Wednesday, January 26, 2011

The primary mirror is here

Two days ago, the event for which I have been anticipating for nine months had finally took place, the arrival of the primary mirror. The mirror was made by Optic Wave Laboratories, an optics company in California for a cost of just over $2,200. Now that it's here, I installed it temporarily in the mirror cell so I can determine the length the truss tubes have to have. Once that is done, the mirror will be returned to it's storage box until the telescope is ready for star testing.

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.

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