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Commissioning a large scope for visual use

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#1 Edd Weninger

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Posted 20 May 2014 - 10:59 PM

As I approached full retirement, my wife and I were thinking where to retire to. Our thoughts were – anywhere but California and someplace with a lifestyle change. We both enjoyed visits to Flagstaff AZ and the area became our first targeted area. We intended to keep our SoCal house, purchase in the Flagstaff area and establish residency there. It was important that we be able to commute with a brief flight from Long Beach CA. Flagstaff has a nice airport and would be ~2 hour’s flight time. My main passion was/is aviation. I’ve been a pilot all my life and flew for business and pleasure.

Astronomy is another interest and somewhere in our thinking was that we would build an observatory. At 15 I started to grind an 8” mirror from an Edmunds kit. Everyone said to start with a 6” and they were right. I had an orange tube C-8 seemingly forever using it in the back yard and at a cabin in Big Bear on a very casual basis.

#2 Edd Weninger

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Posted 20 May 2014 - 11:02 PM

I had built a small observatory at our SoCal house and equipped it with a NexStar 11 GPS for visual. I anticipated doing astro-imaging when retirement was real, and gathered gear to do this.

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#3 Edd Weninger

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Posted 20 May 2014 - 11:03 PM

Things took a sudden turn when I accidently learned of a private airpark in central Arizona. As a homeowner you were permitted use of the runways and taxiways and to have a hangar for your plane right next to your house. We looked at several properties and bought one we love. When looking at the property I noticed a utility shed I thought might be converted to an observatory, but it was only a passing thought.

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#4 Edd Weninger

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Posted 20 May 2014 - 11:04 PM

Our aviation requirements met, and our lifestyle here is better than ever.

So when things settled down from the move, et al, I began to think about astronomy activities. I learned of BYO and was fortunate to have them visit and convert the shed to a ROR observatory.

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#5 Edd Weninger

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Posted 20 May 2014 - 11:07 PM

Poking around the web about a Meade 16” SC provided mixed reviews. In my mind, too many issues for the small numbers in use. One particular comprehensive review painted a picture of frustration rather than reward for one user. He needed to de-fork it to resolve mount issues. When GEM mounted, there were unsolved issues with the OTA. All this over a 2 year period. He went to a custom built 16” Mak-Cass.

I didn’t need 2 years frustration, so I followed his path. I have a Questar 3.5” which has always impressed me with its performance for its size, solid collimation and good optics.

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#6 Edd Weninger

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Posted 20 May 2014 - 11:08 PM

The custom build would take a while, but I had enough equipment to enjoy the sky.

After some preliminary discussion with Markus of APM – Germany, we entered into a contract to build my scope. Intes-Micro would make the optics. Markus would have interferometry testing done and subsequent coatings. Matthias Wirth would make the mechanical bits, do the assembly, collimation and star testing. I provided certain specifications with regard to focuser, back focus, mounting method and accessory mountings, etc.

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  • 6537427-060 Mak 16 dwg.jpg


#7 Edd Weninger

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Posted 20 May 2014 - 11:10 PM

I was kept apprised of the progress of the build without my prompting.

The mechanical bits were done faster than the optics, and awaited final fitting with the optics.

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  • 6537429-070 Mak metal.jpg


#8 Edd Weninger

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Posted 20 May 2014 - 11:11 PM

The tube design is unusual in that the 16” optics are installed in a 20” tube. This leaves 2” of clearance per side for the purpose of keeping tube currents away from the entrance light cone. This also allows the mount rings to be internal. This picture is not my scope, but shows the internal rings well.

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  • 6537433-075 APM Mak-front.jpg

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#9 Edd Weninger

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Posted 20 May 2014 - 11:13 PM

When the optics were delivered to Germany, Matthias confirmed dimensions and adjusted the metal if/where needed. Beginning to see the parts come together increased anticipation of receiving the completed scope. This is Matthias measuring the meniscus.

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  • 6537435-080 Matthias meniscus.jpg

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#10 Edd Weninger

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Posted 20 May 2014 - 11:14 PM

Here is Matthias checking the primary mirror.

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  • 6537437-090 Matthias primary.jpg

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#11 Edd Weninger

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Posted 20 May 2014 - 11:16 PM

Here is the secondary. This Mak-Cass is built in a RuMak configuration. The Ru recognizes Harrie G. J. Rutten as the designer if this derivation of the Mak-Cass design. The secondary is a separate optic, which gives a designer another degree-of-freedom to optimize the design.

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  • 6537438-100 Secondary.jpg


#12 Edd Weninger

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Posted 20 May 2014 - 11:17 PM

This is the back of the primary mirror, polished for thermal characteristics. It is an amber color because it is Astrosital, a glass formulated for low susceptibility to temperature changes.

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  • 6537441-110 Mirror back.jpg

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#13 Edd Weninger

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Posted 20 May 2014 - 11:18 PM

Matthias doing the final assembly.

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  • 6537444-120 Matthias assembling.jpg

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#14 Edd Weninger

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Posted 20 May 2014 - 11:19 PM

Fitting the meniscus in its cell.

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  • 6537446-130 Matthias fitting meniscus.jpg

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#15 Edd Weninger

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Posted 20 May 2014 - 11:20 PM

Near done.

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#16 Edd Weninger

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Posted 20 May 2014 - 11:22 PM

This picture shows the rear of the scope well. There are three fans to provide for cool-down when needed. The fans blow in and the air escapes via vent holes just behind the meniscus.

The focuser is a 3 ½” Starlight Feather Touch, located at the right place and with enough throw to accommodate a Baader Mk-V binoviewer without the extending lens, and a 2” A-P Maxbright diagonal.



There are 2 electrical plugs for the fans and for an anti-dew heater for the meniscus, wired internally.

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  • 6537454-145 rear assembled.jpg

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#17 Edd Weninger

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Posted 20 May 2014 - 11:24 PM

Final touches.

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#18 Edd Weninger

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Posted 20 May 2014 - 11:25 PM

Markus would have provided the overseas delivery and the necessary paperwork. However, I have a friend in the export/import business, and as an experienced broker, knew exactly what was needed, I had him arrange to pick up the crate directly from APM, arrange for air shipping by the best way, handle customs on entry and arrange custom delivery to me. I was continually apprised of the progress throughout the journey.

This is crate as it arrived. Note the customs tape was intact, meaning my broker was trusted enough, via his paperwork, that customs did not need to inspect the goods.

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#19 cl300stick

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Posted 20 May 2014 - 11:26 PM

Wow! What a great journey!

#20 Edd Weninger

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Posted 20 May 2014 - 11:26 PM

It didn’t take me long to open the crate.

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#21 Edd Weninger

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Posted 20 May 2014 - 11:31 PM

And get my first look at the glass – perfect !!

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#22 Edd Weninger

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Posted 20 May 2014 - 11:32 PM

I got a few friends together to mount it in the observatory. Looks like we’re moving a water heater.

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#23 Edd Weninger

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Posted 20 May 2014 - 11:34 PM

Here we are mounting the plate to the declination axis of the A-P 1200. The scope weighs 114 lbs with a 2”diagonal and 22mm Nagler. We determined the balance point of the OTA by balancing it on angle iron. When we knew that, I drilled the A-P mounting hole requirements in the plate where needed.

We mounted the plate to the mount first because 6 screws were needed with little access. Only 4 bolts are needed to mount the scope to the plate from below, using the radius blocks bolted to the internal rings.

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  • 6537474-200 Mounting plate.jpg

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#24 Edd Weninger

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Posted 20 May 2014 - 11:35 PM

OK, ready to lift. Sorry no hands to operate a camera.

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#25 Edd Weninger

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Posted 20 May 2014 - 11:36 PM

Here, the scope is in the A-P Park 1 position while we verify we got the dec axis bolt pattern in the right place. And also verify my calculations with regard to the counterweights needed. I had made a counterweight shaft extension to hold 50 lbs on a longer moment, and left some adjustment using a single moving weight. Everything came out as planned.

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  • 6537478-210 Park position.jpg

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