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I decided to try to use the ASGT for autoguided long exposure photography. To do so, I needed to add a guide scope, and I just happened to have a short tube 70mm spotting scope that I got for free. The spotter scope has three tripod mount holes on the mounting block, so I needed a way to attach it to the C8. I decided to build a mounting rail out of aluminum “L” shaped stock. A three foot section is about $4 at Home Depot, plus a couple M6 machine screws, nuts, and the tripod mount screws all added up to just under $6.
I measured the length of the mounting bar and cut the proper length out. I also cut a smaller horizontal bar for the rear cell mounting points since on these C8’s, the front and rear mounting holes are not in a straight line. You end up having once screw mount on the front and two at the rear of the scope.
I used a tiny bit of “JB Weld” quick setting epoxy to mate the guide scope mounting bar and the rear cell mounting plate (see photo). After that, I marked and drilled the location of the holes required to mount it to the C8.
For the guide scope, I cut two short lengths of the “L” stock, and drilled mounting holes to attach the guide scope. After mounting the guide scope, I drilled holes on the sides where it will mount to the mounting rail, sliding over the rail. I then drilled holes in both the guide scope mounting plate, and the rail. I used a simple repeating pattern so I could adjust where the guide scope mounts. I filed the edges round so that there weren’t any sharp edges to catch on in the dark.
Quick and easy design, this took about 30 minutes to build and seems to be plenty sturdy for my light weight 70mm spotter scope.
With the ASGT mounts motor controller broken, I began researching replacement options. I ran across AstroEQ (link) which is a nice and affordable telescope interface to drive small stepper motors. I will elect to replace the ASGT motor electronics, but keep this in mind for any future EQ mount upgrades.
With over one year into using this rig (new to me in 6/2014), I figure it is time to give some details about the C11 used here at Desert Stars Observatory. It is a fairly rare Celestron C11 featuring the Ahead of its time Compustar GOTO system. This was the first system of its kind for small telescopes, really defined the direction all of them would go in years to come. There is very little documentation about the Compustars, and experts say the C11 was the least made of the three flavors, C8, C11, and C14. There are no records available for serial number/build sequence that I know of, but I do know they were all hand built as Celestron shipped them to a 3rd party to be converted to Compustars. Mine is likely to be #4 of ether all C11’s built or #4 of the Compustar line as the Forks, motors and different parts have a matching #4 on them. RA Motor with #4 and an alignment mark:
The Compustar has the coolest computer system made for telescopes! It is unfortunate that modern versions don’t offer this kind of functionality.
Compustar control box
This, like several other early GOTO telescopes were hit with the “Y2K” bug. Its computer was only programmed to handle 2 digit dates… a common practice in the 1980’s when memory was expensive. Every character that could be saved usually was. I ran it with the Y2K bug by just entering the 1995 date and time, and everything was fairly close. One other thing is that the database of positions was based on 1950 data, since 2000 had yet to come. This year I updated the brains of the control system with a Y2K update chip. This not only fixed the Y2K bug allowing dates well into the 2100’s, but also updated the star database from 1950 to year 2000 data.
Opening up the control box showed that it had a birthday just the day before I did the upgrade! The CNGC catalog EPROMS have a hand written date of 10/31/1987. I was doing the upgrade 11/1/2015!
Born on 10/31/1987
It is also a very fast and quiet GOTO system. It has a high tech whine when slewing, unlike the coffee grinder noise that the LX200 and ASGT have. Unfortunately the speed does effect GOTO positioning occasionally. It goes full speed until target, which most of the time is still near the center of FOV, but occasionally it overshoots and the target is on the edge or slightly off. Tracking is accurate, but I am currently trying to resolve a harmonic vibration when tracking at sidereal speeds. It is keeping me from having perfect round stars on exposures over 90 seconds. The tracking over time is spot on, the target will stay centered all night. But there is a very tiny 5 second oscillation noticed at very high magnifications.
C8 looks and feels TINY next to the massive displacement of the C11. The wedge for the C11 is bigger/heavier than the whole C8 setup!
C11 top – C8 bottom
Even the 90 degree diagonals are huge on the C11 compared to the C8 of the same era! I think the C11 cast diagonal may actually weigh more than the OTA of the C8.. It is a serious piece of metal and glass.
Standard C8 on left, C11 on right,
Some other bits about the C11 as I have taken it apart for service and inspection:
7″ RA Gear:
Compustar C11 Dec stepper motorC11 RAPCB is copyright 1985…
I remember getting home… could not wait to see “first light” with it. A quick look said it was amazingly sharp even though it had been sitting for years, and traveled 1000’s miles before it reached my driveway.
