Category Archives: Optics

First Time Installation of OnStep Board with NEMA23 Stepper Motors in Ealing Mount at Hopewell

03 Monday Jan 2022

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A 3-minute video of the results of our first-time installation of something called an OnStep conversion. We are replacing the telescope drive of a venerable but beautifully machined telescope mount, located at a small group-owned observatory called Hopewell, atop a ridge called Bull Run Mountain*.

It’s alive!

Sorry, it’s not the greatest or clearest video. Also, I mistakenly state at about 0:25 in the video that the right ascension axis was turning at 12 RPM, but it’s not: I should have said 5 RPM, or one revolution in 12 seconds.

You can hear some stuttering of one of the motors. You are right, that is not a good sound. We were able to get it to stop and start making that noise and motion by adjusting the precise positioning of some of the gears. It will take some time and experimentation to get that perfect.

Later on (not captured in this video), when I was trying to slew in the declination axis at the highest speed possible, the stepper motor once again screamed and halted. I’m hopeful that all of those problems can be fixed by doing one or more of these things:

  • 1) adjusting the fit of all those gears;
  • (2) changing certain parameters of microstepping and current to the stepper motors in software; and/or
  • (3) increasing the voltage to the board from 18 VDC to 24 VDC.

I’ll need to test things out on my desk at home, using the same OnStep board, but without the gears and timing belt. (That stuff was a royal PITA to remove screw back into place, and none of us have any desire to take them back out again!) I have some identical extra stepper motors that I can test out, with gloved hands, to see if it is possible to stop the motors from turning. Right now, I still don’t think they are putting out the amount of torque needed.

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*Yes, that famous Bull Run of Civil War fame is not far away. However, our observatory is named after a different geological feature, namely the Hopewell Gap that cuts through the hard rock of Bull Run Mountain right about where where the creek called Little Bull Run begins.

If you are reading this, you probably know that serious amateur, and all professional, astronomical telescopes (except for Dobs) are generally driven by ‘clock drives’ so that the object one is viewing or photographing stays properly centered as the earth rotates imperceptibly beneath us. The original Ealing motor drive at Hopewell, while turning excellent Ed Byers gears, had been an intermittent problem ever since it was delivered to the University of Maryland about 50 years ago. It was in fact not operational when they sold it to us for a pittance about 30 years ago. (If you go to the University of Maryland Observatory site I linked to, the scope we have now is the one in the center of the 1970s – era photo labeled ‘Figure 4’.)

Bob Bolster, one of the founding members of Hopewell observatory, disassembled the drive, modified it considerably, and got it working again, several years before I joined the group. The scope worked, off and on, with a very complex clutch system for ‘fast’ and ‘slow’ movement of the scope, for most of the rest of the last 25 or so years, except for occasional motor burnouts and clutch replacements. Also unfortunately, the optics on the original 12″ Ritchey-Chretien telescope, were not very good, so we removed them, had them in an attic for many years, re-tested them, and finally sold the glass and the holders, for a pittance, to someone in Italy who wanted to try to re-figure them.

This was originally a ‘push-to’ telescope, meaning that one loosened up two Byers clutches (one for each axis), located the desired target in the sky, tightened the two clutches, did some fine tuning with an electric hand paddle to center the target more precisely, and then allowed the telescope drive to then keep the object in the center of the eyepiece or camera field of view as long as one wanted. It originally came with metal setting circles (basically, finely-made protractors that showed where the scope is pointing vis-a-vis the polar and declination axes), which made finding targets possible, though not trivial!

About 15 years ago, Bolster (with some help from me) installed Digital Setting Circles, which used a rotary encoder on each axis, along with a small hand-held computer and screen display, to allow one to select a given target; the DSC hand paddle’s display then would indicate how far one should rotate the scope along those axes to find the desired celestial object; when it was in the field of your widest eyepiece, one used the hand paddle to center it more precisely.

Converting this scope to an OnStep drive will, I hope, make this a Go-To scope in which one can command the telescope to aim at whatever target one desires.

Unfortunately, right now, the fastest it seems to rotate in Declination, with no load whatsoever (all scopes have been removed, so no balance or inertia problems) is about one degree per second. So doing a 180-degree turn in a North-South direction would take a full three minutes. A 30-degree turn would take 30 seconds. Can we make this a bit faster? I hope so.

I wasn’t able to really slew in right ascension (East-West) because the counterweight box, even though empty, seems to require too much torque to rotate right now.

Bolster passed away a few years ago, and this summer, the moment I had been dreading finally arrived: the drive on the Ealing died again, and his amazing skills and tenacity in fixing such problems was gone with him. What’s more, in his final years, his incurable, chronic idiopathic neuropathy made it literally impossible for him to speak, and even typing email responses to the rest of us took a very long time. So most of his wealth of knowledge and experience died with him.

As indicated in my earlier posts (here, here, here, and here), with help from others, I was able to take the two motor setups for the two axes out from the mount and get them working again on my workbench in their original format. I was even able to order and install material for the clutches. However, I discovered that one needed to adjust the clutches very, very precisely, or else they wouldn’t work at all.

I couldn’t figure out how to do that.

And nobody else who belongs to our observatory volunteered to help out, except for removing the scopes and drives from their former positions inside the mount.

So I decided to convert to a totally different type of telescope drive, one inspired by the Arduino boards and 3-D printers. A group of really smart and resourceful hobbyists (engineers?) designed a system around the Arduino environment that uses inexpensive off-the-shelf printed circuits and complex sub-boards and components, used originally mostly in the 3-D printers that have become so popular, to drive at telescope just the way astronomers want them to be driven.

Apparently, there have been many, many OnStep successes, but what we are doing may be the largest and most massive mount to date that has done such a conversion.

I was warned that the entire process would take some months. Those warnings were correct. But that’s OK. I’m retired, I have time, and I have access to tools and people who are interested in helping. What’s more, I have learned a whole lot about modern electronics, and my soldering skills are much better than they ever were.

I’d again like to thank Alan Tarica (who’s physically helped a **tremendous** amount), Prasad Agrahar (who first showed me the OnStep conversions he had done on a much smaller equatorial mount), Howard Dutton (who first conceived and implemented OnStep), Ken Hunter (who made and **donated** to us a complete, functional OnStep board together with all sorts of accessories and walked me by phone and video through many of my fumbling first steps), Khalid Bahayeldin, George Cushing, and many others.

Progress and Problems with an OnStep Conversion of a High-Quality 1970’s Telescope Drive

31 Friday Dec 2021

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I have made a lot of progress over this winter break in converting the 50-year-old Ealing telescope mount at the Hopewell Observatory, as you can see in this video.

We are swapping out an electro-mechanical “dumb” drive that failed, in favor of a modern, solid-state one built in the Arduino environment. If it all works out as planned, this mount will be able to slew to any target and keep the target steady enough for astrophotograpy. I hope.

With a project like this, with delicate electronics that can easily get fried, I believe that having spare parts on hand is a good idea. The main board is pretty cheap: under $100, completely assembled, and the motors were about $30 each. We have spare stepper motors, spare stepper drivers, and a total of three main MaxESP OnStep boards.

Except that two of them (the ones we purchased from George C) don’t work at all, and I don’t know why. The one that Ken Hunter built and **donated** to us works just fine, after I did the required tweaking of various settings inside the Smart Hand Controller or SHC and inside a CONFIG.H file in the Arduino programming environment. And added the gears and belt.

I see almost no serious differences between George’s boards and Ken’s board. I am confident the problem is not my wiring or soldering, and it’s not the fact that George’s boards have RJ45 jacks, but what it is, I have no idea.

This is my second build of the connections between the stepper motor and the worm gear.

Without the help of Ken H, Howard Dutton, another Ken, Alan Tarica, Prasad Agrahar, and Khaled Bahayeldin, I never would have gotten this far. I am very appreciative of the amount of work that went into programming all of the many parts of the OnStep project as a whole. However, I found the OnStep Wiki rather confusing for beginners, and I hope to help them make it clearer in the future.

You can probably see that there is a good bit of wobble in the gears that involve the belts. That is probably because I failed to get the gears perfectly flush against the lathe chuck when I was enlarging their central holes from 5 mm to 1/4 inch despite using a dial indicator with a magnetic base to center it. I think I will need to order a new set of gears that have a 1/4″ axle hole already made at the factory. I don’t think I can do any better than I did, and that wasn’t good enough.

The reason for having the gears and belts is something to do with microstepping on the stepper motors that I really don’t understand. OnStep experts told me that the OnStep board, drivers, and steppers simply cannot handle gears that are 1 : 20 : 359. So we added a 3:1 toothed-gear-and-belt system so that the ratios are now 3 : 1 : 20 : 359. That set of ratios seems to make the steppers happy. (These motors have 200 steps per rotation, and are being currently driven at a rate of 1/16 of a step.) They don’t scream and stall any more, but the wobbly gears will probably translate into periodic error that one can see in the eyepiece or on long exposures with some kind of camera.

My next step is to take this entire apparatus up to the Hopewell Observatory itself and see what happens when I install them in the Right Ascension and Declination drives.

Then, we need to repair the electrical supply for the roll-off roof.

Then we have to put the telescopes back onto the mount.

Then, and only then, can we try having a “First Light” with the new motor pushing a very nice Ed Byers drive in an big, old, and very well-built university-grade telescope mount.

It’s Not Rust! It’s Just Grease!

19 Sunday Dec 2021

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Here is a photo of the inside of the declination axis of the Ealing mount at Hopewell Observatory.

The gears you see were made about 50 years ago by the Ed Byers company, who continue to produce some of the finest gears anywhere. The periodic error on this mount is very, very low, which is a Good Thing, and why we want to keep it and just upgrade the old drive. As you can see in a previous post, the old system had a finicky clutch drive that had caused a lot of problems, but worked very well indeed when it worked properly.

I am working to replace it with a more modern, reliable and user-friendly, namely an OnStep ‘build’.

The friendly and helpful folks at the OnStep project were asking for a picture showing how the existing Byers drive was put together. I hope these four photos help.

In the first photo, notice the greasy worm gear at the bottom left. It was removed from the mount, along with the old motors, and is sitting on my desk (with the old grease cleaned off), directly coupled to the stepper motor, which connects to one of the OnStep boards (in the wood-and-black aluminum box). In the second photo,

The black anodized bracket in the second photo holds the motor and the worm gear rigidly together. The bracket bolts into a place in the mount (not shown). It took a bit of work to get the stepper motor and the worm gear lined up within a couple of thousandths of an inch, but it’s done. Prasad turned me onto those cool little universal joints that permit one to connect items that don’t match perfectly.

20 turns of the worm gear, times 359 teeth on the big gear, means that it takes 7,180 turns of the stepper motor to make one full revolution of this declination axis or of the right ascension axis, which is identically mounted. (Not that you would want to go about spinning your telescope very far on either axis!)

So 19.97 turns of either motor make the scope travel 1 degree (7180 divided by 360).

And since our stepper motors make 200 steps in one revolution of the worm gear, it takes about 3994 motor steps to make the scope turn by that one degree (the last result, times 200).

Or if you are micro-stepping by, say, the rate of one sixteenth of a step, then by my calculations it will take 63,911 microsteps to turn by that degree (the last result, times 16). And that seems to be outside the range of permissible microsteps for these stepper motors, perhaps causing them to scream in protest. (I swear, that’s what it sounds like!)

From left to right: A spare OnStep board inside its wood-and-aluminum project box; the NEMA23 stepper motor on its bracket; a universal joint; a big bearing; the first worm gear (now cleaned off)

It appears that Khaled and Prasad might be correct: I might need to add a toothed gears and a belt to this arrangement to reduce that last number (63,911) by some factor. For very little money I just ordered a pair of such things, designed for 3-D printers and other computer-controlled machines. It will have 60 teeth on the motor and 20 teeth on the worm gear, and then the above would instead have only 21,304 microsteps to turn one degree. (No wonder they protest!) Once again I’ll have to disassemble the motor and drive bracket and do a bit of machining. A drill press and a punch will be fine.

The last two photos give some more detail on how the old drive system worked.

Close up of worm gear driving a toothed gear wheel that drives another worm gear that drives the right ascension axis
One of the original drive motor and clutch assemblies in place, inside the mount. All those gears have now been removed.

Correct weight of the mystery glass

13 Wednesday Oct 2021

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

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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

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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.

First Telescope Making Class Since March of 2020!

15 Wednesday Sep 2021

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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

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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.

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

05 Monday Oct 2020

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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 in astronomy, History, Hopewell Observatorry, Optics, science, Telescope Making, Uncategorized

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(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.

 

The next two have tape measures and shoes for scale.

 

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

A neat geometry lesson! And a rant…

13 Thursday Feb 2020

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

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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/

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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.