Telescope Making – Page 2

In the end it is a Celestron C8 telescope drive and forks containing custom electronics, a Meade heavy duty wedge from an LX-90, a hand-made tripod, holding a Televue 76mm APO telescope, using a Vixen style dovetail base, with a Baader film solar filter.

It is tempting to call it Frankenscope after the similarities with the classic monster.

Hodgepodge setup on the side of Mauna Kea with the TV-76mm and Telrad on the plate

To further add the the Mary Shelley plot similarities, much of this was revived from the junk pile. I very nearly decided to toss the drive and fork, they were that bad, peeling paint and rusty bolts. A great deal of work was necessary to re-animate these components.

The wedge came from a telescope that was killed in an unfortunate incident with an aquarium heater. The heater was used to de-humidify the OTA and prevent fungus on the optics. Note: Aquarium heaters are not made to operate out of water.

Several new aluminum parts were machined from scraps, some of which were scavenged when the observatory shop was being cleaned out and a lot of metal stock was tossed.

Many of the electronic components used to build the drive corrector were also scavenged parts from dead electronics, this includes the 1.8432MHz crystal that forms it’s beating heart. This heartbeat keeps the mount turning at exactly sidereal rate.

Yeah, you could call it Frankenscope.

But I will call it Hodgepodge.

Tripod Legs — The legs and other parts of the field tripod with a fresh coat of polyurethane

Tripod Parts — Parts for the Hodgepodge field tripod drying in intense tropical sunlight

Extendable Tripod Foot — The extendable foot section for the Hodgepodge field tripod

Tripod Head — The Meade wedge bolts to a Celestron field tripod head without modification

Old School Drive Corrector

Telescope clock drives from the 1980’s or earlier often used AC synchronous motors. These commonly available AC motors are used to power timeclocks, record player turntables, and telescopes, anyplace a motor needed to run at a very accurate speed.

Sidereal Drive Platform — A Celestron telescope drive configured as a sidereal rate tracking camera platform

The speed of a synchronous motor is set by the frequency of the powerline, in North America and many other places this is 60Hz. As the frequency must be synchronized for every power station on the grid the frequency is quite accurate, a feature exploited by clockmakers and telescope builders. Once found everywhere these motors are less common, but are still around.

Drive Correctors

It was the common use of these motors in telescope drives that led to the invention of the drive corrector, a device that was once a required piece of kit for serious amateur astronomers. Drive correctors like this were needed when operating from a battery at some remote location, generating AC from a 12Vdc car battery.

You also needed a drive corrector for guiding while doing astrophotography. The corrector could speed up or slow down the telescope drive a bit to correct the telescope drive speed and stay on target, something not possible with the fixed 60Hz of the mains supply. Thus the term drive corrector.

ATM Gallery

Gluing the Mirror Box — Gluing the mirror box for Deep Violet, and 18″ f/4.5

Mirror Cell — The 18 point mirror cell, built to the plans from Barry & Kriege

The Strap — The primary mirror support strap

Ground Board — The ground board with center pivot and teflon pads in place

Drilling a Pocket — Drilling a pocket to accommodate a carpet pad in the side of the rocker box

Nearly Ready — Deep Violet fully assembled and nearly ready for dark

Deep Violet at Sentinel, Arizona for the 2015 Pierre Schwarr Star Gaze

Axis — Detail of the tripod head, latitude adjustment and the RA and declination axis

Set Up — Primero setup at Jarnac Observatory among a friendly crowd of other telescopes

Binocular Parts — Stripping and cleaning the 14×100 binoculars

Celestron Cometron in Parts — A completely disassembled Celestron Cometron telescope

Upper Truss Clamp — Detail of the upper truss tube with the lever type latch

Threadsert — Detail of the brass threadserts used to hold the lower truss clamp

12.5" Dobsonian — A 12.5″ dobsonian telescope after the refit

Machining the Mirror Cell — Machining the mirror cell from a piece of scuba tank

Empty Mirror Cell — The mirror cell prior to installing the primary mirror with the focus knob at the back of the strut

Mirror Mount — A very standard design for the mirror mount

Front View — A front view of Makaʻiki ready to observe

Strut Extended — Makaʻiki with the main strut extended for use

First Light for Makaʻiki — Makaʻiki under the stars for the first time at Hale Pōhaku on the side of Mauna Kea

Pier Forms — The forms for the pier upright filled and leveled

Pouring the Upright — Bill Lofquist pouring concrete into the upright part of the pier

Complete Pier — The completed pier with a telescope atop

Orange Tube Corrosion — Looking at what remains of the paint on an old Celestron C8 orange tube telescope

Stripping the Orange — The orange paint just crumbles away under a few sweeps of a power sander

Ready for Paint — Parts of the mount prepped and taped for painting

Drying Paint — Paint drying on the front and rear castings of the old orange tube

Restored C8 — A restored Celestron C8 on a similarly restored TeleVue Renaissance mount.

Transit Telescope — The C8 set up along the old Saddle Road for Mercury Transit

Secondary Cage — Re-assembling the secondary cage on the 20″ Obsession. The truss tube clamps still need to be cleaned up and re-installed, same with the focuser.

Rusted Hardware — The rusted hardware removed from a 20″ Obsession telescope

Fixing the Clamp — Opening up the truss tube clamps by widening the slot with a hacksaw.

Secondary Mount Fix — A fix for the secondary mount

Primary Mirror from the Back — Installing the primary mirror. This is a Galaxy Optics 20″ f/4. Oddly enough Sky Hudek, the son of John Hudek, the owner of Galaxy is a good friend and dive buddy.

Trunk Handles on the Rocker Box — Trunk handles added to the rocker box to make picking it up and loading it in a vehicle easier. They are mounted just high enough to avoid the wheelbarrow handles when installed.

20" f/4 Obsession — 20″ f/4 Obsession #004 fully assembled for the first time in over a year. Ready for alignment and use!

The Dobsonian Telescope

In restoring a 20″ Obsession telescope I found myself pulling a book from the shelf that had not been opened in a while. David Kriege and Richard Berry’s The Dobsonian Telescope – A Practical manual for Building Large Aperture Telescopes is a book I once read cover to cover.

The information here was critical in the success of my building Deep Violet, my 18″ telescope. Within the pages of this book are plans and drawings of the important bits as well as detailed discussions of what does, and does not work, when building a telescope.

The Dobsonian Telescope is the primary reference for those building large amateur telescopes. This book, along with the design revolution that went with it, put large telescopes in the hands of countless amateur astronomers. These telescopes extended the capabilities of amateur observers immensely, allowing spectacular views of deep space objects that were only fuzzy smears in the eyepiece before. Want to see the spiral arms of galaxies? A 20″ telescope can do that!

As I perused my well thumbed copy I was surprised to find bits of my own telescope plans used as bookmarks. There was dust on the top of the pages, but I still remembered where I disagreed with Kriege in the dimensions of the mirror box, or how to place the truss tube clamps. I may have deviated from the plans shown here in some aspects, but in other parts of the design I directly used the dimensions shown in the book.

So many old memories, good memories. Pursuing an art that has been around for four centuries, combining bits of wood and glass to make an instrument that can reveal our universe. Sure you can simply buy a very good modern telescope. But it is hard to overstate the pleasure of building one yourself. This is an art that can still be done in a garage, with tools available at the local hardware store, with results that can rival or even surpass something purchased from a catalog.

Obsession in the Dusk

20" f/4 Obsession Telescope — The restored 20″ Obsession telescope set up at Hale Pohaku on the side of Mauna Kea

Restoring an Obsession

Obsession Telescopes are something of a standard in the astronomy community. David Kriege was one of the first to start building truss tube dobsonian telescopes commercially, bringing portable large aperture telescopes to the astronomy community. These telescopes were a bit of a revolution in the pursuit, with sizes unreachable only a decade before, when a 10″ or 12″ telescope was considered big. When I built my 18″ it is David Kriege’s book I used for much of the design, following in the footsteps of so many amateur astronomers.

A 20″ f/4 Obsession donated to the observatory has presented a challenge and an opportunity. The telescope was the prized possession of Bob Michael having been ordered new directly from Obsession. The telescope is serial number 004 with a manufacturing date of June 1st, 1990. As David started Obsession Telescope in 1989, this is a very early example of his work. For many years Bob and his wife used this telescope to observe, completing the Herschel 400 and other observing projects. Unfortunately he was forced to give up astronomy due to age and glaucoma, donating his equipment to the observatory.

Continue reading “Restoring an Obsession”

Clamps

Rusted Hardware

Fungus on Glass

The tropical environment of Hawaiʻi is not kind to optical instruments. Tropical humidity can cause a host of issues ranging from corrosion of metal parts to decay of wooden and cardboard telescope structures. For those of us who build and use small telescopes the issues of tropical heat and humidity are rather concerning.

Worst of all is the fungus. Impressively there are species of fungus that can grow and thrive on clean optical surfaces. It is hard to imaging a more hostile place to grow, seemingly devoid of nutrients and the moisture necessary for life.

I have seen camera lenses lost to the white fungus. A friend once showed me a Canon 70-200 f/2.8 L, a $2000 lens, with fungus covering internal elements. Even on the “dry side” of Waimea the humidity was high enough to allow fungus to destroy this lens.

The problem is not an issue on the summit of Mauna Kea. The high altitude air typically exhibits a relative humidity of less than 10%. Several references note that a humidity of above 70% is needed to promote fungal growth on optics. We see no issues with fungal damage to the mirrors or instruments on the big ‘scopes.

Below the tropical inversion layer (about 6-7k feet) it is another issue entirely. Near sea level, where most of us live, humidity can remain above 80% much of the year. The warm and humid conditions of these islands are idea for growing anything, including the omnipresent fungal gardens that create the smells of a tropical landscape. Fungus is inescapable in this world, the spores drift on the wind and an stay dormant for decades, anywhere conditions are suitable fungus will grow.

The possibility of equipment damage was a major element in our buying a house. Waikoloa is located within one of the driest areas of the island. The humidity typically hovers in the 50’s, dry enough that I have had no issues with the multiple telescopes stored in the garage. Still, I do inspect stored equipment periodically, looking for the dreaded white fungus or other damage wrought by this tropical climate.

It is not a single species of fungus responsible for the problem. Apparently quite a few species are able to colonize an optical surface. Looking through the literature I find referenced to multiple species that can grow on optical glass…

The fungi which grow in optical instruments belong to the groups Phycomycetes, Ascomycetes and Fungi Imperfecti. The following species were frequently isolated from instruments which had been in New Guinea: Penicillium spinulosum, Thom.; P. commune, Thom.; P. citrinum, Thom.; Aspergillus niger, Van Tiegh.; Trichoderma viride, Pers. ex-Fr.; Mucor racemosus, Fres.; and M. ramannianus, A. Moeller. So far, Monilia crassa has not been isolated from Australian instruments, although Dr. W. G. Hutchinson (5) of the United States, found this to be a common species in the Panama zone, and it has also been recorded as frequent in West Africa by Major I. G. Campbell. – J.S. Turner, et al.¹

I admit that the fungus can be pretty, in an odd sort of way considering the damage. Under a microscope it appears lacy, the mycelium fibrils growing across the glass in search of more nutrients to support the colony. In the center small round fruiting bodies are the launching point for new fungal spores.

I recently had another round of battle with fungus while restoring a collection of instruments that had been stored in a garage on the side of Hualalai. The high humidity had wrought impressive damage on both the optics and metal components of the telescopes. And there is fungus! Found in the eyepieces and on the telescope mirrors. During the cleaning and restoration of the instruments I found it necessary to completely dismantle many optical assemblies just to remove and kill the fungus. I some cases I was in time, but not completely, it is not without regret that I throw a $400 eyepiece into the trash.

Dealing with the fungus is imperative, cleaning and killing the growth before severe damage can be done may save the equipment. If the growth is severe enough the glass surface and the coatings can be damaged. Apparently the fungi can excrete hydrochloric acid, etching the surface and creating permanent damage.

Minor damage may not be enough to ruin the device. It actually takes a great deal of damage to appreciably affect the performance of most optics. A few small specks of damage remaining on the surface after cleaning may not be noticeable. Inspection of each spot of damage with a microscope can be useful, Sometimes it is clearly damage of the surface and irrepairable. I have also found hard deposits that at first glance appeared to be damage under the core of fungal colonies that remained after cleaning. These may be removed using a soft wooden tool like a toothpick or chopstick.

Killing the fungi requires a solvent that will both kill the fungus while not damaging the optical surface. I find references to both alcohol as well as other solvents. A mix of 50/50 hydrogen peroxide and ammonia is recommended by some references. Along with cleaning the glass I am careful to soak all of the structural elements as well. The tube, the spacers and lock-rings can all harbor minuscule colonies or spores awaiting suitable conditions to grow again.

Optical fungicide solutions tend to be expensive and hard to obtain, but they are available from some optical equipment manufacturers. Alternatively, you can use a 50/50 mix of hydrogen peroxide (H2O2) and ammonia (NH3). Usually, 5 ml of each is adequate (10 cc in total). Mix just prior to use and do not store the mixed product. – Ismael Cordero, Community Eye Health Journal²

Living in a warm humid environment one must be vigilant and ready to deal with issues when found. Examine optics regularly, keep a can of WD-40 next to the tool box (and use it), store optics and electronics with plenty of ventilation and reduce the humidity to well below 70% if needed. Extra vigilance to preserve valuable equipment is the price of living in paradise.