Rebuilding a Telescope
My son and I have enjoyed visiting the Duke Teaching Observatory quite a bit this past year. Through that, I learned that my friend Lisa has a very nice Dobsonian Telescope that she and her father had built. This lead me to this book which details how to build a modern Dobsonian.
Then Janell gave me a membership to TechShop for my birthday. In trying to figure out a project to tackle while using that membership I thought about building a small Dobsonian. I happened to mention this my friend Scott. Scott’s in the process of moving right now and mentioned that he had a telescope that he bought in 1977 that needed a bit of repair. After a bit, he ended up giving it to me. (Thanks Scott!). The telescope in question is a Criterion RV-6. It is a Newtonian Reflector mounted on a German Equatorial Mount with a clock drive. At some point, the telescope fell over onto the finderscope and made a hole in the tube. In addition, the primary mirror was fairly dirty with insect droppings and the focuser was pretty jammed up.
But, in general, the telescope was in good shape. TechShop RDU still hadn’t reopened yet and in investigating what it would take to restore the RV-6 I didn’t think I would need any of the specialized tools available there so I decided to go ahead and start the restoration at home. The first step was to fix the hole in the tube.
I pulled out the mirrors, took off the focuser and pulled out the tube. I was very lucky in that the tube material at the hole was still there, it was just cracked and pushed up. I pushed what I could back together and threw on a bunch of epoxy gel over the hole. After it cured, I sanded down the area and then went ahead and sanded down the entire tube. This fixed the hole.
The next problem was the primary mirror. Using instructions in the book about building Dobsonian telescopes, I cleaned the mirror. It cleaned up well, but if you look at it from the back you can see light shining through in various spots. However, since this is a 33 year old mirror, that was not unexpected. At the moment though, it is good enough for the restoration to proceed. At some point, however, I will want to send the mirrors off to be recoated.
The next part to fix is the focuser. While it was on the telescope the original focuser could be moved with a HUGE amount of effort. After taking it off, however, it is even more jammed. This wouldn’t be very conducive to using the telescope, so after reading about two separate RV-6 restorations that used a JMI RCF-Mini1 focuser as a replacement, I ordered one to replace the original focuser. It should be here sometime this week. Once it gets here I will need to make a few small modifications to the tube to make the new focuser fit (but not too much).
Once I get the focuser set up and working correctly, the telescope should work, however, the work will not be completely done. I will still need to paint the tube. The original RV-6 was painted white. While purists may not like it, I don’t believe a white telescope is a good idea. White is very reflective and when you’re trying to see faint bits of light in the sky the less reflective light you have around the better. Therefore, I plan to paint the tube blue. From a reflected light perspective, black would be better, but black would cause the tube to heat up quite a bit during the day. Blue will cause that too but not as much as black, and I like blue better than black, so there.
Once that is done, I’ll need to set up a new finderscope. I’ll have more on that later. I’ll also need to see if any repair needs to be done on the clock drive. The most common repair for the clock drive that I’ve seen is replacement of the internal cork, but thankfully that seems to be an easy enough repair.
Hopefully, I will be done with the telescope repair within the next few weeks and I can start using the telescope. I’d love to see what I need to do to start taking pictures with it.