Friday, January 30, 2015

Astrograph Maintenance

The SHSU observatory is the proud owner of a rare gem: a Takahashi Epsilon 200 astrograph. It is a fast (f/4) Newtonian telescope with a hyperbolic primary mirror and a dedicated field-flattener lens. It was designed specifically for astroimaging. Dr. Anjal Sharma, with the help of Mike Prokosch, Brian Neitfeld, myself, and others worked to restore the telescope and its mount to operational condition and to establish procedures for producing images. Anjal documented the restoration in Resurrecting an Old Classic. The Epsilon 200 has not been manufactured for about 20 years now, and according to Anjal there are probably only about three dozen of them in existence worldwide. Maintaining and using this exciting piece of equipment has been a pleasure and a privilege, and I hope that it will be of benefit to SHSU and its students in the future.

Anjal had to focus his energies elsewhere, and so left me more-or-less in charge of the scope and its care. However,I haven't been able to make trips to the observatory as frequently as I did before my youngest was born. As a result, the Epsilon 200 has not had much use, and it has not been maintained as well as it should. It's a great scope and is capable of capturing some beautiful images, so I'm slowly trying to bring it back up to a presentable and operational state. I reread Anjal's account of the restoration and a few Takahashi manuals (for similar scopes), and decided to tackle cleaning the mirror.

The mirror was a mess. Dirt, smoke, dust, mold, spiders, various other fauna and a strange green fibrous substance have slowly built up gunk on the mirror over the years. Below is a photo of the mirror in its cell. Note the cobwebs. There were several spots of mold and something else that I can only describe as a "biological byproduct." The mirror is held in place by six clips. In addition, six small compression washers hold the sides of the mirror down inside the cell. It's in there pretty snugly.

Here is the mirror removed from the cell. Working on this telescope has made me appreciate even more the quality of workmanship that Takahashi puts into their products. This is a serious telescope that was meant to be used for serious work.

I placed the mirror into a plastic tub filled with distilled water and dish soap. Distilled water should be used because tap water and bottled drinking water contain minerals that can leave deposits. After letting it soak for an hour, I very carefully cleaned the surface with cotton balls. (The trick with the cotton balls is to move them from the inside out and to not put any pressure other than their own weight on the mirror surface.)

After three passes with the cotton balls, I rinsed the mirror with more distilled water and let it air dry. Below is the result. There are a few specs of dust that landed while it was drying, and a few spots that did not come clean. These are optically insignificant.

I also cleaned dust and cobwebs out of the tube, collimated the scope, and realigned the finders and the guide scope. Here is the reassembled scope.

I wish I had remembered to bring a DSLR, but here is a photo of some birds sitting on a power line about a quarter of a mile away, taken afocally with my phone through one of the few eye pieces that will come to focus on this scope.

I'm not an expert on telescope mirrors, but this mirror looked practically brand new after its cleaning. I'm convinced that it will continue to serve up beautiful images for many more years.

There is still more work to do:  fine-tuning the collimation, cleaning up the mount, and cleaning out the shed. In addition, I am going to write up an operations manual for students and faculty who want to use the scope for research.

A follow-up report on the astrograph:

After reassembling everything, the scope sat for quite a while before I had the chance to go out and collimate it. I struggled and fought with the adjustment screws, but could never get it quite right. This was not unusual, though, as we've never gotten the mirrors aligned properly.

We took it to Land, Sea, & Sky, Takahashi's authorized distributor in the Americas, for alignment and further cleaning. Fred Garcia, the Tak expert, reported that the primary mirror was not installed correctly! Well, color me Takahashi yellow!  I'm guessing that the mirror was misaligned even before Anjal rebuilt the scope, because he marked the mirror position before cleaning it years ago. That would explain why we've NEVER been able to get it properly aligned.

As of this update (June 2016) I haven't had time to do any imaging on the Epsilon-200 since it was fixed. However, the university has been putting it to good use observing exoplanet transits!

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