Friday, December 24, 2010
I just got an e-mail from the optician today stating the mirror has been finished. All that remains is to add a coating of aluminum then a protective overcoat on top of that. Sometime after New Year's the mirror will arrive here, and that will allow me to complete the final steps on the telescope's construction. That will be first and foremost determing how long the truss poles have to be, and at what angle the pole blocks will have to be set. To do that, I will temporarily install the primary mirror and use a star to find out how far apart the mirrox box and the upper cage have to be. Once that is determined, I can drill the holes and bolt them permanently to the mirror box after returning the primary mirror to it's storage box. I will have to shim the bottoms of the blocks out, and likely shim the pole seats on the upper cage so the poles will slip into them easily before I tighten the wedges to secure the upper cage in place. I will cut the poles two inches too long to give me a margin for error, then I can trim them to the final length that will allow the eyepieces I now have to focus as well as leave leeway for eyepieces I will buy in the future. This way I'll avoid the risk of having to buy more aluminum tubing because I cut the truss poles too short. After these steps are done, the mirror will be pemanently installed in the mirror box and the sling attached to it with double sided tape to keep the sling from slipping off the edge of the mirror. I will then adjust the sling and side pins to support the mirror in the case of the sling, and to leave a 1/8 to 1/4-inch gap between the mirror and the side pins as well as the mirror clips. They serve to keep the mirror in place and prevent damage to it, they will not touch it normally unless the telescope is bumped or I am driving over a bumpy road. After that, I can then start making the shroud to keep out stray light, and the poles can be covered to make both holding them in the cold less rough on the hands and to supress reflections off of them. Many people use black foam pipe insulation for this, but I am going to try to use shrink wrap tubing that is normally used on large electrical cables to cover the shiny aluminum tubing. After all of these final steps are completed, at long last the telescope can be assembled, collimated then receive it's "first light" on a planet or other celestial object. The much larger aperture will make a big difference in how galaxies look, and the best time to see them is going to come soon. By the time February arrives, the M-81 group of galaxies, along with the clusters of them in Coma Berenices, Leo, Virgo, Centaurus and Hydra will be well placed for observation. There is at least 8,000 galaxies in range of a 15-inch telescope, and of those 8,000 at least 2,000 or 3,000 of them are visible in these galaxy clusters at a good site. The rest are distributed all over the sky including the apparently barren regions near the celestial poles. The massive light grasp will result in brighter examples resembling black and white photos from a dark site, with dimmer ones appearing everywhere wherever there's a galaxy cluster in our local region of the Universe.