As a person who grew up in considerable envy of people who cultivated skills, I do my best as time allows to gain some. From my uncle, I got patience. From Robin Allen R.I.P., Crossbow-Maker, more patience and the appreciation of fine workmanship. Robin also taught me that NO DETAIL however small is too small to make perfect.
ATM came to me in a typical fashion as most I imagine: I wanted but could not afford a scope, so I built one.
I couldn’t finish the polishing stage, so I got help from an old hat who’s name has escaped my memory into the dark confines of history.
It had a few sleeks, the sure sign of an awkward touch during polishing but no matter. The wonders I saw through it. Of no small matter was the respect it earned me in a small town: a small teenager who built something that people couldn’t quite fathom. When that telescope made its way onto my sundeck (or a dark field) and people looked through the eyepiece, it was apparent why I built it.
Skip ahead decades, I have time, money and inclination for astronomy, and especially telescope making. I have bought a few instruments, from two small 3″ telescopes which show details of Jupiter to my 6″ and 8″ Maksutovs. Fine instruments to be sure, but the small size of the former two limits what you can see with them and the latter require me the haul out a heavy and expensive mount, putting limits on my spontenaity. I do like the new GOTO scopes but I thought it short-circuits some of the learning involved. A chance reading of a newspaper [Star-Trails] with an article on making a tile tool for grinding and bypassing the step of using an expensive and heavy glass tool caught my imagination. A second-hand 12 1/2″ Pyrex blank someone abortively started got me going. Along the way, an article about John Dobson and his mount furnished me with the other end of the problem.
A trip into someones dumpster (thank you G. Swann) for some discarded tiles (where he gave me two BOXES of 100 lbs of new ones), some grits by mail-order and some plaster was all I needed. I began on a 6″ glass tool left over and got that to a state of polish. If this is a workable mirror, only testing can answer that.
Two years of work, interrupted by sore backs, freezing cold work spaces and plain laziness has resulted in this: As of September 2010, I have a well-polished but poorly figured 12 1/2″ f/4.9 mirror, not coated. I hang around in a telescope store, looking for fuel to this folly of mine. I haven’t bought much recently, coasting on previous expenditures to allow me to stay. I came across the other mirror I need for this telescope: the diagonal. As important as the main mirror, it reflects light (and the image it carries) to where you can access it. It still had its package from its purchase back in 1987. I paid the same price as it had been bought for: $90. The name on the package caught my eye also: Lance Olkovick. I joined RASC in 2005, and paid dues starting in 2007. Lance is well-known and regarded in the ATM and astronomy community here but sadly he passed before I started going to meetings. There are some others who did this but they don’t attend any more. I want to learn this somewhat arcane skill but sadly few are available to learn from. By a strange co-incidence, the spider I bought online was made by a second local ATM of note: Gary Wolansky.
I have been indesicive with the design of the mount. I do like the Dobsonian but I also like the usability of the Porter equatorial and how it can easily be made to a tracking mount. This mirror/telescope is an experiment to some extent. Trying out ideas, seeing how and why things work the way they do.
Now, in early 2011, the mirror is much further along. It has a smooth figure that isn’t quite deep enough. Another two hours should do it. The 8″ polishing tool doesn’t have a lot of weight so it changes the figure only slowly, making it less likely to overshoot the mark. The upper cage is built now and while it is a bit rough, I think I made a good design choice by keeping the weight of it down.
This won’t be my final large telescope. I have a 18 5/8″ X 2.1″ thick Pyrex blank from EBay for “just” $425 plus shipping. A bargain. A fellow ATM did the diamond generation for me, as I want a f/4.5 or deeper mirror for this. By using a diamond tool to remove most of the glass of the curve, you get a deep, smooth depression that you can go straight to 220 grit, saving an enormous amount of effort and time.
With the advent of the Paracorr 2 for fast ratios on Newtonians, less coma will be seen and these faster mirrors are more useable. With a 9″ diameter to the outside of the light path plus 6 inches of back focus, the distance from mirror to diagonal is around 67 inches.
I still go into Van Tel to look around, slowing adding parts. I sold my `smaller`but totally excellentMN-61 (VanCam) Intes Mak-Newt 6`f6 for a 7`deluxe version with a motorized JMI focuser. It is a great optical package but I need to make the focuser work better. Needs more extension than any other of my scopes to achieve focus and somewhat slooooooow. Damn thing is bolted on to the tube, so removal is difficult. This should make getting focus with a camera possible.
I do have other ideas in the mix though.I found a SECOND identical cellular blank, ground and polished, but otherwise never mounted etc. He kept it at the pre-generated ratio of around f5, which makes it a 82` focal length, fairly high for a no-step Dobsonian. This gives me leave to be experimental with my un-ground blank, like turning it into a 16.5 inch R-C.
I don’t really wonder what happened to AMTing. Cheap scopes from China etc did most of the damage. Asking someone about the quality of these optical packages gave me a rather sour look. He pointed out that they have great coating, but are polished so hard and with little hand work they do end up being rough but since most people use low powers, they never realize it. The mirrors are also mostly BK7 optical glass or even plate glass most times for cost reasons. Since these mirrors are never fully exploited at high powers, people never bump into these shortcomings.