Building the ultimate travelscope: 10" f/4 ultra ultra compact truss Dob

[Roel]

This autumn I will be staying on the island of La Palma for a week of deep sky observing together with some of my observing buddy's. But what kind of telescope should I bring along? After lots of thoughts and some rough sketching I came up with what for me would be the ultimate travel scope...

Last week I started building a 10" truss telescope that would easily fit inside a normal backpack and be light enough to be carried to desolate mountain peaks or other exotic observing locations. I have also considered to make it a 12" but in the end I chose a 10" over a 12", because the latter would become just a bit too large and heavy for comfort. I really think a 10" might be the perfect combination of aperture and "compactness".

The focal ratio of f/4 is the fastest I can live with without the need for an expensive and heavy coma corrector. Also the viewing height at zenith will be around 3,3 feet - low enough to be used with one of those lightweight low folding seats. And last but not least: a short scope is a lot easier to balance -  I'll be using Vixen LVW eyepieces - pretty capable of handling fast mirrors, but not the lightest pieces of glass...

I started building the secondary ring. The 1.25" helical focuser is made out the inner workings of an old camera zoom lens. It has virtually no play, it's extremely lightweight and compact.

The total size of the transport case will be 28,5 x 30,5 x 9,8cm (11,2 x 12,0 x 3,9 inch), with the whole telescope in it, except for the trusses. I don't know what the total weight is going to be, but it will be well under 9 kg (20 lbs).

[mapstar]

Looking forward to seeing the scope progress going on your previous builds.

[JRM]

Roel,

Sounds like an awesome idea, light and portable, can not wait to see the finished product, will follow this thread with interest.

Rick

[swamp thing]

Looking forward to seeing the scope take shape  

[Soupy]

Oh... Sounds interesting, will follow with interest!

[Roel]

This is the primary mirror box/cell. Because of the thickness of the mirror a three point support is sufficient according to PLOP - which makes things definitely easier to build. The mirror simply rests on the tips of three nylon bolts. Just turn these bolts to collimate.

The box is simply a plywood plate with the truss connectors at the corners. Although the birch plywood is rigid enough for a very stiff stucture, I kept two corners attached to eachother for extra rigidity. The two altitute bearings will be bolted to the sides and will also add extra stiffness.

(I already applied some paint because I wanted to see what it will look like when finished.... It's a little rough, but in the end, after some sanding and extra layers, it will look a lot better.)

Next stop: the altitude bearings!

 

 

[mapstar]

As usual a lovely bit of woodworking Roel, black is a thumbs up from me 

 

 

[mountainstorm]

Really nice project; how are you planning to support/adjust your secondary?

[Moonshane]

This is beautiful work. I hope you are happy for people (i.e. me!) to take inspiration from the design?

[Moonshane]

ps, how do you fix the pieces? Biscuits or dowels? Or some other method?

[bomberbaz]

Question re the eyepieces, would it not have been better to use a decent zoom such as the pentax or leica? That said, the LVW are very nice

[Roel]

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how are you planning to support/adjust your secondary?

It's going to be the classic three push bolts/ one pull bolt system. Supperted by a three vane spider.

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how do you fix the pieces? Biscuits or dowels? Or some other method?

Just glue....

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would it not have been better to use a decent zoom such as the pentax or leica?

A Leica zoom is WAY over budget, and I'm very happy with the performance of my LVW's in fast telescopes (like my 14" f/4). They are also quite parfocal which means the travel of the focus can be very limited.

By the way, I finished the altitude bearings:

 

 

[bomberbaz]

4 minutes ago, Roel said:

It's going to be the classic three push bolts/ one pull bolt system. Supperted by a three vane spider.

Just glue....

A Leica zoom is WAY over budget, and I'm very happy with the performance of my LVW's in fast telescopes (like my 14" f/4). They are also quite parfocal which means the travel of the focus can be very limited.

By the way, I finished the altitude bearings:

 

 

very nice bearings, completed with weight reduction in mind i see. Keep the pictures coming 

[mapstar]

They look quite familiar, I may have a pair just like those in my garage 

[Roel]

This morning I finished the spider. It's a very simple three vane systeem with the well known push/pull collimation.

The vanes are very thin, which can be seen in the picture below. I placed the focuser a little bit more to the "top" instead of the common 45 degrees angle: It is a small telescope and while observing low above the horizon you'll get a much more comfortable viewing position.

 

[Samibotss]

Where do you get your  materials?

[mountainstorm]

Could we have a closeup shot of the collimation bolts on your secondary and how you fixed the veins into the hub?  Also, where did you get the thin strip metal for the veins.  I've been looking for something similar and the 1mm thick stuff stocked by my local DIY stores is closer to 2mm.

[bomberbaz]

13 minutes ago, mountainstorm said:

Could we have a closeup shot of the collimation bolts on your secondary and how you fixed the veins into the hub?  Also, where did you get the thin strip metal for the veins.  I've been looking for something similar and the 1mm thick stuff stocked by my local DIY stores is closer to 2mm.

save the picture to your pc, open with ms window picture manager and use the zoom, you can see it clearly. I do have a large screen monitor which helps tbf

[Roel]

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Where do you get your  materials?

From the local hardware store, and from the garbage container at my work....

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Could we have a closeup shot of the collimation bolts on your secondary and how you fixed the veins into the hub?  Also, where did you get the thin strip metal for the veins.

Top view:

Bottom view. Note the pointed tips of the (M4) collimation bolts, to prevent them from "skating" around while collimating. The spider vanes' tips are folded and hammered from above into a narrow slot in the hub. Very rigid connection!

The metal strips are packaging material, it is uses to strap heavyweight materials (like tiles and pavement) onto pallets. I pulled these from a garbage container at a construction site. Thickness about 0.5 mm.

 

[hughgilhespie]

20 hours ago, mountainstorm said:

Could we have a closeup shot of the collimation bolts on your secondary and how you fixed the veins into the hub?  Also, where did you get the thin strip metal for the veins.  I've been looking for something similar and the 1mm thick stuff stocked by my local DIY stores is closer to 2mm.

For the spider vanes, I used stainless steel rulers. I think mine came from Axminster Tools. The 6 inch / 150 mm ruler was very stiff and less than 1 mm thick plus it had a convenient hole in one end.

Regards, Hugh

[Moonshane]

2 hours ago, Roel said:

From the local hardware store, and from the garbage container at my work....

Top view:

Bottom view. Note the pointed tips of the (M4) collimation bolts, to prevent them from "skating" around while collimating. The spider vanes' tips are folded and hammered from above into a narrow slot in the hub. Very rigid connection!

The metal strips are packaging material, it is uses to strap heavyweight materials (like tiles and pavement) onto pallets. I pulled these from a garbage container at a construction site. Thickness about 0.5 mm.

 

Superb method and materials.

[bomberbaz]

Ingenious

[mountainstorm]

It'd be interesting to know more about your focuser; and particularly how well it performs - I like the old lens idea.  I'm always astounded at how focusers are either massive and heavy or cheap an flimsy.

[Roel]

Today I've cut the trusse to a few centimeters longer than calculated, and made the upper connectors (I'll post pictures of those in detail when finished). And I couldn't help myself making a quick layout on the floor, to see how the OTA will look when assembled. 

[Moonshane]

very graceful.