Albireo Observatory

I’ve owned several Celestron SCT telescopes over the years and there are good and bad things about their design. I like the large light gathering ability and the compact design, but I’m not a fan of the focusing and associated mirror flop that comes with it. So, I decided to do a few mods to my newest one, even if it might lower the resale value.

This is a photo after the mods. Focusing is accomplished by releasing the locks on the mirror rods, focusing with the standard focuser, and then reengaging the locks. I have a moonlight focuser for the scope that does the automated fine focus.

The modifications includes built in filtered forced air cooling, an extra grab handle, and the lockable mirror support rods.

It’s looks as if Celestron had already considered adding the mirror rods since the mirror mount is already designed with two extra arms for them. The third arm is used for the focusing knob, and I installed 1/4″ rods in the other two.

The back of the scope already has rings cast in it to match the extra arms. I drilled the rod holes by turning and center-drilling a guide plug on my mini lathe, which insures the holes are centered in the ring castings. Then, after reinstalling the mirror in the casting, the plug was used to drill indents in the rod arms of the mirror mount\. This insures the rod holes in the back and rods installed in the arms are exactly aligned.

Two holes for fans, and one each for a 12VDC power input connector and power switch were added as well. The fans were mounted with air filters on the outside, which allows the filters to be changed without opening the scope. The fan speed is varied using a voltage-selectable wall wart power supply.

The holes for the two mirror rods were threaded for locking adapters. On the side of the rear casting two more holes were added opposite the fans for vent plugs, to allow air to escape from the tube. These are also filtered. If the cap on the central tube is removed air will also vent from it.

I also made a change to the way the secondary mirror is mounted, because over-tightening an adjustment screw while attempting to collimate the mirror could possibly push the mirror loose from its mount (if there’s the remotest chance of messing up, I will). And it’s easy to get confused on which of the three screws to turn (at least it is for me), so I modified it. Three studs were installed with locking nuts in the mount’s adjustment screw holes, springs were added to each stud, and the mount secured in place with three thumb-nuts. Tightening the nuts adjusts the tilt and spring compression. Short of physically removing the nuts, the mirror is firmly secured.

The adjustment screws on the front of the secondary mount. The only thing I’d still like to do is find or make some larger thumb-nuts for my big fingers.

I purchased a carbon fiber tube upgrade and flocked the interior to improve contrast. One issue I ran into with the carbon fiber tube is it’s very slightly smaller than the original metal tube. This allowed air to leak out around the tube ends while precooling the interior, instead of out the vent plugs. If air can leak out, then air probably can leak in bringing dust with it. This issue was solved by adding a half-inch wide strip of flocking around both the front and rear outside edges of the tube before inserting it into the castings.

A look at the front lens with central secondary mirror and the movable primary mirror at the rear. With the flocking installed, I had to shine a flashlight inside to get enough light for a decent photo.

A side view of the carbon Fiber tube. The light reflections make it hard to get a good photo. Also you can see the extra grab handle installed on the mounting plate. I wanted to add grab handles on both sides of the scope, but the castings of this “newer” model C-11 are thinner than the older one I used to own, and I just don’t trust them to be strong enough for the extra stress of handles.