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philwatson
member
Reged: 11/15/05
Posts: 17
Loc: Melbourne, Australia
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This scope had its genesis at an Australian star party last year, when Stephen Sharpley & I were discussing the dob trend to sub-F/4 optical systems made possible by the Paracorr, & the associated benefits of ditching ladders. Not wishing to waste a good idea, the following week we ordered a 20" F/3.7 mirror from Mark Suchting, & here we are. I did seek constructional advice from this forum along the way, so I am pleased to post photos of the finished product.
A few key details:
- It is built from 12mm hardwood ply, with a stainless steel cell
- Scope weight is 25kg (55lb), excluding rocker box
- It has a 4" secondary from Antares Optics
- There's a built-in filter slide with an NPB filter permanently mounted. The Paracorr is also permanently in the focuser
- Mirror has front collimation for ease of adjustment
- Components can be handled by one person, & it fits in a compact car.
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25cm binoscope
50cm ultralight dob
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lightfever
Pooh-Bah
Reged: 09/27/04
Posts: 1281
Loc: Macomb Michigan
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Wow! very nice looking congrats. 
That's a nice looking upper cage for an ultralight.
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Mark
Tasco 15-TE 76mm
Sky Watcher 80mm ED
AT-111 Triplet
XT8i (with Woden re-figured mirror)
Discovery 12.5" f/5 Premium DHQ (PDHQ Split-tube Dobsonian)
12.5" f/6.3 Dob (Underconstruction)
Celestron CG-5GT EQ Mount
Celestron C4 EQ Mount
"Life is not about waiting for the storm to pass, but learning to dance in the rain" unknown
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johnnyha
Pooh-Bah
Reged: 11/12/06
Posts: 1141
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What is the EP height at zenith?
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Johnny
Spicewood, TX
Sherman Oaks, CA
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philwatson
member
Reged: 11/15/05
Posts: 17
Loc: Melbourne, Australia
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Eyepiece height at zenith is currently 71", but I can shave a further 2" off it with a bit of tweaking.
I thought about a single upper ring, but went with a traditional UTA to protect that big secondary.
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25cm binoscope
50cm ultralight dob
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reiner
super member
Reged: 09/28/05
Posts: 100
Loc: Freiburg, Germany
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Hi Phil,
this is a very nice scope that you built! Is this an ultra-thin mirror (25kg is very lightweight for the complete scope)?
I completely agree with you about the traditional upper cage. Single ring UTAs have their advantages, if it comes to making a telescope air-plane-compatible. But for "daily" life, the traditional ones give better protection.
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Reiner
22" and 14" Dobs on EQ platforms
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philwatson
member
Reged: 11/15/05
Posts: 17
Loc: Melbourne, Australia
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Yes it is a very thin mirror (40mm at the edge). Much better for lifting it and also cooling, provided it is properly supported.
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Alan1956
super member
Reged: 02/07/05
Posts: 137
Loc: Albuquerque, NM, USA
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Optical tube assembly weighs 25kg? Fabulous! This includes the weight of the secondary cage and the primary mirror, I assume?
Alan
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philwatson
member
Reged: 11/15/05
Posts: 17
Loc: Melbourne, Australia
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Yes, it does include secondary cage & primary. One trick I used: that light baffling on the secondary cage is just foamboard. This is stuff you can buy at craft stores. It is 1/4" high-density foam skinned with cardboard on each side. I painted it on both sides for weatherproofing & also to make the inside matte.
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