Wednesday, January 26, 2011
According to the lab, the mirror has a P-V accuracy of nearly 1/9th wave in the wave front, and a Stehl ratio of 0.952, more than good enough for great views that are "diffraction limited." In other words, the only thing that should limit what is seen is the wave nature of light itself. Because of that, mirrors do not have to be perfect, just made well enough to offer sharp views. The glass the mirror is made of is Pyrex, a low-expansion glass that will minimize distortion due to temperature effects.
Installing the mirror was straightforward, but the design of the cell I used results in a tight fit. Some spacers will be needed to leave space for the collimation bolts to screw in or out as well, but overall the cell appears to work well. To keep curious cats out of the mirror box and off the mirror, I left the cover on it then placed a heavy battery on top of that to prevent Merlin, the youngest and most curious of them from moving it.
Now that the mirror is here, in a month or less I plan to have the telescope fully assembled, tested and in operation. The mirror will reside permanently in the mirror box to minimize the risk of breakage or other damage befalling it. I could even wash the mirror while in the mirror box, after removing all electrical and electronic components in it first. The clips have rubber bumpers and the side pins are surrounded by wooden dowels to pad the mirror from bumps and jars during handling, they will not touch it while I'm observing.
Saturday, January 22, 2011
protective wrappings and installed it in it's holder. After inserting the mirror into it's aluminum sleeve, I inserted the dew heater for it next, then polyester batting. It then took replacing the four screws to secure it to the hub and keep the very fragile, and expensive too diagonal mirror in it's cell. The mirror will now remain there until it becomes necessary to disassemble the cell again, but because the batting is not a food source for fungi and other organisms, the mirror could be washed right in it's cell without harm to it, the heater or the holder.
Tuesday, January 18, 2011
So I got out my welding machine and some 10-gauge flat mild steel stock, and spent two hours measuring, cutting, fitting and MIG welding a battery holder for a separate 18 amp-hour, 12-volt battery that will power the dew heaters and the digital setting circles independently of the cooling fan, which will draw little power on it's own even at full speed.
What emerged was a holder that will be bolted as low as possible to the front board of the rocker to prevent tippiness. A cable will then run from the battery to the Dew Buster, from which power will be fed to the dew heaters and the digital setting circles. After all the welding and clean up was completed, I sprayed it first with a metal primer, then glossy black enamel paint to prevent rusting.
Sunday, January 2, 2011
In early December the weather and the moon were favorable for a few days for observing deep sky objects. The weather the weekend after that was poor but nevertheless permitted observation of yet more galaxies and nebulae. Most of the objects I concentrated on were galaxies in the constellations Sculptor, Cetus, Pisces and Fornax, but I also looked at objects in Andromeda, Eridanus, Perseus and Cassiopeia. As before, I took my 10-inch Dobsonian to the usual landing strip to observe these objects, because none of them would have been visible from my home.
NGC 467 is one of many elliptical galaxies in Pisces that is in range of 8 and 10-inch telescopes from good sites. Resembling a distant and unresolved globular cluster or faint comet, this is a very distant galaxy that in photographs is attended by a very faint edge on spiral galaxy, which was too faint to see through my telescope that night. It's small apparent size results in a high surface brightness and therefore it's quite visible even though it's a 12th magnitude object.
The last object I sketched was NGC-1201, another Fornax galaxy that's much smaller in apparent size but much more concentrated and compact than NGC-1097. That makes it look brighter than NGC-1097 even though it's more than a magnitude dimmer, making this galaxy a good one for small telescope from more southerly regions of the world. The core is very bright and large, while the disk of the galaxy is also bright and oval in shape. A nice example of a bright galaxy that stands up well to high magnifications and doubtlessly would show a lot of detail in bigger telescopes at even higher magnification.