A Premium ATM 10" Newtonian Project

[ariefm71]

This project started when Carl Zambuto agreed to sell me his 10" f/5 Teleport mirror (the fact that he gave me a "reference" mirror was a nice surprise). The design phase took several months, the waiting for the parts took another few months since most are custom-made. This is not a pure ATM project as what I did was designing the scope, sent the design to premium component/parts makers, and assemble the scope. So, let's start with the design.

Design Objectives:
- Minimum of 10" quality aperture
- Must be able to be EQ-mounted on my Takahashi EM-100 mount (30lbs loading capacity) for imaging purpose
- Must be able to be mounted on Astroslew mount for grab and go
- Should not take more than one-person seating on the backseat of a cab
- Lighweight and portable

I used Dale Keller's excellent Newt program to design the scope and do ray tracing. You can see all my scope specifications and parameters here:

[ariefm71]

Here's the two-tube eq-mounted truss scope assembly.

[ariefm71]

Since I'll be using a 6-pole trusses, I need to calculate the length of the pole given the above parameters (tube diameters, horizontal length, etc). Here's the input I got from Cloudy Nights (thanks Dave!):

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d is the truss pole length.

d^2 = a^2 + b^2 + c^2.

You can use a = 22.84", the distance between the upper and lower truss connections.

b is essentially the chord between the 60 degree rotations of the truss pole mounts, allowing for their offset from the outside of the tube at the mounting points.

c can be 0 if you choose your reference line along the axis of the grid in your plans.

Attached is an illustration assuming 1" diameter truss poles, touching at the tips where they are mounted to the outside of the tube.
(The dark gray circles might be the lower attachment points, the light gray the upper attachment points)

In this example the centers of the poles, projected along the axis of the tube, are 5.66" apart, which is the "b" line.

So in this case, d^2 = 22.84^2 + 5.66^2: d = 23.53".

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To be safe, I ordered six anodized T-6061 1" OD aluminum truss pole with 26" length and a tube cutter to finely adjust the length.

[ariefm71]

Next will be pictures of the parts...

(You can make your comments now )

[elton]

Arief, is it ready yet? What type of imaging do you intend to do? If doing prime focus (deep sky) imaging, I notice that your imager must require less than 0.5" infocus, which is quite a tight fit given that you need some spare range to actually focus. I take it that you are using a flotation cell to support the mirror. Do also note that flotation cells do not give a fixed focus point -- as you collimate the mirror over time, the mirror may move up or down and shift the focus point. There is a possibility that if you collimate your mirror too high in the cell, your imager may not reach focus.

[ariefm71]

Hi Elton, it's "almost" ready, just waiting for one part only, the 3-vane protostar spider on its way now (it took one month for bryan to make , i have 4-vane astrosystems now).

The reason I choose the truss design is because of the flexibility of converting the scope from visual to imaging mode by using another set of six truss poles. The above schematics is for the "visual" mode.

cheers,
arief

[elton]

The 100% illuminated field is already very small. If the poles are shortened anymore, it will be even smaller. But as a planetary imager this would be pretty solid.

[ariefm71]

Components:

1. 10" f/5 Zambuto Primary Mirror. It's a privilege to own a mirror from one of the finest mirror makers of our time (Steve Kennedy is the other one, but he only makes 22" and above ). See pics here: http://www.singastro.org/viewtopic.php?t=2450&start=15
2. 1.83" ULS Quartz Protostar Secondary Mirror.
3. 9-point Kenneth Novak Mirror Cell. I might modify it to 6 points as recommended by PLOP.
4. Two pieces of 12" OD Carbon Fiber Tubes from http://www.carbonfibertubeshop.com . The lower tube is 24.46" long, the upper tube is 7.87" long.
5. Moonlite CR-1 focuser taken from my 7" newt (will upgrade later to CR-2)
6. Moonlite 1" OD aluminum T-6061 Truss poles (6 poles)
7. Moonlite Double Ball and Socket Truss Connectors (6 pieces) with custom made curved base.
8. Protostar Tube Flocking material
9. Protostar 3-vane spider
10. 12" ID Tube Rings and G11 dovetail from Ken's Rings (got used one from Astromart)
11. Fan module from Blue Sky Accesories (Floyd Blue)

[jermng]

Wow! Looks like an amazing project.
How long does it take on average to put together the scope after you've got all the components?
It looks like a whole new science to me. Don't think I'll have the patience to put something like that together ... even collimating my SCT is frustrating .. HAHA ...
Would this be less expensive compared to a "pre-made" scope from one of the premium dob makers?
Lot's of questions cos never knew anything bout ATM before.

BTW, how do you attach a truss dob to a mount? Hold it via one/two of the trusses?

[ariefm71]

How long does it take on average to put together the scope after you've got all the components?

A few weekends.

Would this be less expensive compared to a "pre-made" scope from one of the premium dob makers?

The only premium scope that meets my above design criteria (eq-mountable, etc) is a CPT 10" (http://www201.pair.com/resource/astro.h ... ducts/cpt/), but he asked US$3000 only for the structure (without any optics)! The Starmaster Versa 11" is too heavy (both on my mounts and my wallet)
If you want a normal dobsonian scope, you can get a 10" telekit or portaball with Zambuto mirror for slightly more than US$3000.

My other design goal is to be within my US$2000 budget (excluding shipping costs for the parts), or to put it bluntly, performance comparable to a 10" Mewlon for the price of an 8" Mewlon :-)

BTW, how do you attach a truss dob to a mount? Hold it via one/two of the trusses?

I'm using standard tube rings with G11 dovetail connected to the lower tube (see the schematics). The dovetail can be connected directly to my EM-100/Astroslew mount or can use a G11 to Tak saddle plate.