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Category Archives: Telescope Making

Correct weight of the mystery glass

13 Wednesday Oct 2021

Posted by gfbrandenburg in Hopewell Observatorry, optical flat, Optics, Safety, Telescope Making

≈ 1 Comment

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mystery glass

More progress with the 22-inch wide, 4-inch thick mystery glass.

It took four of us old farts- Jim Kaiser, Alan Tarica, Tom Crone, and me – to extract the mirror from its case (which was located under a very heavy Draper-style grinding and polishing machine) roll it onto a little stand we fabricated on a decent gym scale I borrowed from my gym ( http://www.True180.fitness ) and weigh it.

We were very careful when moving that heavy mirror. Nobody got hurt in any way. When putting the mirror back into its sturdy wood carrying box, we used ancient Egyptian technology of little rollers, and it worked like a charm.

The bathroom scale we had used earlier, up at Hopewell was very, very wrong. We found that the weight of the glass was really 212 pounds (about 96 kilograms, or 96,000 grams), not 130 pounds. Its volume was 20,722 cc, so its density is roughly 4.6. Will have to see what types of glass have roughly that density and an index of refraction of about 1.72 to 1.76.

I heard from one veteran telescope maker:

“I’ve been in the Tucson astronomy club for many decades and also in the optics industry there. Most all institutions that had connections to astronomy or optics in the 60s got portions of several semi loads of “glass bank glass”, glasses that at one point in the past were considered strategic materials for certain optical designs/systems. There was a wide variety of materials, but almost all was identified in some way. We’re there any markings ar data scribed in the glass? The largest I saw was about 15”, so yours might be a different source.

“A co-worker of mine has identified several mystery glasses from an accurate determination of density. Seems like you should be able to get better results w/a more accurate scale. Also many glass types made decades ago are obsolete – my friend has some older glass catalogs that might help you determine what it might be with more accurate numbers.”

So these were cast-offs from the Military Industrial Complex, basically: pieces of glass that the military decided it no longer needed for projects that had either been completed or abandoned, and that they didn’t feel like storing any more. So they gave them away to groups like National Capital Astronomers and Hopewell Observatory.

The only markings on the glass are the following: a heavily inscribed (by hand) apparent date of 2-8-56, which probably means either February 8 of 1956 or the 2nd of August 1956. Judging by the handwriting style of the numerals, it was probably Feb. 8 of 1956 (US style). Under that are the numerals 0225, which we have no idea about. In pencil, someone with US-style handwriting wrote what looks like “Low #” in cursive. Again, we have no idea what that means.

Thanks so much, Jim, Alan, and Tom!

Satisfying Fixes Made to 50-year-old Electro-mechanical Telescope Drive at Hopewell Observatory

29 Wednesday Sep 2021

Posted by gfbrandenburg in astronomy, Hopewell Observatorry, Optics, Telescope Making

≈ 2 Comments

Tags

declination, Ealing mount, gear-motor, Hopewell Observatory, OnStep, Optics, right ascension, stepper motor, Telescope

About a week week ago, the right ascension (or RA) drive on a vintage mount at the Hopewell Observatory stopped working. Instead of its usual hum, it began making scraping noises, and then ground to a halt. (This drive is the one that allows one to track the stars perfectly as the earth slowly rotates.)

Another member and I carefully removed the drive mechanism, and I took it home. At first, I thought it was the motor itself, but after examining it carefully, I noticed that some clutch pads inside the gearbox had come unglued, causing the clutch plates to be cockeyed. The motor itself worked just fine when disconnected from the gear box.

I recalled that the pads and the clutch had been very problematic, and that our resident but now-deceased electro-mechanical-optical wizard Bob Bolster had had to modify the gearbox quite a bit. I carefully disassembled the gearbox and used acetone to remove all the old glue that he had used to glue the pads on. After doing some research to find some equivalent pad material, I yesterday ordered some new gasket material with adhesive backing from McMaster-Carr. Lo and behold, I received it TODAY! Wow!

I cut out new pads, re-assembled everything, and the gears and worm drive work just fine. Not only that: there were no screws or nuts left over!

In addition, I now see how we can replace the extremely complicated partially-analog clutch-and-drive mechanism, in both RA and in Declination with a much simpler stepper-motor system using something called OnStep.

Here is a photo of the some of the innards of the scope:

A bit complicated, no?

In the next photo, my pencil is pointing to the clutch pads inside the gear box that had come loose, causing the clutch plates to become cockeyed, jamming the gears. The clutch is so that the observer can ever-so-slightly tweak the telescope forward or backwards in RA, in order to center the target. There is another gearbox for the declination, but it’s still working OK, so we left it alone.

The synchronous gear-motor in the background. My pencil is pointing to the problem.

Of course, we still have to re-install the gearbox back in the scope.

Bob Bolster, mentioned above, was one of the founding members of the Hopewell Observatory. He was an absolute wizard at fixing things and keeping this telescope mount going, but he is no longer alive. I was afraid that I would not be able to fix this problem, but it looks like I’ve been successful.

I append an image of a very beautifully-refurbished Ealing telescope and mount – similar to the one owned by Hopewell – that belongs to the Austin Astronomical Society. Ours is so much more beat up than this one that it’s embarrassing! Plus, both we and the University of Maryland were unable to get the telescope itself, which is a Ritchey-Chretien design, ever to work properly. So we sold the mirror and cell to a collector in Italy for a pittance, and installed four other, smaller scopes on the mount instead.

Disturbing Racist Clauses Found in Early NCA Constitutions & Bylaws

29 Wednesday Sep 2021

Posted by gfbrandenburg in astronomy, History, science, Telescope Making

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Albert Einstein, amateur, astronomy, Black people, by-laws, Carnegie Institution of Washington, Caucasian, CIW, constitution, DC, ERO, Eugenics, Eugenics Records Office, Fairfax, George Carruthers, High Schools, History, Hitler, Montgomery County, National Capital Astronomer, Nazis, NCA, Prince George's County, Racism, science, Segregation, Star Dust, Washington

By Guy Brandenburg

Recently, while preparing to give a talk at this year’s Stellafane telescope-makers’ convention, I was disappointed to discover that the National Capital Astronomers (NCA), which I’ve belonged to for about 30 years, specifically excluded Black members for nearly 3 decades: from about 1940 all the way up to1969.

But NCA didn’t start out being overtly racist. Our original 1937 founding document has no such language. It reads, in part,

“The particular business and objects of [the NCA] shall be the education and mutual improvement of its members in the science of Astronomy and the encouragement of an interest in this science among others. (…) The activities of this Association are designed for the enjoyment and cultural profit of all interested in astronomy, whether the member be a beginner, an advanced student, or one whose pursuit of the science is necessarily desultory.”

And today’s NCA home page reads, “All are welcome to join. Everyone who looks up to the sky with wonder is an astronomer and welcomed by NCA. You do not have to own a telescope, but if you do own one that is fine, too. You do not have to be deeply knowledgeable in astronomy, but if you are knowledgeable in astronomy that is fine, too. You do not have to have a degree, but if you do that is fine, too. WE ARE THE MOST DIVERSE local ASTRONOMY CLUB anywhere. Come to our meetings and you will find this out. WE REALLY MEAN THIS!”

But in the 1940’s, the original open-minded and scientific NCA membership policy changed. The January 1946 Star Dust listed a number of changes to be voted on by the membership in the club’s founding documents. (See https://capitalastronomers.org/SD_year/1946/StarDust_1946_01.pdf ) The organization voted to change article III of its constitution as follows:

From:

“only Caucasians over 16 years old are eligible for membership.”

To this:

“to include all ages (see by-laws), exclude only the Black race.”

While it may be shocking that a scientific organization like NCA had such a policy, people often forget how racist a nation the USA used to be, and for how long. If you look up actual pages of DC area newspapers from the 1950s, you will note that the classified advertisements were largely segregated both by race and by gender – want ads would very often specify male or female, single or married, White-only or Colored-only jobs, apartments, and so on.

Schools in DC, MD, and Virginia were mostly segregated, either by law or in practice, up until the late 1960s or early 1970s. The 1954 Brown v Board decision had very little real impact in most areas until much, much later. Queens (NYC), PG County (MD) and Boston (MA) had violent movements against integrating schools in the 1970s. I know because I attended demonstrations against those racists and have some scars to prove it.

While the Federal and DC governments offices were integrated immediately after the Civil War, that changed for the worse when Woodrow Wilson was elected President in 1912.

Many scientists in the USA and in Europe believed the pseudo-scientific ideas of racial superiority and eugenics that arose around 1900 and were still widespread 50 years ago – and even today, as recent events have sadly shown.

In The War Against the Weak: Eugenics and America’s Campaign to Create a Master Race, Edwin Black explains how august scientific institutions like the Carnegie Institution of Washington (CIW), the American Natural History Museum in New York, and a number of eminent statisticians and biologists for many decades supported the Eugenics Records Office (ERO) at Cold Spring Harbor. So did the fabulously wealthy Rockefeller and Harriman Foundations.

The ERO pushed the concept of the genetic superiority of the ‘Nordic’ race and helped to pass State laws sterilizing the ‘weak’ and forbidding interracial marriage. They were also successful in passing the 1924 Federal immigration law that severely cut back immigration from parts of the world where supposedly ‘inferior’ people lived – e.g. Eastern and Southern Europe. As a result, many Jews who would have loved to escape Hitler’s ovens by crossing the Atlantic never made it.  

Hitler and his acolytes always acknowledged their ideological and procedural debt to American eugenical laws, literature, and propaganda. As we all know, Germany’s Nazis put those ideas to work murdering millions of Jews, Gypsies, Slavs and others.

It took more than three decades for the CIW to withdraw their support of the ERO. A CIW committee concluded in 1935 “that the Eugenics Record Office was a worthless endeavor from top to bottom, yielding no real data, and that eugenics itself was not a science but rather a social propaganda campaign with no discernable value to the science of either genetics or human heredity.” (Black, p. 390) The members pointedly compared the work of the ERO to the excesses of Nazi Germany. However, it took four more years for CIW to cut all their ties – shortly after Hitler invaded Poland in 1939, starting World War Two.

I don’t know exactly when the ‘Caucasian’-only policy became part of the NCA rules, but it seems to have been between the club founding in 1937, and October 1943 when volume 1, number 1 of Star Dust was printed. At one point, perhaps around 1940, NCA decided that only ‘Caucasians’ over 16 could join. But as indicated above, in 1946, the racial exclusion policy was narrowed to only exclude Black people. Apparently Jews, Italians, young people, Latin Americans, and Asians were eligible to join NCA from 1946 to 1969. But not African-Americans.

While researching my talk, I found that the NCA held amateur telescope-making classes at a number of all-white DC, MD, and VA high schools, from the 1940s through about 1970, both during the days of de jure segregation and the merely de-facto type: McKinley, Roosevelt, Central, Bladensburg, Falls Church, and McLean high schools are listed. While Star Dust mentions a telescope-making course at (the largely-Black) Howard University in 1946, there is no mention of any assistance for that course from NCA.

I also found no evidence in any issue of Star Dust from that era that anybody at the time raised any vocal objections to racial exclusion. Not in 1946, nor 23 years later when the rule prohibiting Black members was quietly dropped (in 1969) when a new constitution was adopted.

A few current or past NCA members confirmed to me that at some point, they noticed that racist language and privately wondered about it. One person told me that they definitely recalled some now-deceased NCA members who were openly racist and not shy about expressing those views. Others told me that they had never heard any discussion of the subject at all.

 (As one who grew up in DC and Montgomery County, and attended essentially-segregated public schools there, I am sorry that neither I nor my family actively spoke up at the time, even though a farm adjacent to ours in Clarksburg was owned by a Black family [with no school-age children at the time]. Amazing how blind one can be! The racists of those days were not shy about committing violence to achieve their ends. Fear might be one reason for silence.)

One possibility is that some of the early NCA meetings might have been held at private residences; perhaps some of the racist members insisted in preventing non-‘Caucasian’ or ‘Black’ people from attending. It is too bad the other NCA members didn’t take the other route and stay true to the original ideas of the club, and tell the racist members to get lost.

Very ironic: the late George Carruthers, a celebrated Naval Research Labs and NASA scientist, and an instrument-maker for numerous astronomical probes and satellites, gave a talk to the NCA in September of 1970 – not too long after the NCA apparently dropped its racist membership rules (April, 1969). So, a mere year and a half before he gave his talk, he could not have legally joined the organization. Nor could he have done so when he was making his own telescopes from scratch as a teenager in the 1940s. See https://en.wikipedia.org/wiki/George_Robert_Carruthers on the life and work of this great African-American scientist and inventor.

To NCA’s credit, we have done better in the past few decades at encouraging participation in telescope viewing parties, telescope making, and lectures by members of all races and ethnic groups. However, I often find that not very many NCA members bring telescopes to viewing events, or show up to judge science fairs, in mostly-minority neighborhoods. Often, it’s just me. That needs to change. We need to encourage an interest in science, astronomy, and the universe in children and the public no matter their skin color or national origin, and we need to combat the racist twaddle that passes for eugenics.

I anticipate that NCA will have a formal vote repudiating the club’s former unscientific and racist policies and behavior. I hope we will redouble our efforts to promote the study of astronomy to members of all ethnic groups, especially those historically under-represented in science.

We could do well to note the words that Albert Einstein wrote in 1946, after he had been living in the US for a decade, and the same year that NCA confirmed that Black people could not join:

“a somber point in the social outlook of Americans. Their sense of equality and human dignity is mainly limited to men of white skins. Even among these there are prejudices of which I as a Jew am clearly conscious; but they are unimportant in comparison with the attitude of the “Whites” toward their fellow-citizens of darker complexion, particularly toward Negroes.

The more I feel an American, the more this situation pains me. I can escape the feeling of complicity in it only by speaking out.

Many a sincere person will answer: “Our attitude towards Negroes is the result of unfavorable experiences which we have had by living side by side with Negroes in this country. They are not our equals in intelligence, sense of responsibility, reliability.”

I am firmly convinced that whoever believes this suffers from a fatal misconception. Your ancestors dragged these black people from their homes by force; and in the white man’s quest for wealth and an easy life they have been ruthlessly suppressed and exploited, degraded into slavery. The modern prejudice against Negroes is the result of the desire to maintain this unworthy condition.

The ancient Greeks also had slaves. They were not Negroes but white men who had been taken captive in war. There could be no talk of racial differences. And yet Aristotle, one of the great Greek philosophers, declared slaves inferior beings who were justly subdued and deprived of their liberty. It is clear that he was enmeshed in a traditional prejudice from which, despite his extraordinary intellect, he could not free himself.

What, however, can the man of good will do to combat this deeply rooted prejudice? He must have the courage to set an example by word and deed, and must watch lest his children become influenced by this racial bias.

I do not believe there is a way in which this deeply entrenched evil can be quickly healed. But until this goal is reached there is no greater satisfaction for a just and well-meaning person than the knowledge that he has devoted his best energies to the service of the good cause.”

Source: http://www.kganu.net/sitebuildercontent/sitebuilderfiles/alberteinsteinonthenegroquestion-1946.pdf

I am indebted to Morgan Aronson, Nancy Byrd, Richard Byrd, Geoff Chester, Jeff Guerber, Jay Miller, Jeffrey Norman, Rachel Poe, Todd Supple, Wayne Warren, Elizabeth Warner, and Harold Williams for documents, memories, and/or technical support.

First Telescope Making Class Since March of 2020!

15 Wednesday Sep 2021

Posted by gfbrandenburg in astronomy, Optics, Telescope Making

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aluminizing, Coulter, Mirror, parabolization, Silvering, spherical, Telescope

Tonight we were finally able to hold a telescope making workshop again, for the first time since March 13, 2020, according to our log-in sheet.

We had five people, and we looked at several mirrors.

The first one was a plate glass, 10″, f/5.5 Coulter mirror that Kevin Hartnett had obtained and wanted me to strip the old aluminum coating from and then silver it and overcoat it. I thought the coating looked rather good, especially given its age, and wanted to put it on the testing stand to see how the figure looked. All of us thought the geometric figure of the mirror looked pretty good, and the ronchi lines looked nice and smooth. Alin Tolea said he saw a narrow turned down edge region perhaps 1/4″. Kevin thought it performed well, and I can see why.

I hope my silvering job turns out at least as good as its current aluminization.

Here are a few frames from my video of the Ronchi images (100 lines per inch):

The second one was a 17.5″ f/4.5 pyrex mirror, also originally made by Coulter and then refigured by somebody called Optical Western Labs (?) in California. The owner, We did not like this mirror at all. We thought the Ronchi lines were not smooth; there is a raised area in the center; and it even shows some signs of astigmatism. Here are a couple of frames the video I took of its Ronchi measurements:

The third mirror was an 8″, under-f/4 plate glass mirror that the owner reported performed very poorly. Once we put it on the stand, we saw why: it had never been parabolized! The Ronchi lines were almost perfectly straight! You only want straight Ronchi lines if your goal is to have a spherical (as opposed to parabolic, ellipsoidal, or hyperbolic) mirror. That’s why all its images were blurry. Nagesh Kanvindeh immediately decided to start trying to parabolize it, and we happened to have a synthetic pitch lap of 8″ diameter that had been last used to finish an f/4 mirror, so he got started right away.

By the way, our new hours are 5:00 pm to 8:30 pm, Tuesdays and Fridays.

A piece of mystery glass

29 Sunday Aug 2021

Posted by gfbrandenburg in astronomy, Hopewell Observatorry, Math, Optics, Telescope Making

≈ 3 Comments

Tags

ATM, barium, Bausch & Lomb, Bureau of Standards, flint, glass, Hopewell Observatory, Math, mystery glass, Optics, Schott, Snell's Law, Telescope

Many years ago, the late Bob Bolster, a founding member of Hopewell Observatory and an amazing amateur telescope maker, got hold of a large piece of glass, perhaps World War Two military surplus left over from the old Bureau of Standards.

I have no idea what it is made out of. If Bob had any clue about its composition, he didn’t tell anyone.

Its diameter is 22 inches, and its thickness is about 3.25″. It has a yellowish tint, and it is very, very heavy.

If you didn’t know, telescope lenses (just like binocular or camera lenses) are made from a wide variety of ingredients, carefully selected to refract the various colors of light just so. Almost all glass contains quartz (SiO2), but they can also contain limestone (CaCO3), Boric oxide (B2O3), phosphates, fluorides, lead oxide, and even rare earth elements like lanthanum or thorium. This link will tell you more than you need to know.

If you are making lenses for a large refracting telescope, you need to have two very different types of glass, and you need to know their indices of refraction very precisely, so that you can calculate the the exact curvatures needed so that the color distortions produced by one lens will be mostly canceled out by the other piece(s) of glass. This is not simple! The largest working refractor today is the Yerkes, with a diameter of 40 inches (~1 meter). By comparison, the largest reflecting telescope made with a single piece of glass today is the Subaru on Mauna Kea, with a diameter of 8.2 meters (323 inches).

For a reflecting telescope, one generally doesn’t care very much what the exact composition of the glass might be, as long as it doesn’t expand and contract too much when the temperature rises or falls.

We weren’t quite sure what to do with this heavy disk, but we figured that before either grinding it into a mirror or selling it, we should try to figure out what type of glass it might be.

Several companies that produce optical glass publish catalogs that list all sorts of data, including density and indices of refraction and dispersion.

Some of us Hopewell members used a bathroom scale and tape measures to measure the density. We found that it weighed about 130 pounds. The diameter is 22 inches (55.9 cm) and the thickness is 3 and a quarter inches (8.26 cm). Using the formula for a cylinder, namely V = pi*r2*h, the volume is about 1235 cubic inches or 20,722 cubic centimeters. Using a bathroom scale, we got its weight to be about 130 lbs, or 59 kg (both +/- 1 or 2). It is possible that the scale got confused, since it expects two feet to be placed on it, rather than one large disk of glass.

However, if our measurements are correct, its density is about 2.91 grams per cc, or 1.68 ounces per cubic inches. (We figured that the density might be as low as 2.80 or as high as 3.00 if the scale was a bit off.)

It turns out that there are lots of different types of glass in that range.

Looking through the Schott catalog I saw the following types of glass with densities in that range, but I may have missed a few.

2.86  N-SF5

2.86 M-BAK2

2.89 N-BAF4

2.90 N-SF8

2.90 P-SF8

2.91 N-PSK3

2.92 N-SF15

2.93 P-SF69

2.94 LLF1

2.97 P-SK58A

3.00 N-KZFS5

3.01 P-SK57Q1

By comparison, some of the commonest and cheapest optical glasses are BAK-4 with density 3.05 and BK-7 with density 2.5.

Someone suggested that the glass might contain radioactive thorium. I don’t have a working Geiger counter, but used an iPhone app called GammaPix and it reported no gamma-ray radioactivity at all, and I also found that none of the glasses listed above (as manufactured today by Schott) contain any Uranium, Thorium or Lanthanum (which is used to replace thorium).

So I then rigged up a fixed laser pointer to measure its index of refraction using Snell’s Law, which says

Here is a schematic of my setup:


The fixed angle a I found to be between 50 and 51 degrees by putting my rig on a large mirror and measuring the angle of reflection with a carpentry tool.

And here is what it looked like in practice:

I slid the jig back and forth until I could make it so that the refracted laser beam just barely hit the bottom edge of the glass blank.

I marked where the laser is impinging upon the glass, and I measured the distance d from that spot to the top edge of the glass.

I divided d by the thickness of the glass, in the same units, and found the arc-tangent of that ratio; that is the measure, b, of the angle of refraction.

One generally uses 1.00 for the index of refraction of air (n1). I am calling n2 the index of refraction of the glass. I had never actually done this experiment before; I had only read about doing it.

As you might expect, with such a crude setup, I got a range of answers for the thickness of the glass, and for the distance d. Even angle a was uncertain: somewhere around 49 or 50 degrees. For the angle of refraction, I got answers somewhere between 25.7 and 26.5 degrees.

All of this gave me an index of refraction for this class as being between 1.723 and 1.760.

This gave me a list of quite a few different glasses in several catalogs (two from Schott and one from Bausch & Lomb).

Unfortunately, there is no glass with a density between 2.80 and 3.00 g/cc that has an index of refraction in that range.

None.

So, either we have a disk of unobtanium, or else we did some measurements incorrectly.

I’m guessing it’s not unobtanium.

I’m also guessing the error is probably in our weighing procedure. The bathroom scale we used is not very accurate and probably got confused because the glass doesn’t have two feet.

A suggestion was made that this might be what Bausch and Lomb called Barium Flint, but that has an index of refraction that’s too low, only 1.605.

Mystery is still unsolved.

Clay Davies’ Links for Telescope Makers

24 Thursday Dec 2020

Posted by gfbrandenburg in astronomy, flat, optical flat, Telescope Making

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Tags

albert highe, CLay Davies, Commercial, dobsonian, explore scientific, Jean Texereau, Mel Bartels, newtonian, R. F. Royce, Reiner Vogel, Royal Astronomical Society of Canada, stargazer steve, stellafane, Telescope Making, trigonometry

I am copying and pasting Clay Davies’ recent article published on a Facebook page for amateur telescope makers, where he gives links to extremely useful sources as well as commentary. I think he did a great job, and want to make this available to more people.

================================= here goes! ================================================

Amateur Telescope Making Resources & Fast Commercial Newtonian Telescopes

  • Observer’s Handbook, Royal Astronomical Society of Canada. Every amateur astronomer should have at least one copy of this book. Every “newby” should read it cover to cover. Old hands should keep it as a reference. Avid astronomers get it every year, because it’s updated annually.
  • How to Make a Telescope, Jean Texereau. A classic book by a superb optician. The author taught many people how to make their own telescopes, including grinding, polishing and figuring their own mirrors. This book offers unique and practical telescope and mount designs I have never seen anywhere else.
  • The Dobsonian Telescope, David Kriege & Richard Berry. Want to knock off an Obsession telescope? Here is your bible, written by the creators of Obsession Telescopes. Here you will find well thought out and time proven designs for truss Dobsonian telescopes from 12.5” to 25” and more. If you are handy, if you use one of these designs and follow step-by-step instructions, you can build a fine truss dobsonian. But use free PLOP software (below) to design your mirror cell.
  • PLOP Automated Mirror Cell Optimization. This free windows software can help you design a “perfect” mirror cell. Just plug in the numbers, and in seconds, you have a mirror cell design. https://www.davidlewistoronto.com/plop/
  • Engineering, Design and Construction of Portable Newtonian Telescopes, Albert Highe. Do you want your next telescope to truly satisfy you? This book dedicates an entire chapter that asks you questions that help you design and build (or buy!) a telescope that will do just that. And it has beautifully engineered contemporary designs for large truss telescopes.
  • Engineering, Design and Construction of String Telescopes, Albert Highe. Beautifully engineered, yet challenging, ultra-light, air transportable newtonian telescope designs.
  • Newt for the Web (Stellafane). This is a simple, yet effective tool for newtonian telescope design. You can design an excellent telescope with just this free tool, plus old school drafting tools like ruler, protractor, pencil and compass. https://stellafane.org/tm/newt-web/newt-web.html
  • Reflecting Telescope Optimizer Suite. Mel Bartels created this wonderful free online newtonian telescope design tool: https://www.bbastrodesigns.com/telescopeCriteriaCalc.html If you explore Mel’s website you will find innovative, ultra-fast dobsonian telescopes, beautiful deep sky sketches, and mind expanding ideas that will probably make you a better observer. https://www.bbastrodesigns.com/The%20New%20Sub-F3%20Richest%20Field%20Telescopes.html
  • Right Angled Triangles Calculator, Cleve Books. Are you building a truss telescope but can’t remember trigonometry? This site makes it easy: http://www.cleavebooks.co.uk/scol/calrtri.htm
  • Stargazer Steve 6” Truss Telescope. A very portable, ultra-light commercial truss telescope. Moderately priced, too! http://stargazer.isys.ca/6inch.html
  • Explore Scientific 8”f3.9 Want a fast scope but don’t want to build it? This fast astrograph optical tube assembly has a carbon fibre tube and weighs 18.3 pounds / 8.3kg. It’s remarkably affordable, too! https://explorescientificusa.com/products/208mm-newtonian-f-3-9-with-carbon-fiber-tube
  • Orion 8” f/3.9 You can save a lot of work by buying a telescope off the shelf, like this one. Similar to the Explore Scientific, but with a steel tube at an irresistable price. And this OTA is under 18 pounds / 8kg! https://www.telescope.com/Orion-8-f39-Newtonian-Astrograph-Reflector-Telescope/p/101450.uts
  • R. F. Royce Telescope Building Projects. Simple newtonian telescope designs by one of the finest opticians on planet Earth. The first telescope I built, a 10”f6, and the second telescope I built, a 6”f8, were both based on Royce’s designs. Both performed far beyond my expectations. In fact, the surrier-trusses for my 8”f4 design were based on the Royce design. http://www.rfroyce.com/Telescope%20Bulding%20Projects.htm Want to build your ultimate lunar and planetary telescope? Click the third link. And… considering how much you can learn from one of the world’s greatest opticians, shouldn’t you click every link? http://www.rfroyce.com/thoughts.htm
  • Reiner Vogel Travel Dobs. If you are interested in designing and building your own telescope, have a look at this website. You will find easy and effective construction techniques and ultralight, ultra-portable telescopes here. And big ones. You’ll find equatorial mounts and observing notes, too! http://www.reinervogel.net/index_e.html?/links_e.html
  • Here is my talk at the RASC, Toronto, (Royal Astronomical Society of Canada) entitled, “Designing and Building a Newtonian Telescope for Wide Field Visual and Air Travel”. You can scroll the video to 38:20 if you want to go directly to my presentation. https://www.youtube.com/watch?v=Gz7TVQkTGCM

SOLD: Antique 6″ f/14 Refractor With Good Optics Available No Longer

05 Monday Oct 2020

Posted by gfbrandenburg in astronomy, astrophysics, History, Hopewell Observatorry, Optics, Telescope Making

≈ 1 Comment

Tags

achromat, brass, Carl Kiess, doublet, John Brashear, optical tube assembly, refractor, Telescope

The Hopewell Observatory had available a finely-machined antique, brass-tube 6″ f./14 achromatic refractor.

The mount and drive were apparently made by John Brashear, but we don’t know for sure who made the tube, lens, focuser or optics.

We removed a lot of accumulated green or black grunge on the outside of the tube, but found no identifying markings of any sort anywhere, except for the degrees and such on the setting circles and some very subtle marks on the sides of the lens elements indicating the proper alignment.

The son of the original owner told me that the scope and mount were built a bit over a century ago for the American professional astronomer Carl Kiess. The latter worked mostly on stellar and solar spectra for the National Bureau of Standards, was for many years on the faculty of Georgetown University, and passed away in 1967. A few decades later, his son later donated this scope and mount to National Capital Astronomers (of DC), who were unable to use it. NCA then later sold it to us (Hopewell Observatory), who cleaned and tested it.

The attribution of the mount to Brashear was by Bart Fried of the Antique Telescope Society, who said that quite often Brashear didn’t initial or stamp his products. Looking at known examples of Brashear’s mounts, I think Fried is probably correct. Kiess’s son said he thought that the optics were made by an optician in California, but he didn’t remember any other details. His father got his PhD at UC Berkeley in 1913, and later worked at the Lick Observatory before settling in the DC area. The company that Brashear became doesn’t have any records going back that far.


When we first looked through the scope, we thought the views were terrible, which surprised us. However, as we were cleaning the lens cell, someone noticed subtle pencil marks on the edges of the two lens elements, indicating how they were supposed to be aligned with each other. Once we fixed that, and replaced the 8 or so paper tabs with three blue tape tabs, we found it produced very nice views indeed!

The focuser accepts standard 1.25″ eyepieces, and the focuser slides very smoothly (once we got the nasty, flaky corrosion off as delicately as possible and sprayed the metal with several coats of clear polyurethane). The workmanship is beautiful!

Top: tiller for hand control of right ascension. Middle: counterweight bar (machined by me to screw into the mount) with clamps to hold weights in place. Bottom: detail of 1.25″ rack-and-pinion focuser.

We have not cleaned the mechanical mount, or tried it out, but it does appear to operate: the user turns a miniature boat tiller at the end of a long lever to keep up with the motions of the stars.

The mount and cradle (with size 12 feet for scale)

The counterweight rod was missing, so I machined a replacement, which has weight holder clamps like you see in gymnasiums. Normal Barbell-type weights with 1 inch holes fit well and can be adjusted with the clamps.

Unfortunately, the whole device is rather heavy, and we already own a nice 6″ f/15 refractor made by Jaegers, as well as some Schmidt-Cassegrain telescopes that also have long focal lengths. Putting this scope on its own pedestal, outside our roll-off roof, with adequate protection from both the elements and from vandals, or figuring out a way to mount it and remove it when needed, are efforts that we don’t see as being wise for us.

Did I mention that it’s heavy? The OTA and the mount together weigh roughly 100 pounds.

However, it’s really a beautiful, historic piece with great optics. Perhaps a collector might be interested in putting this in a dome atop their home or in their office? Or perhaps someone might be interested in trading this towards a nice Ritchey Chretien or Corrected Dal-Kirkham telescope of moderate aperture?

Anybody know what might be a fair price for this?

Guy Brandenburg

President

The Hopewell Observatory

Some more photos of the process and to three previous posts on this telescope.

Partway through cleaning the greenish, peeling, grimy layer and old duct tape residue with a fine wire brush at low speed to reveal the beautiful brass OTA.
This shows the universal joint that attaches to the ’tiller’ and drives the RA axis
Do you see the secret mark, not aligned with anything?
Aluminum lens cover and cell before cleaning
Lens cell and cover, with adjustment screws highlighted, after cleaning
It works!

Some WW2 or Cold-War-Era Aerial Surveillance Cameras

02 Wednesday Sep 2020

Posted by gfbrandenburg in astronomy, History, Hopewell Observatorry, Optics, science, Telescope Making, Uncategorized

≈ 2 Comments

Tags

Aerial reconnaissance camera assemblies

(Think U2 spyplanes.. )

Hopewell Observatory has three WW2 or Cold-War aerial spy camera optical tube assemblies, including a relatively famous Fairchild K-38. No film holders, though. And no spy planes. The lenses are in good condition, and the shutters seem to work fine.

We would like to give them away to someone who wants and appreciates them, and can put them to good use. Does anybody know someone who would be interested?

They’ve been sitting unused in our clubhouse for over 20 years. Take one, take two, take all of them, we want them gone.

We are located in the DC / Northern Virginia area. Nearby pickup is best. Anybody who wants them shipped elsewhere would obviously need to pay for packaging and shipping.

Here are some photos.

This one is labeled K-38, has a special, delicate, fluorite lens in front, and is stamped with the label 10-10-57 – perhaps a date. The shoe is for scale.

IMG_2009
IMG_2010
IMG_2012
IMG_2014
IMG_2017
IMG_2018
IMG_2020
IMG_2022
IMG_2024

 

The next two have tape measures and shoes for scale.

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hopewell jan 2013 036

 

Let me know (a comment will work) if you are interested.

A neat geometry lesson! And a rant…

13 Thursday Feb 2020

Posted by gfbrandenburg in education, flat, History, Math, Optics, teaching, Telescope Making, Uncategorized

≈ Leave a comment

Tags

apps, computer, computer-managed instruction, geometry, kaleidoscope, Math, Mirror, programs, reflection, school

Here is some information that teachers at quite a few different levels could use* for a really interesting geometry lesson involving reflections involving two or more mirrors, placed at various angles!

Certain specific angles have very special effects, including 90, 72, 60, 45 degrees … But WHY?

This could be done with actual mirrors and a protractor, or with geometry software like Geometer’s Sketchpad or Desmos. Students could also end up making their own kaleidoscopes – either with little bits of colored plastic at the end or else with some sort of a wide-angle lens. (You can find many easy directions online for doing just that; some kits are a lot more optically perfect than others, but I don’t think I’ve even seen a kaleidoscope that had its mirrors set at any angle other than 60 degrees!)

I am reproducing a couple of the images and text that Angel Gilding provides on their website (which they set up to sell silvering kits (about which I’ve posted before, and which I am going to attempt using pretty soon)).

At 72º you see 4 complete reflections.

When two mirrors are parallel to each other, the number of reflections is infinite. Placing one mirror at a slight angle causes the reflections to curve.

 

https://angelgilding.com/multiple-reflections/

===========

Rant, in the form of a long footnote:

* assuming that the teacher are still allowed to initiate and carry out interesting projects for their students to use, and aren’t forced to follow a scripted curriculum. It would be a lot better use of computers than forcing kids to painfully walk through (and cheat, and goof off a lot) when an entire class is forced to use one of those very expensive but basically worthless highly-centralized, district-purchased computer-managed-instruction apps. God, what a waste of time – from personal experience attempting to be a volunteer community math tutor at such a school, and also from my experience as a paid or volunteer tutor in helping many many students who have had to use such programs as homework. Also when I was required to use them in my own classes, over a decade ago, I and most of my colleagues found them a waste of time. (Not all – I got officially reprimanded for telling my department chair that ‘Renaissance Math’ was either a ‘pile of crap’ or a ‘pile of shit’ to my then-department head, in the hearing of one of the APs, on a teacher-only day.

Keep in mind: I’m no Luddite! I realized early on that in math, science, and art, computers would be very, very useful. I learned how to write programs in BASIC on one of the very first time-share networks, 45 years ago. For the first ten years that my school system there was almost no decent useful software for math teachers to use with their classes unless you had AppleII computers. We had Commodore-64’s which were totally incompatible and there were very few companies (Sunburst was one) putting out any decent software for the latter. So when I saw some great ideas that would be ideal for kids to use on computers to make thinking about numbers, graphs, and equations actually fun and mentally engaging, often I would have to write them my self during whatever free time I could catch, at nights and weekends. Of course, doing this while being a daddy to 2 kids, and still trying to teach JHS math to a full load of students (100 to 150 different kids a day at Francis Junior High School) and running a school math club and later coaching soccer. (I won’t say I was a perfect person or a perfect teacher. I believe I learned to give better math explanations than most, didn’t believe that you either have a ‘m,ath gene’ or you don’t, at times had some interesting projects, and at times was very patient and clear, but had a terrible temper and often not good at defusing things. Ask my kids or my former students!) Later on, I collaborated with some French math teachers and a computer programmer to try to make an app/program called Geometrix for American geometry classes that was supposed to help kids figure out how to make all sorts of geometric constructions and then develop a proof of some property of that situation. It was a failure. I was the one writing the American version, including constructions and tasks from the text I was currently using. There was no way I could anticipate what sorts of obstacles students would find when using this program, until I had actual guinea pig students to use them with. Turns out the final crunch of writing however many hundreds of exercises took place over the summer, and no students to try them on. Figuring out hints and clues would require watching a whole bunch of kids and seeing what they were getting right or wrong. In other words, a lot of people’s full time job for a long time, maybe paying the kids as well to try it out so as to get good feedback, and so on. Maybe it could work, but it would require a lot more investment of resources that the tiny French and American companies involved could afford. We would have really needed a team of people, not just me and a single checker.

I find that none of these computer-dominated online learning programs (much less the one I worked on) can take the place of a good teacher. Being in class, listening to and communicating logically or emotionally with a number of other students and a knowledgeable adult or two, is in itself an extremely important skill  to learn. It’s also the best way to absorb new material in a way that will make sense and be added to one’s store of knowledge. That sort of group interaction is simply IMPOSSIBLE in a class where everybody is completely atomized and is on their own electronic device, engaged or not.

Without a human being trying to make sense out of the material, what I found quite consistently, in all the computerized settings, that most students absorbed nothing at all or else the wrong lessons altogether (such as, ‘if you randomly try all the multiple choice answers, you’ll eventually pick the right one and you can move on to some other stupid screen’; it doesn’t matter that all your prior choices were wrong; sometimes you get lucky and pick the right one first or second! Whee! It’s like a slot machine at a casino!).

By contrast, I found that with programs/apps/languages like Logo, Darts, Green Globs, or Geometer’s Sketchpad, with teacher guidance, students actually got engaged in the process, had fun, and learned something.

I find the canned computer “explanations” are almost always ignored by the students, and are sometimes flat-out wrong. Other times, although they may be mathematically correct, they assume either way too much or way too little, or else are just plain confusing. I have yet to detect much of any learning going on because of those programs.

Mining at the Observatory (sort of…)

03 Friday Jan 2020

Posted by gfbrandenburg in Hopewell Observatorry, Telescope Making, Uncategorized

≈ Leave a comment

Tags

jackhammer, maintenance, masonry, observatory

We have been concerned with the status of some of the columns that are part of the roll-off-roof of the Hopewell Observatory, so we decided to remove a couple of courses of cinderblock to see what was inside. It turned out to be built much more sturdily than they appeared. and removing those two layers of cinderblock ended up being a much harder job than we expected. We had to build a very strong ‘crib’ to hold the upper part of the 9-foot-tall column in place while we removed the lower foot-and-a-third.

In the video, you see me using a small hand-held air-hammer with chisel to clean up the underside of the upper part of the column, so that the new solid cinderblocks can be mortared into place. The buzzing noise you hear is the air compressor.

We didn’t realize there was rebar (reinforcing iron bars) and concrete poured into most of the ‘cells’ of the 16″ by 24″ columns. Now we do.

How I left it: two solid blocks and some plywood in case our cribbing and jacks give way
How I left it: two solid blocks and some plywood in case our cribbing and jacks give way
You are looking up towards the majority of the column
You are looking up towards the majority of the column

(In the summer of 1970, between my junior and senior years, I found a job in Brooklyn working on a rodding truck for the local electric power utility, Con Edison — a hard and dirty job that made me itch constantly because of all the fiberglass dust that was scraped off the poles we used to clean out the supposedly empty, masonry, electric conduits that went from one manhole to the next. I guess I pissed off our truck crew’s supervisor, so the very day that I was about to quit to go back to college, I was told that I was being transferred to a jack-hammer crew, where I probably would have gone deaf. This woulda been me, except I quit)

Image result for jackhammering

 

After that was done, I trimmed some of the trees to the west. Constant struggle with the shrubbery!

 

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