calculates to a polar alignment error of 54 arc-sec., which is excellent agreement with the Tpoint results. I plan to try to half the azimuth error by a small movement of the azimuth adjuster.
 
I tried moving the azimuth ever so slightly and reran a Tpoint model. The azimuth error reported by Tpoint was 21 arc-sec. The pointing accuracy was reported as 11.9 arc-sec. rms.
 
After a Tpoint run consisting of 110 points from 25° to 85° elevation, I achieved the following results:

 

 

The automap run took around 2 hours to complete with around 10 minutes of active work on my part The model includes a TX term of 79.69, which indicates some level of tube flexure that needs investigating.

OTA adjustment and results

As a result of the above data, especially the TX term, I disassembled my OTA and tightened the primary mirror mounting. After collimating, I ran a 117-point Tpoint model. The TX term reduced to 48, giving confirmation of the mirror problem and improvement. Tpoint, in addition to improving pointing and tracking accuracy, is also an excellent diagnostic tool. Here are the results after OTA rework and a slight adjustment to the polar alignment to come closer to the refracted pole.

 

 

 

This level of investigation and analysis, while time consuming, is possible only with a mount as repeatable as the ME.

 

Operation

Initial power up of the mount requires homing first. This is how the scope locates its “starting position” and, once local sidereal time is calculated, derives its pointing accuracy from that reference. When homing is successfully completed, there are two series of three beeps, each of different pitches, as first one axis then the other finds its home position. During normal tracking, the scope emits various soft “murmurs” that is referred to in the manual as the “heartbeat of the mount”. This is an apt description and the sound is somewhat reassuring that all is working properly.

The joystick is handy to move the scope around locally and the built-in LED flashlight is a nice detail.

The ME comes with updates to TheSky and Tpoint that I installed. Due to my roll-off roof, and the recommendation that the park position be close to the home position, I set the park position with the scope on the east side of the mount pointing due south.