Pulsar No 15 Winter 2007 - Astronomy in...

Winter 2007: No. 15

RASC

PULSAR T H E N E W S L E T T E R O F T H E K I T C H E N E R - W A T E R L O O C E N T R E O F T H E R O Y A L A S T R O N O M I C A L S O C I E T Y O F C A N A D A

In this Issue:

Have Scope, Will Travel Designing and building a portable telescope

Editors love theme issues. They’re usually hard to arrange but every now and then, when the stars align just right (my apologies for bor-rowing a phrase based on astrology!), your be-leaguered Pulsar editor receives more than one article on a related topic. That’s what lead to the theme of this issue: Amateur Telescope Making.

Note that the term includes the construction of any astronomical device, not just a telescope. In this case we do have an article about making a

telescope, but we also have one about construct-ing a barn-door tracker, a design that’s consider-ably more elaborate than two hinged boards.

Isn’t it nice not to have to wade through yet another article about astrophotography? As I warned way back in the reborn Pulsar’s very first issue, that’s almost all you’d see here if members didn’t send in articles. So be sure to thank the authors of the ones I just mentioned for stepping up to the plate!

K-W Centre h t t p : / / k w . r a s c . c a

R O Y A L A S T R O N O M I C A L S O C I E T Y O F C A N A D A

Find out why a club meeting was held at a roadhouse restaurant.

Bold and Beautiful Winners of the annual astrophoto contest.

- see page 6

It’s da Bomb?

Editor’s Corner

Alen Koebel, Editor

M45, the Pleiades, by Brady Johnson. A 30-minute exposure on a StarlightExpress SXV M8C 4-Megapixel, one-shot colour CCD camera through a Canon 300mm, f/2.8 lens at f/4, all mounted on an EQ6 SynScan.

Observatory Blues The Ayr observatory’s days are numbered. See why inside.

Beyond the Call Braving the bitter cold to introduce youngsters to the winter night sky.

No Quantum Soup? That Big Bang brew of fundamental particles wasn’t on the menu at the annual dinner.

Scope in a Box How to stuff a 7.5-inch scope into a box small enough for travel.

Barn-door Build-up A barn-door tracker that even Tim “The Tool Man” Taylor would love.

CES 2007 Report Yes, there were a few telescopes among all of the flat-panel displays!

Sky Walking Learn to do it with the book “A Walk through the Heavens”

PULSAR Winter 2007: No. 15

T H E N E W S L E T T E R O F T H E K I T C H E N E R - W A T E R L O O C E N T R E O F T H E R O Y A L A S T R O N O M I C A L S O C I E T Y O F C A N A D A

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Club News

Raucous Roadhouse Rendezvous

If you don’t attend the club’s monthly meetings, don’t visit the club’s web site and don’t pay attention to the back page of every Pulsar you may not know that club meetings are usually held in a lect-ure hall in the Science Building at Wilf-rid Laurier University in Waterloo. It’s a great venue with an LCD projector and amplified loudspeakers. There are two such similarly-equipped rooms, in fact. Only rarely have they been unavailable, usually during exams, and the meeting diverted to a much smaller room without A/V equipment. But at least there was still a room.

That wasn’t true of the December meeting. Your editor wasn’t there, but rumours circulated later that a bomb threat made any and all rooms unavail-able. The truth was less exciting; there were just too many exams taking place

and the club’s meeting got bumped! With no other option in sight, the

executive moved the meeting to Zeke’s Feed and Fuel Restaurant in Kitchener. That’s where many members would have ended up anyway after the meeting by long tradition for a late night snack washed down with liberal quantities of liquid barley and hops. This time they just arrived a little early.

After a long wait for the back room to become available (the only space big enough) the meeting began. However, since the back “room” is separated from the rest of the establishment only by partial walls, the din was frightful.

Despite the noise members did man-age to discuss some club business, in-cluding the status and future of the Ayr observatory (see below). On the positive side, it was the first LCBO-licensed monthly meeting in memory!

tory sits on will likely be mined to pro-vide aggregate for building the yard.

The site contains four buildings: a two-story dome, a single-story dome, a roll-off-roof structure and an outhouse. These have to be completely removed from the premises by the end of Septem-ber. Even the fence has to go.

The main complication for demolition is the main dome’s steel-bar reinforced concrete pier. However it’s done, it has to be razed to the ground along with everything else, and the site returned to its original, pre-construction state.

Even if this were not coming to pass, the consensus of club members was that the observatory was becoming too ex-pensive to operate, what with the region deciding to levy a large increase in pro-perty taxes on Mr. Dance for the club’s use of a small portion of his land.

After the demolition, which is likely to be expensive, the club has to decide what to do about an observatory for the future. Should we have one at all? If so, should it be a permanent structure again or perhaps a mobile affair built from a trailer, which could potentially be haul-ed to different sites both near and far?

Whatever the choice, it has to meet the needs of club members while also allowing the club to fulfil its RASC mandate to popularise astronomy in the local community.

Zeke’s Feed and Fuel Restaurant is a great place for having fun, but the raucous atmos-phere isn’t suitable for holding meetings!

Observatory Blues This time next year the club’s obser-

vatory near Ayr, Ontario will be just a memory. The land the observatory sits on, which the club rents from a farmer, Mr. Dance, will be sold to CP Rail by the end of 2007. CP Rail is intent on building a marshalling yard due south of the site. The small moraine the observa-

The end of an era. The venerable old lady and her consorts must go!


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An important part of fulfilling the club’s primary mandate to popularise amateur astronomy in our community is reaching out to schools to introduce children to the wonders of the night sky. Several club members donate their time and their telescopes to this cause, led by the club’s Outreach and Education Coordinator George Peer.

George approaches his job with gusto and sometimes, he goes above and be-yond the call of duty. One such occas-ion was January 25th at the YMCA Out-door Centre on Paradise Lake near St. Clements, where George was scheduled to give a talk and hold an observing session that evening for 40 children from Gateway Drive Public School in Guelph.

Unfortunately, the temperature had plummeted to –23 degrees C. The camp director had earlier in the day expressed some concern that this might be too cold for the children. Since that opened the possibility that the observing session might either be curtailed or cancelled outright, George did not invite other telescope owners out to the camp as he normally would have.

But as it turned out, the camp director underestimated the stamina of the chil-dren. It also helped that George divided the observing time into two, shorter ses-sions, with the indoor talk between them to allow the children (and the presenter!)

to warm up. And fortunately, there was no wind to make the bitter cold feel even worse.

During their time outside, the stud-ents showed a great deal of enthusiasm and didn’t seem to mind the cold at all. They became very excited when George pointed out different parts of Orion with his green laser pointer and were thrilled by close-up views of the Moon's craters through the telescope he brought.

All in all, a successful and rewarding evening despite the frigid temperatures.

Illustrations in the book show multi-ple pathways between groups of con-stellations to explain their associations to one another in the sky. Other dia-grams show how to find naked-eye star clusters (e.g.. the Pleiades), galaxies (e.g., the Andromeda Galaxy), and notable double stars. In one section of the book the legends of the constella-tions are told in a very positive manner suitable for young children. I found the stories both enlightening and uplifting.

Four seasonal constellation charts are included, with the cardinal points mark-ed on their circumference for orienta-tion to the horizon. The book’s light weight works in its favour here, allow-ing even young children to easily hold it up to compare the maps and diagrams directly to what they see in the sky.

Although the book seems to be aimed at youngsters, it should prove valuable to novice stargazers of any age. It will even help experienced amateurs who have forgotten their way around the sky, usually because they’ve become too reliant on a GoTo device.

This is a "must have" book for all novice stargazers and I recommend it to anyone who wants to improve their ability to "walk through the heavens."

Above and Beyond

Club News

Book Review

[Milton D. Heifetz and Wil Tirion, 72 pages, Cambridge University Press, 2004, 3rd edition, ISBN: 0521544157]

For most novice stargazers, finding constellations in the night sky can be difficult. Star patterns that seem obvi-ous on paper can be difficult to find in a sky filled with thousands of stars of differing brightness’s. In addition, the rotation of the sky as the earth turns can present constellations at strange angles.

This book presents a method to make learning the constellations easy. It is based on using an outstretched hand and fingers to measure angular distances between a constellation's stars and be-tween neighbouring constellations.

Starting with the easily recognised Big Dipper, the system uses two con-necting stars in each constellation to point to a neighbouring constellation, thus allowing navigation between all the major constellations in the Northern sky. (The Southern sky is not covered.)

A Walk through the Heavens: A Guide to Stars and Constellations and their Legends by Duncan Class



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Travel

were even more goodies than last year, if that’s possible. Let’s all thank the individuals and companies (some of them one and the same!) who donated to the cause. Their generosity is greatly appreciated.

If you didn’t go, you missed a great time. Let’s see everyone out next year!

Last year the club’s annual dinner moved to March from the traditional January because of easier room booking and better weather. The event this year was on March 3rd.

Well, March usually has better weath-er. This year was an exception. “In like a lion, out like a lamb,” they say. The lion made an appearance in the form of snow and some freezing rain. But it could have been worse; just two days prior a major close-all-the-schools snow storm passed through.

A little bad weather, however, didn’t keep club members and guests from attending. Fifty five of them made it out to the Royal Room at Golf’s Steak House and Seafood Restaurant in Kit-chener, up slightly from last year.

A happier bunch you couldn’t find. Golf’s tasty buffet no doubt contributed to this (and no lamb or lion anywhere in sight!). But it was co-organizers Kate Baker and Roseanna Rigo who really made the night a success. They worked hard both before and after the event to ensure that everything went smoothly and that everyone had a great time.

Club president Dave Garner was mas-ter of ceremonies this year. After dinner, your hard-working editor presented the

awards for the winners of the astrophoto contest (see the winning photos on the next page). He (me!) followed that with a seven minute slideshow set to music that showcased club activities and note-worthy member astrophotos from the previous four years.

After enough Mars Bars to make a dentist smile were awarded to the table who best solved a lunar-themed cross-word puzzle, Kate and Roseanna raffled off the door prizes. It seemed like there

Club News

Lion, not Lamb, Featured at this Year’s Club Dinner


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Club News

Fourth Annual Astrophoto Contest Winners

There were 31 entries from eight members this year, more than enough for a healthy competit-ion. Just over half of the entries were submitted to the Deep Sky category. The quality of the photos was extremely high; it looks like everyone is getting the hang of their digital SLR and CCD cameras (few of the submissions were taken with film and none of those won). Voting took place at the club’s February meeting.

Winners in each category received a $50 prize at the annual dinner. The photo with the highest num-ber of votes was crowned “Favour-ite Astrophoto,” and that winner received an addi-tional $50. Who said all that hard work under the stars wouldn’t pay off?

Deep Sky: NGC891, by Ronald Brecher

Special Event and Favourite Astrophoto: Comet Swan, by Darryl Archer

Fixed Tripod: Earthshine, by Sergio Mammoliti

Constellation Portraits: Brocchi’s Cluster, by Peter Clarke

L,P & S: Moon, by Brian Hollander



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Who says all the action at a star party takes place at night? It’s dur-ing the day-time hours while one waits for darkness, that social act-ivities abound and ideas get floated. It was at one such gathering, the 2004 Huronia Star Party, that a brain-storming session about build-ing the “perfect portable telescope” arose.

Alan Ward and myself were ad-miring all the large telescopes that peppered the field while at the same time lamenting that even 8-inch or 10-inch ‘scopes took up lots of room in a car, room that might otherwise be used for camping gear and/or astronomy accessories.

Similarly, we wondered why even at those modest apertures it often takes two or three trips to carry all the com-ponents from the car to your observing location. There had to be a better way!

A Plan takes Shape Right then and there we resolved to

build a portable Dobsonian telescope of reasonable aperture that would package up “within itself,” take up little space, be readily transportable in one trip by one person and be quick to set up. As the discussion progressed into the night, we outlined the broad strokes of the project and committed ourselves to its execution. We decided that we would jointly work out a design, Alan would provide the optics and I would do the actual construction and assembly.

Right from the start we had a decided

advantage. A neighbour of mine worked for a kitchen cabinet company, a local firm that had the one crucial piece of equipment we would need to pull this off: a CNC router. This amazing mach-ine could upload AutoCAD drawing files and cut all the pieces from a full sheet of plywood; all in one shot and all at extreme precision.

As the summer turned to fall and fall into winter, we searched the web for unique designs. Ultimately we found a very cool eight-inch “Briefcase Tele-scope” built by a guy by the name of Peter Pekurar in (of all places!) Kitchen-er, Ontario, whom Alan had met once before. However, while we would have liked to ask for detailed drawings we didn’t want him to feel pressured, nor did we want to steal his idea outright. So we kept looking.

During my research, one web site in

particular caught my eye. A Ger-man fellow named Gerd Huissel had built an interesting ‘scope that appeared to incorporate everything we wanted. His web-site (www.bksterngucker.de/_en/ atm/gehutrvldob.htm) invites others to copy all or part of his design. I emailed him for more information, but when I did not receive a reply after a few weeks I decided to “wing it” with what I could see on his web site.

Detailed Design We decided on the size of the

telescope when Alan got a hold of three 7.5-inch mirror blanks and started grinding. We wanted to keep the weight down and the ‘scope short, so a focal length of 1,000mm (f/5.2) was chosen. With that key piece of informat-ion, I roughed out the critical dimensions and over the Christmas holidays the drawing

effort took on a life of its own. Within two weeks we had a final detailed version (Figure 2) with the following features:

• A 6-pole truss design using ¾-inch (0.060-inch wall) aluminum tubing, each pole a stiff two-piece assembly using threaded inserts for quick set-up and takedown.

• A comfortable eyepiece height of 28 inches above ground when pointed at the horizon, and almost 56 inches when pointed at the zenith, achieved by converting the box lid into an elevated stand for the rocker box.

• Balanced for a ¾ lbs. eyepiece and a Rigel finder, with small counterweights to be added for heavier eyepieces

• The entire instrument closes up into a sealed box using only its own compon-ents, with even the disassembled two-piece truss tubes inside.

Designing and Building a Travel Scope

by Mike Renner

Feature

Figure 1. The 7.5-inch travel scope. All photos by the author.

http://www.bksterngucker.de/_en/atm/gehutrvldob.htm

http://www.bksterngucker.de/_en/atm/gehutrvldob.htm


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• A finished size when packaged up of 12-1/2 inches x 12-9/16 inches x 16-3/8 inches high.

• A total weight of 32 lbs.

The Team Grows

With everything else in place, we still had one big problem. The project called for specialized hardware: truss tube clamps & threaded connectors, mirror mount bits, secondary spiders, focusers, etc. Who would do the machining? Where would we get these parts?

It struck me that I knew just the right guy: Andy Niscior, from Toledo Ohio. I had met Andy online the year before when we battled over a 10-inch mirror on eBay. I won that auction, but Andy proudly contacted me a week or so later to tell me he got the next 10-inch mirror for $15 less than I paid.

We became good friends and shared ideas while building our scopes. Andy is a skilled die-cast mould maker who worked for a GM transmission plant at the time. He was a natural choice for our

team and we invited him to join us. He loved the idea and quickly accepted. At this point we had all the skills we needed and a functional design. It was time to build!

Building the Scopes

Cutting the wood for all three scopes was relatively easy. I simply handed the AutoCAD file and some drawings to my neighbour and patiently waited while he sourced the Baltic Birch plywood (3/8-inch and 3/4-inch thickness) and did the cutting. As his shop was quite busy, it took almost six weeks to finish the job. By then, Alan was well underway with the mirrors and Andy was busy making the mechanical bits and pieces.

When the cut pieces of wood arrived (they were beautiful) everything fit to-gether precisely (Figure 3). All straight cuts were on-size and square and all circular cuts (altitude bearings, second-ary cage rings and mirror mount plates)

looked like they had been machined to perfection. You just cannot duplicate this accuracy with traditional wood-working tools!

There was an added and unexpected bonus to this method. Since I didn’t have to cut plywood sheets in my base-ment, there was very little sawdust gen-erated in the house and it was easy to keep my workshop clean.

Assembly was often tedious and time consuming but everything went together well, a process that took about two months. During that time, a steady stream of parts was coming in from Andy. I was amazed at the helical focus-ers he built, likewise the truss tube clamps – they fit like a glove. He took basic dimensions from my AutoCAD drawings and turned it all into a 3D model. He fed that data into a CNC mill and voila – three full sets of custom de-signed truss tube clamps.

The secondary cages took the most

RASC

Figure 3. CNC-routed wood pieces in the process of being assembled.

Figure 2. The detailed design in AUTOCAD.



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time to assemble since many small wooden parts, the focuser, three truss tube clamps and the secondary spider all had to be intricately located and fit-ted. The final result was very satisfying (Figure 4). Its light weight allowed us to balance the scope yet still allowed for the Rigel finder and a moderate size eyepiece.

The mirror-box/cell assembly secure-ly holds the mirror in place and protects it with a well fitted lid (Figure 5). We had to play with the altitude bearings to properly locate them for overall balance and when done, they were screwed and glued permanently into place.

Wilsonart® Ebony Star laminate and virgin Teflon® were used for all bear-ings; the resulting motions were super- smooth. I heartily recommend this com-bination to anyone building a Dob.

When all main components were fin-ished, it was time to build one complete scope and see how everything would go together. Thanks to that CNC router and the accuracy of its cuts, the fit was out-standing! Andy’s truss tube connectors were bang-on the correct angle and in no time at all I was looking at one really cool scope!

After spending some time admiring my new “toy,” it was time to take it apart and see if everything would pack in the box. It took a few minutes to

figure out how to orient the components, but soon I had everything stowed snugly inside (Figure 6) and the top tightly latched (Figure 7).

I quickly built up the other two tele-scopes. Now it was time to install the optics. The three primary mirrors arriv-ed in the nick of time from Alan. Each was within 5mm of the target 1,000mm focal length and measured better than 1/8-wave accuracy.

I attached the mirrors to their ply-wood mirror cells with RTV silicone and left them to set overnight. Silicone was also used to mount the Protostar secondary mirrors and they too were left to set.

Star Testing

The next day, the forecast called for clear skies so I hurriedly set about getting one of the ‘scopes ready for star testing. The adhesive had done its job so I carefully set the mirror into the mirror box, added the adjustment nuts on the back and gave the springs a little ten-sion. After I installed the secondary I could start the collimation. Looking through the focuser, I realized I had

Figure 4. The secondary cage assembly with its helical focuser.

Figure 5. The mirror box and lid. Figure 6. Everything fits inside!


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lucked out as collimation was extremely close. A few tweaks and I was there.

That night in my yard, I saw textbook pin-pricks of starlight, massive moun-tains on the moon and the divisions in the rings of Saturn. The movement of the ‘scope was buttery smooth with absolutely no backlash. Optically and mechanically, the scope was a top per-former!

I emailed my partners the good news and could sense their excitement, but there was another problem – the spring observing season was only a few weeks away and the scopes were still bare

wood; they hadn’t been finished. With three scopes to urethane, there were many hours ahead of brushing, sanding and letting the parts dry between coats; I had to start immediately! Fortunately, by working on them early mornings and evenings, the job was finished in only two weeks. The final finish had a high polish and a very smooth, almost furniture-like feel.

The ‘scopes were finished in April of 2005. Alan made the pilgrimage from Sudbury to pick up his while my wife & I drove to Toledo to deliver Andy’s scope, which was our first face-to-face meeting. All three scopes have lived up to expectations and see regular use. When my wife and I set up ours, wheth-er at a star party or a friend’s house, it seems to be the centre of attention.

EPILOG: Shortly after receiving his telescope, Andy noted an optical flaw in the main mirror. Upon close examinat-ion he found a fracture inside the glass, a defect none of us had noticed before and that had likely occurred from an internal strain after receiving the mirror. Alan promised to replace it but as “luck” would have it, his optical shop burned down! Andy found a way to mask the flaw so he could use the scope

and is patiently awaiting its replace-ment. Alan is slowly rebuilding his operation and has Andy’s replacement mirror on his priority list.

Building on Success Don’t think this is the end of Travel

Scope design for us! The saga continues as we add two new team members, up-size the design to a 10-inch model, build five copies and hit the star parties. But that’ll have to wait for a follow-up article in a future issue of the Pulsar.

Figure 7. All closed up and ready to travel.

Figure 8. Closed and open configurations.

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I have always wanted to do astro-photography but my initial foray into amateur astronomy 36 years ago didn’t give me much hope. The pillar mount I built then for a 108mm (4-1/4 inch) Newtonian reflector weighed a ton but twitched intolerably. It also lacked set-ting circles, slow-motion controls and a motor drive. It wasn’t even usable for observing, much less astrophotography!

Unfortunately, my terrible experience with that mount undermined my interest in astronomy, so the scope and the mount gathered dust (and rust) for thirty years.

Recently, my interest in astronomy was reborn. Rather than spend my kids’ inheritance on the latest and greatest from the local astronomy store before having a clear idea of what I wanted and needed, I decided to spend a while learning, observing and assessing all the

new hardware. Meanwhile, I would up-grade the pillar mount with the help of a mini-lathe I bought for just that purpose.

During this retraining period I stum-bled upon the barn-door concept. In its original form as devised by George Haig of Scotland, a barn-door tracker is simp-ly two hinged boards being pushed apart by a threaded rod turned by hand. (Haig later added a 1-rpm synchronous AC motor.) Cheap, and it works to guide a camera with a wide-angle or “normal” lens for short to moderate exposures.

Later, others started elaborating on the concept. A key thrust to their refine-ments was to improve the tracking accuracy over longer exposures. Some enthusiasts added stepper motor drives with time-varying step rates, some used a curved bolt. (See the sidebar. - Ed)

Others, like Dave Trott, used more complicated geometries with multiple hinged boards. The Trott concept in par-ticular, with its phenomenal tracking accuracy, seemed like a great interim solution, allowing me to start taking photos before the pillar-mount upgrade or a new scope were in hand.

But what kind of camera would I use? I eliminated film as an option when I saw the superior results people were getting from digital-SLR cameras and

CCD imagers. So my 35mm SLR stayed in the closet.

However, my point-and-shoot digital camera wasn’t suitable for astrophoto-graphy (no time exposure capability), so a Meade LPI seemed a good, inexpen-sive place to start. The SBIG CCD cam-era could come later, when my ship came in.

I already had several good Miranda and Olympus camera lenses, up to a 450mm f/8. All I would need to use them with the LPI was a couple of bayo-net adapters, which I could make with my mini-lathe.

Since I have been a woodworker all my life, the mechanical construction of a barn-door mount seemed like it would be no challenge. And, my formal train-ing had been in electronics. Even given that the training was many years ago, and now outdated, the motor drive didn’t seem like it would be a difficult task, either. Plus, I could use the same electronics design to make a drive for my reflector’s (improved) pillar mount.

Oblivious to the difficulties in what

Equipment

An Elaborate Barn-door Tracker Part I: Design & Construction

by Wayne Joslin

Figure 1. Side view of the barn-door tracker, showing the three boards and the drive. Boards #2 and #3 are U-shaped and interlocked so that #3 rides on #2.

Figure 2. South side of the finished tracker. A camera lens and LPI are top left, polar scope is top right, and the electronics below.


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lay ahead, I charged into the program with enthusiasm.

Design I could not find detailed plans for a

good barn-door tracker on the Internet, but there was a lot of information in bits and pieces. The web sites that I found most useful are listed at the end of this article.

Armed with this input I chose to build, not a nice simple version, but a Type 4 Double-Arm drive, which is the-oretically capable of tracking to within one arc-second for two hours!

Double-arm drives use three, rather than two, boards to do the required geo-metry correction. The motor, hung on the first (bottom) board, drives the sec-ond board. The third board, on which the camera is mounted, slides along the second. The distances from the hinges to the drive points are critical.

Construction

The tracker is shown schematically in Figure 1 and the completed unit in Fig-ure 2. A camera is attached to board #3 via a ball mount, which can be located anywhere along the board. The camera/ lens size, RA position and willingness to be stuck in the eye by 1/4-20 threaded rod affect the choice of posit-ion. I drilled three locating holes along the board to allow a choice of positions and those have proven adequate so far. A finder is mounted on the upper part of board #3 for polar alignment.

The motor and threaded rod must pivot relative to boards #1 and #2. To maintain the precise geometry that accurate tracking demands, the pivot points and the two hinges must be locat-ed on the same plane.

I was lucky to find some 3/4-inch Baltic birch plywood with a heavy mela-mine coating (almost 1/16 inch thick!). It’s black and when edged with black

iron-on, looks good, but more import-antly the melamine forms part of the sliding surface. The sliding point on board #3 is a piece of black UHMW plastic which is replaceable should it wear. I cut patterns from 1/4-inch MDF and routed the pieces to shape. There is an adjustment device added to board #3’s hinge point on board #1, for fine tuning dimensions. So far this has proven an unnecessary complication.

This assembly sits on a latitude wedge

which is adjustable from about 40° to 46°, which should serve from Port Dover to North Bay. Inside the wedge is a bubble level lit by two red LEDs and the whole shebang sits on a video tripod.

Drive

The 12-volt stepping motor came from the attic. I purchased an inexpen-sive variable speed stepper driver circuit in kit form and, using a 12V gel cell, got things turning. Under load, however, the secret smoke escaped from the driver chip and it no longer worked. I decided to add high-power Darlington drivers to make sure the electronics could take the strain. This booster is mounted on the bottom of board #1 and is visible in Figure 3.

I found another stepper motor in the attic, of the same size but five volts. I may use this to drive the pillar mount, so I added 5V capability to the circuit.

Having a variable speed drive is nice for fiddling, but two-hour tracking re-quires a constancy that it can’t deliver, and you can’t tell how fast it’s turning. To solve the first problem I added a stable, crystal-controlled pulse generator adapted from one of the Internet articles.

Figure 3. View from the North.

Figure 4. Block diagram of the electronics.



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If you’re not particularly good at woodworking, you might find this unusual tracker design attractive.

Like the simple Scotch mount, it uses two hinged boards. But instead of a straight bolt pushing against the upper board, this design uses a curved bolt attached to the upper board. In this case it is the nut that must turn, not the bolt.

Bending the bolt (actually a thread-ed rod) into a curve at a specific radius and devising a means to turn the nut are the only challenges. My solution to the latter was to glue the nut to a gear, which is turned by an identical gear attached to the shaft of a 1-rpm DC motor.

The curved rod acts like a sector of a large worm gear, so in theory the rate of separation of the boards, and thus the tracking, remains constant over the length of the exposure.

However, construction inaccuracies introduce some random and periodic errors that limit the focal length of the lens to 135mm or less. Exposures up to about 20 minutes are possible, limit-ed by the length of the threaded rod.

revolution, then repeats. By now the electronic package was

getting sizable and I was concerned with battery draw. So I redesigned the whole lot using CMOS chips because of their lower current requirements. The juice-hungry LEDs in the counter are switch-ed so they’re only used when needed.

The threaded rod is 1/4-20 and the tracker is scaled for 1 rpm. The stepper drives through a 30:1 worm gear reducer and the motor is 1.8° per step, meaning it needs 6000 pulses per minute (200 x 30) or 100Hz to generate the required one rpm on the drive rod. The gear box on the stepper comprises two pieces of 3/4-inch brass square bar drilled and reamed for the drill rod shaft. The disk cover fastens to the bottom bar and two brass plates are soldered into the top bar. At the top of these plates 1/8-inch drill rod connects to the suspension bearings which are let into board #1.

Similar bearings let into board #2 connect to a Lee Valley 1/4-20 speed nut. By twisting the nut off-axis slightly, the threads release and the mount can be reset without having to rewind via the motor. A music wire spring prevents the nut from disengaging on its own.

Results

The whole package worked with minimal shakedown – nothing short of a miracle, really, considering my inexper-ience. I took the completed gear on vacation to dark skies (Deep River, Ontario). The skies sure were dark; they clouded over all week!

In Part II of this article I’ll discuss the trials of actually getting a photo.

A switch selects between constant or variable speeds.

But how fast is it turning in the vari-able speed mode? I found no one using RPM counters on their barn-door track-ers. I would have to design something myself. It occurred to me that with a crystal oscillator now on board, I could divide down its frequency using ripple counters to ten counts per second as a reference.

So I mounted a disk on the outboard end of the drive rod and added two photo-interrupters to watch a single fine slot on the disk. Using a few logic chips, this turns a 4-digit counter on and off so that the LED readout gives the time taken to make one revolution to a tenth of a second. It resets, counts one revo-lution, holds that answer during the next

Internet Resources for Barn-door Trackers • Build a Barn Door Tracker (www.astronomyboy.com/barndoor/index.shtml) • A Better Barn Door (www.astunit.com/tonkinsastro/atm/projects/scotch.htm) • A Quartz Controlled Scotch Mount (www.mikeoates.org/mas/projects/scotch/) • The Double-arm Barn-door Drive (hometown.aol.com/davetrott/page17.htm) • How to build a double-arm barn door tracker (education.jlab.org/tracker/)

Figure 5. The stepper motor and gearbox.

A Curved-bolt Tracker by Alen Koebel

http://www.astronomyboy.com/barndoor/index.shtml

http://www.astunit.com/tonkinsastro/atm/projects/scotch.htm

http://www.mikeoates.org/mas/projects/scotch/

http://hometown.aol.com/davetrott/page17.htm

http://education.jlab.org/tracker/


Winter 2007: No. 15

13

RASC

to see are “personality” modules. The Einstein personality, for instance: “You are pointing at the location of Cygnus X-1, the first black hole ever discovered. May I remind you that God does not play dice with the Universe?”

I ask about the fate of Celestron’s 20-inch C20 Dall-Kirkham, which proudly occupied a two page spread in last year’s catalogue. The answer confirms the rumours I heard before the show; Celestron will not be producing it after all. But I also hear something new; that a employee with a side business making high-end ‘scopes will manufacture and sell it instead. Why? It’s not a good fit for the “new” Synta-owned Celestron, whose corporate mission is now appar-ently to make astronomy accessible to everyone (hence the SkyScout). That’s admirable, but b–o–r–i–n–g. So move along folks, there’s nothing to see here.

Thursday, January 11: Today I’ve returned to the LVCC. It’s in this build-ing’s Central Hall that most of the giants of consumer electronics are exhibiting: Names like Canon, LG, Panasonic, Samsung, Sharp, Sony and Toshiba, to name only a few. I find Meade’s booth way at the back of the hall. While it’s about twice the size of Celestron’s, it’s tiny compared to most others here.

since it started shipping in July and that the company expects to sell twice as many in 2007. Gee, that seems like a safe prediction since that will be just over twice as a long a sales period!

Celestron is making good, if a little slowly, on the promise it made at last year’s CES to provide tours of the sky on SD memory cards for the SkyScout, imaginatively called SkyTours™. Its first two, which should be available this summer, are “Astronomy for Beginners” and “The Sky Explorer”. What I’d like

Wednesday, January 10: I’m in the Sands Expo and Convention Center in Las Vegas, here again to walk the end-less aisles of the International Consumer Electronics Show (CES). I do it every year as a Contributing Editor for Wide-screen Review, a well-regarded home- theatre print magazine.

The main halls of the show are act-ually several Vegas-sized blocks away in the Las Vegas Convention Center (LVCC), but I’ve made the trek to the Sands this day to check out Celestron’s booth, among others. With so many car-peted aisles criss-crossing the huge hall between the exhibitors, I feel like a mouse in a maze. With the aid of a map, I finally find the booth.

Last year the company introduced the SkyScout,™ a zero-power, GPS-equip-ped “personal planetarium,” to great acclaim, winning two prestigious “best of” awards at the show (see Issue 11). What amazing innovations will I find this year?

A quick scan of the booth is disap-pointing. The only obvious new product is the VistaPix™ IS70 Imaging Spotter, a 70mm spotting ‘scope with a built-in 3.1-megapixel digital camera and 2-inch LCD flip screen. I have to admit it looks nicely designed and it’s certainly a boon for bird-watchers; no more juggling of binoculars and camera. The price is even reasonable: $480 US. But it’s not of any use for astronomy.

I also see an assortment of small GoTo ‘scopes, but they’re all variations on a familiar theme. I ask a Celestron representative about the SkyScout. She tells me that sales have been “huge”

CES 2007: Star Biz

Show Report

by Alen Koebel

Meade’s new MAX mount and 20” RC ‘scope.

The flat-panel display here is just for advertising, but these things were everywhere at the show!

OTA attached to it. While you can buy the mount alone for $20,000 US, it’s normally sold with either a 16-inch RC for $30,000 or the 20-inch for $40,000. Clearly, unlike its competit-ion over at the Sands, Meade isn’t afraid to tackle the high end.

Wiping the drool from my mouth, I ask a Meade representative about the controversy surrounding the use of “Advanced Ritchey-Chrétien” to name their optical design, consid-ering it uses a corrector-lens-and-spherical-primary-mirror combination in place of a true RC’s hyperbolic primary (both designs use a hyperbolic secondary).

His answer: First, Meade has never made a secret of the fact that it uses a corrector plate and who says an “advanced” Ritchey-Chrétien can’t have one? And second, who really cares what it’s called? The important thing is: Does it work? Judging by the reviews (I’ve never looked through one myself), I would have to say that it does!

The sales representative then tells me that both the mount in the booth and the 20-inch ‘scope perched on it are for sale at a deep dis-count. They’d prefer, apparently, not to have to ship the combo, which weighs nearly 700 lbs., back to California.

I’m not sure if he’s serious but for, oh, about a millisecond I entertain the idea. Lucky for me, better sense prevails and I walk away, my savings safe for more responsible uses like buying groceries and paying the mortgage. Some things will just have to stay, as they say, in Vegas.


K-W RASC Executive President: Dave Garner Past President: Mike Burns 1st Vice: Paul Schumacher 2nd Vice: Brian Hollander Secretary: Phil Lacasse Treasurer: Peter Clarke

The K-W Centre of the Royal Astronomical Society of Canada usually meets on the second Friday of every month excluding July and August. Meetings are held in the Science Building at Wilfrid Laurier University in Waterloo, Ontario. All residents of the Milky Way are welcome but must supply their own transportation.

PULSAR Staff Editor: Alen Koebel Assistant Editor: Jeff Collinson Layout Design: Brady Johnson

Other Editorial Contributors: Darryl Archer, Kate Baker, Doug Bates, Doug Bulgin, Ralph Chou, Peter Clarke, Duncan Class, Jim Failes, Brian Hollander, Wayne Joslin, John Kulczycki, Phil Lacasse, Bernd Mueller, George Peer, Peter Pekurar, Brenda Purdy, Mike Renner, Brent Spencer, Tim Spiegel-berg, George Tomesch, Maryanne Weiler

2007 Kitchener-Waterloo Centre of the Royal Astronomical Society of Canada. All rights reserved.

RASC K-W Centre h t t p : / / k w . r a s c . c a

R O Y A L A S T R O N O M I C A L S O C I E T Y O F C A N A D A

Want to join our club? To become a member please

call Peter Clarke at 519-763-0184 or send e-mail to

[email protected]

In Coming Issues… Observatory Retrospective How to cure Telescope Addiction World’s lightest 25-inch Dobsonian?

and lots more…

But as I walk up to the booth it’s already making a good impression because there, front and center, is Meade’s swanky new product for 2007: the MAX mount. Boy, this thing is big! Meade claims it’s “built like a tank crafted by Swiss watchmakers” and it sure looks it. The company recommends a maximum payload (excluding counterweights) of 250 pounds. That seems like a conservative figure based on what I see before me.

Here in the booth the MAX has an equally impressive 20-inch Advanced Ritchey-Chrétien

CES 2007: Star Biz continued…

Close-up of Meade’s massive MAX mount.

Pulsar No 15 Winter 2007 - Astronomy in...

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