Testing a Mirror

As I have observed lately, most of the small telescope mirrors available right now are out of China, most of those produced by one company, Guan Sheng Optical or GSO. If you want a small mirror, say a 6″ or 8″ mirror, there is not a lot of choice, the mirror makers in the US generally do not do anything smaller than 10″.

Foucault knife edge test
A textbook Foucault knife edge test image on a 6″ f/4 mirror

The GSO mirrors range from decent to pretty bad, with no way of knowing what you will get when you order, just luck of the draw.

But how do you tell?

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My Telescope Sings to Me

OK, I did not expect this.

At the telescope in the driveway again
At the telescope in the driveway again

I have been observing from my driveway each evening this last week now that the Moon has left the evening sky. Pleasant sessions wandering through the stars and clusters of Scorpius, Sagittarius, and Ara.

The week has also featured gentle trade winds at the house, resulting in fickle breezes around the telescope which is mostly in the shelter of the house. I get some manini gusts that make it around the garage that really do not bother me but do keep the mosquitoes down.

These breeze have created an unexpected phenomena, they make my telescope sing to me.

It is a gentle and resonant low B note as the breeze plays past the front of the telescope. Much like blowing across the top of a beer bottle, the tube of the telescope resonates with the breeze. Apparently a Cave Astrola 8″ f/6 telescope is a tenor.

Sometimes quiet, sometimes quite notable, I listen to the telescope hum while I look up the next cluster to observe.

Now if you excuse me I need to chase the pigs out of the yard… Again.

Christmas Telescopes

We just received the Costco Christmas sales mailer. Every year there is a telescope featured, promoted as a gift. Not just slightly featured either, but included on the front page of the flyer, the first thing you see when you pick the mailer up.

Celestron Astromaster 130EQ
A typical inexpensive telescope, the Celestron Astromaster 130EQ

The telescope this year is a Celestron Astromaster 130EQ, the typical small reflector on an equatorial mount. The deal includes several eyepieces, filters, and a cell phone adapter for afocal photography.

Those of us with long practical experience just cringe when we see such telescopes. These cheap telescopes are usually more of a frustration to would be amateur astronomers than useful. Cheap ‘scopes have deterred more folks from the hobby than we will ever know.

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Unsafe Solar Filters on EBay

I though these things were gone!

Eyepiece mounted solar filter
DO NOT USE! A Solar filter meant to thread into a 0.956″ telescope eyepiece.
But no, in the world of cheap e-commerce, any product can be found, even those that are notably unsafe.

What are we discussing? Eyepiece style solar filters that screw into the threads on the bottom of the eyepiece, not at the front of the telescope like proper solar filters.

I actually have one of these things, found in a kit of equipment I was given. A bright red and very cheap pot metal casting with a small glass filter. I have never attempted to actually use it, I keep it as a example of the bad and the ugly. It is a vintage bit of gear, the type that was included with inexpensive Japanese refractors of the 60’s and 70’s, sized to be used with the small 0.965″ eyepieces of the era.

An eyepiece style solar filter available on EBay
An eyepiece style solar filter available on EBay
To my surprise I find out these things are still around… I was shopping for an inexpensive solar filter for a small telescope when I came across these eyepiece style filters on EBay. They are cheap too, less than $10 with shipping, just the sort of thing to attract a young or novice telescope user into trying a product that is potentially very dangerous.

Given that the risk you are taking involves irreplaceable eyesight, this is very serious.

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Eclipse Observing Checklist

For this solar eclipse I will be in the middle of central Oregon, a long way from any stores, much less an astronomy equipment store. I will have to have everything I need on-hand, nothing forgotten, nothing overlooked.

A checklist is certainly in order!

The checklist below was compiled as much for myself as anyone who might read this posting. Actually writing the checklist out is quite useful as a personal double check. I need to consider that we will be camping for several days prior to the eclipse, that time will be spent hiking, stargazing, or simply relaxing in the forest with family.

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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.

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

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.

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The 1999 Losmandy Catalog

I have a pile of material that was donated to the observatory. While some of the gear will be used for outreach, a fair amount of the pile is not usable for this.  With JoAnne reminding me about the stack in her warehouse it is time for me to sort it out and dispose of it.  Among the pile was an entire crate of books… Astronomy textbooks, star charts, observing guides, and more.

A Driveway Telescope
The Losmandy G11 mount setup in the driveway for an evening of astrophotography

This pile of books included a full set of the classic Burnham’s Celestial Handbook, both volumes of Uranometria, and other treasures. After determining the observatory had no need for these I brought them to the last astronomy club meeting and gave them away. It was nice to see these books go to those who would appreciate them.

At the bottom of the pile was something that caught my eye, several old catalogs and manuals. These were just fun to read through. There are both Losmandy and Takahashi catalogs from 1998 and 1999, as well as a manual for a Takahashi FS Series refractor.

1999 Losmandy Catalog

The 1999 Losmandy catalog was particularly interesting. My old Losmandy G11 is a workhorse mount, one that has seen many adventures with me. The manual includes a price list, showing that it once sold for $3400, quite a bit more than the $1400 I paid for mine used in about the same era. Interestingly Losmandy still sells this mount and most of same accessories found in this catalog.

As I read I realized that this catalog may also be good to scan and post so that others may find this catalog a useful resource. I hope to scan and post some of the other items in the stack that might be good to save.

Replacing the Celestron NextStar GPS Battery

When your Celestron GPS telescope will not get GPS fix for a long time, or the GPS will not work at all, it is time to replace the battery on the GPS receiver board. Another symtom is when the telescope may get a fix, but it is incorrect, the time or location no where close.

Celestron Telescope GPS Module
The Celestron GPS telescope GPS module with the original battery
Instructions for replacing the battery are posted elsewhere about the web. There are excellent instructions for battery replacement on the NexStar Resource Site. It was those instructions I was following when I was recently replacing the battery in our ‘scope.

The GPS board is found in the main section on the oldest telescopes, but located in the arm in later ‘scopes. Our is located in the arm, a small circuit card just under the inside plastic panel connected to an antenna by a cable. Simply remove the four screws holding the plastic panel and you have access. The antenna cable can be disconnected with some gentle tugging, two screws for the board, one more connector and the board comes out. The battery is found hidden on the underside of the PCB.

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The Hotech CT Laser Collimator

With Jupiter still near opposition and Mars opposition approaching I would like to do a little high resolution planetary imaging. For planetary I use our Nexstar 11″ telescope, with 2800mm of focal length is has the high magnification needed.

SCT Alignment
Aligning our Nexstar 11″ with a Hotech CT Collimation Tool
One lesson in high resolution imaging is that collimation matters. Having the optics in your telescope precisely aligned makes all the difference in the results. A small misalignment will result in mushy images that will not quite focus properly. No amount of fancy image processing will salvage the image.

The Nexstar has not been giving me the results I know it is capable of. I shot Venus just before inferior conjunction and noted that there was probably some issues in collimation that were not addressed in the quick star collimation I had performed.

Thus I borrowed a Hotech CT Laser Collimatior from a friend. The collimator is an interesting piece of kit, enabling the user to check more than simple the tip-tilt of the secondary.

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John Dobson (1915-2014)

Today an amateur astronomy icon passed away.  John Dobson popularized the very simple design of telescope that came to bear his name, the Dobsonian.  As a Vedantan monk John possessed few material means, pursuing a passion for telescope building in the monastery garden shed he designed a telescope that could be built from whatever scrap parts he could scavenge.  He could often be found around San Fransisco showing the wonders of the night sky to anyone who would look through one of his telescopes.   His infectious enthusiasm for astronomy led him to help co-found the San Francisco Sidewalk Astronomers.

Chris Fuld using his monster 40″ dobsonian at Oregon Star Party 2013

The Dobsonian is a telescope that is characterized by an extraordinary simple and robust design. Made of plywood and other hardware store parts, there was nothing in the design that could not be built by hand.

The optical layout is a standard Newtonian design with the eyepiece at the front of the telescope.  This allows the heavy primary mirror to be located quite close to the ground.  The entire telescope rotates on a simple lazy-suzan azimuth bearing made of plywood, formica and teflon blocks.  A simple set of trunnions allows the telescope to be raised and lowered in elevation.

Dob Silhouette
Steve Dillinger’s 20″ Dob awaiting full dark at Sentinel, AZ with Venus and the Moon shining behind

The Dob brought large aperture astronomy into reach of thousands of backyard observers.  Anyone with a modicum of skill could build a Dob in a garage with simple hand tools.  Commercial designs soon appeared at very affordable prices.

Amateur telescope makers have built upon John’s ideas, creating elegant designs that far surpass those simple telescopes made from scrap. Aircraft grade plywood, machined aluminum frames, carbon fiber and computerized controls are common in modern Dobsonians. The design can be scaled up, Dobsonians are sometimes enormous, with telescopes of 30 or 40 inches aperture seen at many star parties. At OSP last year I setup next to a 40″ built by Chris Fuld, a monster telescope built by hand.

John spent much of his later life touring wherever dark skies, telescopes and people could be found. This often included national parks and regional star parties. I met John a few times across the years, at Grand Canyon Star Party and at an evening observing session at Starizona, an astronomy shop in Tucson. His signature graces the secondary cage of my 18″ f/4.5 Dobsonian, Deep Violet, beside the signature of David Levy.

John Dobson Signature
John Dobson’s signature on the secondary cage of Deep Violet

John was also a proponent of a decidedly non-standard cosmology, believing that the Big-Bang model had fatal flaws.  His alternate ideas make…  Uh?  Interesting reading.  He describes a recycling steady state cosmos heavily influenced by the teachings of eastern religions and mystical thought.

John Dobson died today, 15 January 2014 at the age of 98 in Burbank, California.  John leaves behind a son, many friends, and a community indebted by his contributions to amateur astronomy.  My friend Dean Ketelsen knew John far better than I did, I suggest you read his notes on his passing.

I spent a few moments and put all of the photos of dobsonian telescopes that have appeared here on Darker View into a gallery.  The photos are just a little sliver of what John Dobson meant to amateur astronomy…