The Telrad finder is one of the most useful telescope accessories ever invented. A set of glowing red rings showing you, at a glance, exactly where your telescope is pointed in the sky. I have one on each of my telescopes. The Mauna Kea VIS also equips each telescope with one of these simple devices.
They do not work so well after hitting the ground a few times.
As I have mentioned in the past, the equipment at the Mauna Kea VIS gets used hard. It is setup every single night of the year. Thousands upon thousands of people use these telescopes to see the wonders of the night sky, the first time for many. The wear and accidental damage in the darkness takes a toll.
When Deb and I were last at the VIS we spent the day cleaning eyepieces and making other repairs to the ‘scopes. One of the things I found in the storeroom was a small pile of broken Telrads. Some were missing windows, many had broken battery holders, mirrors were missing and reticle holders hanging loose. Many had been patched back together with tape or hot glue, attempts to keep them working for another night.
Quite a few had reticles that were missing or melted by exposure to sunlight. The lens that focuses the reticle’s ring pattern, projecting it into the sky, will also focus sunlight on the reticle, quickly melting the thin film if a Telrad is left in the sun.
Gathering up partial and scattered parts I collected a box of finders that I can work on later. It made quite a pathetic sight, a box of broken Telrads. A couple evenings later, five of the Telrads are now rebuilt and ready to return to duty. Four more are awaiting replacement reticles before I can call them completed. I will take them back up next time we are on the mountain, but I expect we will find something else that needs to be fixed.