12-inch Ealing-Made Ritchey-Chretien Telescope for Sale


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We have a 12-inch Casssegrain optical telescope assembly for sale at an extremely attractive price: just two hundred dollars (or any reasonable offer). You pay for shipping.

The full-thickness primary mirror alone is worth much more than that as a raw piece of unfinished Pyrex! (United Lens charges $450 for an equivalent, 12.5″ diameter, roughly 2″ thick, raw, unfigured, disk of Borofloat!)

The telescope was part of a package (mount-cum-telescope) that was purchased from the Ealing company back in the 1960s by the University of Maryland. The scope itself never gave satisfactory images, so the UMd observatory sold it off in the early 1990s, and it ended up at the Hopewell Observatory about a decade before I became a member. Hopewell kept the mount, which still works quite well, but removed the telescope and replaced it with a 14-inch Celestron Schmidt-Cassegrain.

I recently examined the telescope itself (the one we are selling) and found that it indeed has a hyperbolic primary with a focal length of about 4 feet (so it’s f/4). Presumably, the convex secondary is also a matching hyperboloid, to create a Ritchey-Chretien design, but I don’t feel like perforating a large spherical mirror to create a Hindle sphere to test it properly. In any case, using a 12-inch flat, I was unable to produce decent Ronchi images.

As you may know, figuring and collimating a Richey-Chretien require a LOT of patience, more than I have. My suggestion would be to refigure the primary into a paraboloid, procure a standard flat, elliptical diagonal, and repurpose this as a Newtonian. Refiguring this mirror a task that I don’t feel like taking on, since our observatory already has a 14″ Newtonian, a 14″ SCT, and I already have built a 12.5″ Newtonian of my own. Plus, I am finding that figuring a 16.5″ thin mirror is plenty of work already.

So, our loss could be your gain! Make an offer!

I attach a bunch of photos of the OTA from several viewpoints, including a ronchigram. The mirror has been cleaned off since these picture were made; the little electronic motor was for remote focusing of the secondary.


A Weekend at Almost Heaven


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I spent Labor Day weekend at the Almost Heaven Star Party very close to Spruce Knob, the highest ridge in West Virginia. When the skies cleared at night, the stars and Milky Way were magnificent, but that only happened about 1 night out of three. My 12.5″ home-made Dobsonian telescope performed very well; in fact, because its primary and secondary mirror are almost fully enclosed by the light shrouds and upper cage, I was able to keep observing long after all the other refractors and Schmidt-Cassegrains were closed down by the heavy dew. (To keep the dew off of my finder scope and Telrad, I used large rubber bands to wrap chemical hand warmer packs around them, and that crude and cheap arrangement worked very well!)

Here are three photos taken by me:

All but the photo with the sextant were taken by Oscar.

Cleaning Up a Century-Old Refractor


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Last week, I was helping staff and students at the University of Maryland’s Observatory to clean out a storage trailer.

We noticed a seven-foot-long, 6-inch diameter telescope that had been sitting in a corner there, unused, ever since it was donated to the National Capital Astronomers (NCA) club nearly ten years earlier by the son of the original owner, Carl Kiess,  who had worked at the Lick Observatory in California and the National Bureau of Standards in or near DC, but who had passed away nearly fifty years earlier. I figured I could put it on a motorized telescope mount at Hopewell Observatory and at a minimum test the optics to see if they were any good. The current officers and trustees of NCA all said they thought this was a good idea.

One thing that caught my eye was how filthy and flaky the coating was on the tube itself, although the lens appeared to be in good shape.


The drive, while impressive, does not have a motor, requires a pier, and is extremely heavy. I decided not to mess with the drive and to put it temporarily on our existing, venerable, sturdy, motorized, electronic drive we have at Hopewell Observatory.

So I experimented with various abrasives and solvents to clean off the nasty green coating; a fine wire wheel inserted in an electric drill did the best job. Here it is partly cleaned off:

I then used Brasso for a final polish, followed by a final cleaning with acetone, and then applied several coats of polyurethane to keep it looking shiny for a number of years. (The lenses stayed covered for all of this!) So this is how it looks now:

The next task is to make a temporary holder and then put it on the mount, and then test the optics.

Silvering Mirrors, and More, at Stellafane

For me, these were the two most significant demos at the 2019 Stellafane Convention in Springfield, Vermont:

(1) Silvering large mirrors, no vacuum needed

We had a demonstration by Peter Pekurar on how to apply a layer of Silver (metallic Ag, not aluminum) onto a telescope mirror, accurately, with a protective, non-tarnishing overcoat, that works well. I looked through such a scope; the view was quite good, and I was told that interferograms are great also.

What’s more, the process involves overcoating a mirror with spray bottles of the reagents, without any vacuum apparatus needed at all. Note: Silver coated, not aluminum coated. This is big for me because the upper limit at our club’s aluminizer is 12.5″, but some of us are working on larger mirrors than that; commercial coaters currently charge many hundreds of dollars to coat them.

You can find information on some of these materials at Angel Gilding. Peter P said he will have an article out in not too long. Here are a few photos and videos of the process:


Finished mirror; notice it’s a little blotchy




(2) Demo and links for Bath Interferometer (see http://gr5.org/bath )

How to set up and use a Bath interferometer to produce highly accurate interferograms of any mirror for many orders of magnitude less cash than a Zygo interferometer. As I wrote earlier, Alan Tarica had taken the lead on fabricating one at the CCCC – NCA ATM workshop, and we eventually got it to work, but found it rather frustrating and fiddly to use.

The presenter is a HS teacher, and it shows: he explains things very clearly! On his website ( http://gr5.org/bath ) you can get plans for 3-D printing the parts for the Bath device, if you have any access to a 3-D printer, so you can print the parts out for yourself. He also has links to vendors that are selling parts for it, such as certain small lenses, mirrors and beam splitters. He shows you where you can get them for very little money from Surplus Shed and such places. Or you can purchase his really inexpensive kits that he’s already 3-D printed for you. Plus parts for an XYZ stage, which you will need for fine focus. The whole setup (not counting mirror stand and two tripods, which he assumes you have access to already) is under $130.

I will need to look carefully at our setup as built almost completely by Alan, and see how it differs and what we would need to do to make it better. The problem is that there are lots of little, tiny parts, and many of them need to be adjustable. We saw him doing LOTS of little adjustments!

Before his talk, I had absolutely no idea how this (or similar interformeters) really worked. Now I understand: the interference fringes that we see are really contour lines – like we see on on a USGS topo map, only with the mirror tilted in one direction or the other. A big difference with the USGS topo map is that there, the contour lines (isohypses – a new word for me today) are often 10 feet to 100 meters apart. In interferometry, the contour intervals are either one or one-half lambda (wavelength of light) apart – a really tiny amount! We need that level of accuracy because the surface we are studying is sooooooo flat that no other measuring system can work. His explanation of this whole thing now makes perfect sense to me. And the purpose of the software (free!) is to un-slant the mirror and re-draw it using the countour-line information.

Beautifully clear explanation!

Caution: a friend who works professionally in optics told me his team had made three Bath interferometers, using cheap but good quality ebay xyz stages, and found that they were just too much trouble; so they borrowed a very expensive commercial interferometer (costing many tens of kilobucks) from another department and are using that instead. I’m not selling my house to get a Zygo interferometer!!! But I will try the Bath interferometer instead.



Stellafane 2019 So Far

It’s been quite interesting up here at Stellafane. I’ve seen demos of a really nice DOuble pass autocollimation test.

A fellow whose email is Moonward had a much cuter, quieter, and lighter aluminizer / vacuum chamber than ours but only 7 years younger; obtained the same way as ours, via surplus giveaways from some agency discarding it.

He uses ferric chloride instead of HCl. He’d never heard of Alconox. Uses calcium carbonate slurry or else … I forget what; hope I wrote it down

I got to follow along with the optical judges. Those guys are really sharp on Star tests. The eight scopes entered had optics that were either very good or excellent. Contrary to what some folks have told me, the judges are not heartless. One of them, Francis O’Reilly, who is also Stellafane Vice President, and who had visited our telescope making workshop to see what we were up to there (at the Former woodshop of the Chevy Chase Community) and had some mirrors aluminized, asked me specifically to come up and see how they judge projects optically.

I am so glad that Francis did!

Too bad I didn’t get to look at cruddy mirrors as well. But no junk got submitted this year to us judges. I thought the images inside & out of focus looked very similar to what I’ve read in Souter and in Piekiel. I hope I can remember well enough what these looked like so that when I star test a poor mirror, then I can recall how they differ. This being my first time attempting to make a judgement, I put down no numbers. (They gave scores on a scale of 0.0 to 5.0 (best) on five criteria: contrast, symmetry, edge, and two more. I didn’t get to keep any of the papers.

No mirrors over 8″, and only one entry in the complex optical category – a schiefspueglet. I didn’t get the opportunity to look thru it. I spent a lot of time just waiting in line to look thru a scope, which is not exactly efficient. Plus, so did the contestants: they had to spend a lot of time waiting in the dark for us to show up. Fixable with a little better planning I think.

I’m not going to post pix because I’m out in the woods of VT; cell reception is 1/4 (low bandwidth) the nearest town, Springfield, is small, and actually produces a very small light dome. The Milky Way was great! Right overhead most of the night (I finally got a lift part way back to my tent around 2am.) but some high clouds as a part of a slow warm front did start coming in. Almost no dew; I wore shorts, sandals, T-shirt, and sometimes sweatshirt. Very comfy esp compared to New Mexico or DC.

So later with pix. This is off top of head in a quiet moment while it’s still fresh.

So all I got to look at last night was the bright Star Altair, rolling the focus inside and outside, with really short focal length eyepieces. In a grand total of six telescopes. out of ten submitted.

Looking at the rings of the Airy disks and rings around the star as you roll the focus of the eyepiece away from the perfect image point and then back inside. So, no, I didn’t get to view anything else in the Sky. I shoulda brought some binoculars; the sky was nice. But I was busy a good fraction of the time. If it were me, I would not have us go out in teams of 4-5, but maybe of two.

This sort of a test is the most objective one of the entire telescope. But it’s hard to do. The setup can take an incredibly long time, and the weather conditions have to be excellent: clear, steady skies, no or very little wind. And we had all of those conditions last night, which was very lucky. summer evenings in Vermont can be so beautiful, as I remember from my own long-ago years of school and work in New England.

It’s so sad to see all the empty factories just below downtown Springfield, in what was called Precision Valley in my time as a Dartmouth undergrad (1967-71). I joined SDS when I was there because they were the ones fighting against what we saw as the immoral and imperialist American war in Vietnam, and we were looking for allies in a general struggle for a more just and democratic socity, against exploitation, racism, unjust wars,m. But the War in Vietnam really focused our attention, especially since we were likely to be drafted to go fight in a war we considered unjust, and that we didn’t want to fight. (I certainly would have volunteered in WW2 and to defend the Union; but the US has also fought a lot of wars that were just plain wrong.)

we made some steps towards doing just that with blue-collar workers like the ones here at Jones & Lampson, Bryant Chucking Grinder; they were represented by the United Electrical Workers Union, which was NOT corrupt, and had leftists of some sort in its leadership. So when those workers went on strike, we in SDS did what we could to help, raising some money and walking on picket lines. It’s pretty cold striking in winter in Vermont!

This Stellafane organization is huge. I read that attendance is around 1,000 people, which makes it pretty crowded. Food isn’t nearly as good as AHSP; it’s all a la carte (hamburgers, cheese steaks, fries, scrambled eggs, etc) except for a lobster and steamer clam dinner ordered in advance (it was really, really good!). But it sure beats cooking and all the mess that entails. Lots and lots of people up here have made one or more scopes, or parts of one, or had a relative who did. At least a fraction of women and girls and other young people camping out and observing, but 8 of the judging staff were older white guys like me; two women.

Too bad I didn’t get to look at cruddy mirrors as well. There will be time for that later! Need to set that up in our shop. Just wish it didn’t take an hour and a half to set up, with help!

Today going to talks / demos of well-functioning bath interferometer and spray silvering!!!! Alan T took the lead in setting up a Bath interferometer at our lab, but we ended up not being really happy with it. Hopefully this demo will make sense.

I have already talked a bit with Peter Pekurar, who is going to be doing the spray-on silvering (NOT aluminizing!!!). He also says he has figured out how to prevent the silver from tarnishing! Amazing! And it’s cheap! (How cheap I’ll discover later)

He had a regular $2.99 mirror that he FRONT- silvered and put back into its frame, some time ago, as a demo. Completely untarnished. Unlike the few pieces of silver we have in our family, and which require constant polishing to keep shiny, this was shinier than the average bathroom mirror, because the light doesn’t have to pass through the glass twice. Amazing. The demo is 3-5 pm today.

I asked about how the procedure affects the figure of the mirror; he said they do interferograms AFTER the silvering, and they all pass with flying colors. Again, amazing.

I heard some criticism of Gary Seronik — the said that when he writes up telescopes in S&T, he never actually looks through them himself. He relies entirely on the builder. Seems to me that should always be required for that

Gotta go to bath! Not shower! Bath Ingram!

Commercial Sites for Astronomy Viewing Near New Mexico


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I thought I would share the URLs of a number of commercial establishments that offer astronomical viewing with very dark skies. Most of these are located in or near New Mexico.











http://www.csspdarkskyfund.org/home/stargazing_information  [Cherry Springs PA]

https://lennox-addington.on.ca/explore/dark-sky-viewing-area  [Ontario Canada]

And in Chile: http://www.haciendalosandes.com/en/astronomy.html

Source: Lynn Rice of New Mexico Skies, which now (sadly) only does remote hosting — in other words, people far away use the telescopes at NMS via fast internet connections, for a fee.

New Mexico Skies, Inc.
9 Contentment Crest #182
Mayhill NM 88339


The OTHER major problem with TFA

… as Peter Greene explains, is that it takes untrained newbies with TWO WHOLE YEARS (snicker) of classroom experience and claims that they are now ready to run an entire school system.

He explains:


Teach for America: The Other Big Problem

Posted: 03 Jun 2019 10:31 AM PDT

Teach for America’s most famously flawed premise is well known– five weeks of training makes you qualified to teach in a classroom. It’s an absurd premise that has been criticized and lampooned widely. It is followed closely in infamy by the notion that two years in a classroom are about providing the TFAer with an “experience,” or a resume-builder so they have a better shot at that law or MBA program they’re applying to. That premise has also been widely criticized.

There’s another TFA premise that is less remarked on but is perhaps, in the long run, far worse. From the TFA website:

To change our country’s education system, we need leaders challenging conventional wisdom and the status quo, working for the long term from both inside and outside the school system. Once you become an alum of TFA, you’ll bring an invaluable perspective to any career field in working to create opportunity for students and communities nationwide.

This is the other TFA premise– that two years in a classroom makes you qualified to run a school, or a school district, or a state education department. Two years in a classroom makes you qualified to be an education policy leader.

This is nuts.

First of all, two years in a classroom is nothing. For most folks it takes five to seven years to really get on your feet as a classroom teacher, to really have a solid sense of what you’re doing (and you will never, ever, reach a point at which you don’t have much more to learn about the work). The beginning two years are a challenge for anyone, and in the case of TFA, we’re talking about the first two years of a person who only prepped for the job for five weeks! So they are starting out behind the average traditional new teacher. And if they are teaching in, say, a charter where they are surrounded primarily by other newbies, or being coached and led by TFA staff who are alumni who only have two years in the classroom– well, the problems just compound. This is not the blind leading the blind– this is the blind being led down a cliffside path into the Grand Canyon by a blind guide who is riding on a disabled Roombah.

Second, I will totally give a large number of TFAers in the classroom credit for good intentions. Yes, some have joined up specifically to beef up their grad school application or give themselves an “experience,” but I believe that a significant number of TFAers entered the classroom hoping just what most traditional teachers hope– that they could do good and make a corner of the world a little better.

But what the heck has to be going on in your head if, after two years of classroom teaching, you’re thinking, “Yeah, I could totally run an entire school” or “I bet I could really fix this district if I were in charge” or “The education in this state would be so awesome if they put me in charge.” I told almost every student teacher I worked with, every first-year teacher I ever mentored, “It’s okay. If you don’t cry at some point during this year, that just means you don’t fully understand the situation.” How bad does your grasp have to be, how deep in the grip of Dunning-Kruger do you have to be, to look at your tiny little sliver of just-getting-your-feet-wet experience and think that you are ready to run the show? This is a level of delusion I find truly scary.

And yet. Part of TFA’s goal has always been to create the educational leaders who could turn the educational ship toward the course that their fully-amateur navigators had charted.

They’ve been successful. As a reminder, look at some of the alumni notables listed on TFA’s Wikipedia page:

Mike Feinberg (Houston ’92), KIPP Co-founder

Mike Johnston (Mississippi Delta ’97), Colorado state senator

Kevin Huffman (Houston ’92), Tennessee State Education Commissioner, April 2011 to January 2015

Michelle Rhee (Baltimore ’92), Former Chancellor of District of Columbia Public Schools and founder of The New Teacher Project and StudentsFirst

Alec Ross (Baltimore ’94), Senior Adviser for Innovation for Secretary of State Hillary Clinton

John C. White (2010), Louisiana state superintendent of education since 2012

But there are plenty of lower-profile TFA alums out there. For instance, go to LittleSis and look through just some of the Teach for America alumni connections (while you’re at it, look at who funds and runs TFA). There’s a director of industry learning at McKinsey, a vice-president at the Boston Foundation, a guy who worked for NYC’s ed department and now works in charter school development, the chief academic officer at National Heritage Academies, a partner at Learn Capital. TFA’s own alumni page includes folks now working with The Mind Trust, KIPP, and the Walton Family Foundation.

Or consider the TFA Capitol Hill Fellows Program, one of the TFA initiatives that was designed to make sure that TFA has a voice in federal education policy.

The numbers are– well, if we look at just, say, TFA in Memphis, we find there are 410 TFA alumni in town. 250 are in a classroom, 24 are school leaders, and 6 lead a school system. With two whole years in a classroom under their belts, they lead an entire system.

TFA’s own national alum figures show that 34% are in a classroom and 84% “work in education or in fields that impact low-income communities”  which works out to half the TFAers believing that their two years in a low-income classroom qualifies them to do education or community work.

You can drill down and find the specific pictures anywhere in the country. What started me thinking about this was Lorain, Ohio, a story I’ve been following that involves a state-appointed all-powerful CEO. This is a guy with two years in a classroom, and yet he has since that time launched a charter school and served as a consultant for a major urban district before coming to Lorain to run the whole system. And he’s hired “turnaround principals” who are also TFA products, who are taking over administration of entire buildings based on their two years as a beginning teacher in a classroom. And all of these folks don’t need anybody to tell them anything because they are education experts.

This is nuts.

TFA’s drive to plant its seeds everywhere is one persistent symptom of the early days of modern reform, back before when Reformsters figured out that badmouthing public school teachers was counterproductive. After all– if a two-year classroom veteran makes a good principal or superintendent or state commissioner, why haven’t more places reached out to recruit ten or fifteen or twenty year veterans of public school classrooms for leadership or policy positions (yes, teachers are allowed to rise to principal or superintendent positions, but the state capitol doesn’t call very often). If two years in the classroom make you an education expert, then twenty years ought to make you a genius. Except, of course…

TFA education policy leaders and administrators are an expression of that reform idea that we don’t just need a parallel system of education, but we need to reject all educational expertise that already exists. It’s not that hard– any person with an ivy league degree could figure out not only how to teach, but how to run a school, a district, or a state. TFA, the Broad Academy, other alternative systems deliberately reject the educational expertise that exists and attempt to build their alternative system from scratch, trusting that their own amateur-hour wisdom renders all that came before moot.

“You had five weeks of training, so now you’re ready to take over a classroom,” was silly.

“I put in two years in a classroom, so now I’m ready to take over the whole operation,” is a higher level of delusion, and yet these deluded soldiers continue to make inroads like weeds, coming first through concrete cracked open for them by their rich and powerful patrons, and then, once through, bringing more of their crew to join them.

A light-weight mirror cover for tight quarters

I built a Krueger & Berry style Dobsonian strut Mount telescope a few years ago around a 12.5″ full thickness mirror that I swapped for. The only problem was that even though the mirror sits in a box, said box has no bottom; hence, it’s no problem for all sorts of dust, pollen, and god bows what else to land on the mirror; obviously, the more Schmutz that gathers, harder it is to see stars, planets, galaxies and so on.

When I inspected the mirror last week before a little neighborhood star party at the home of another telescope maker who lives North of Baltimore, The mirror was so disgusting that I removed the mirror from its box and cell and washed it off carefully in a laundry tub that I first washed out. (Recipe: wash tub, wash hands, rinse both, put mirror under tap, rinse off as much as possible just with its flow, then fill tub part way with lukewarm water, add a fragrance-free detergent, swirl that around with fingers, then start running your clean, wet, slightly soapy water gently around the mirror. Use fingernails to pick off anything you feel. Respect. Turn mirror. Rinse. Repeat. Then rinse a bunch more. Remove mirror from water, put it on a soft clean towel that’s not hot fabric softener, on its edge; use a clean washcloth to pat dry if needed on the front.

It worked great.

Btw I’m willing to do this because I can recoat it whenever I want in our club’s alumunizer.

But taking it out & putting it back in is a PITA, and dangerous, to boot — good chances of dropping it coming out or going back in!

So I designed an inner mirror cover. It took a lot of iterations, using measurement, a geometry drawing program, numerous full sized models made from corrugated boxes we were going to recycle, and hot glue – just for the five or six cardboard prototypes. Then I used some thin lauan plywood and some reinforcements carved by band saw from thicker plywood, and some plastic sheet, pink duct tape, and colored thumbtacks.

Here are photos of the result;