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16" f/4.5  dob

The intention with this telescope was to build a robust and powerful telescope using the relatively inexpensive 16 inch mirror sets produced by GSO. The concept for this 16" Dobsonian is a similar to that of my 22" Dob, except that it is of course smaller and somewhat simplified. Upper cage and mirror box are very similar, while mirror cell, altitude bearings, and rocker box were adapted to the smaller size of the telescope. The telescope has an eyepiece height of 168 cm. The heaviest part is the mirror box with 20 kg (including the 14 kg for the mirror). The telescope can therefore be handled easily by a single person and still gives that feeling of robustness.

I built this telescope for a friend, who owns a 16" Lightbridge, which was to heavy and bulky for transport in the car. The new telescope has a weight of not even half of that of the original Lightbridge despite of using the same heavy primary mirror.

More about planning and making of big Dobs is on these pages.

 

 

The upper cage ...

 

... is made of 15x15x1 mm aluminum square tubing and lined with thin plywood. The optical axis is bent downward by about 20, the telescope is hence a moderate Lowrider. 

The trusses are 20x1 mm aluminum poles connected pair wise by brackets and attached to the upper cage by quick-release fasteners.

The telescope has a wire spider of 0.8 mm steel, with crossed wires and an eccentric configuration.  The compact secondary holder allows to minimize lever forces. The secondary mirror can be heated with 0.6 W power using a 2 AA battery block.

 

More about wire spiders and secondary holders is here.

 

 

Behind the focuser  (Kineoptics HC 2) I mounted  a Moonlite filter slide.

The secondary cage baffles are made from PE sheet material which is painted flat black from one side and attached to the cage using patent fasteners (see here).

 

 

Even without a light shroud, stray light suppression is absolutely sufficient for a typical dark site as evident from the view down  the focuser.

 

 

 

 

 

The mirror box ...

 

 

... is made of 12 mm plywood with a 9 mm mirror baffle and 9 mm reinforcements in the back. Despite its low profile, it is very sturdy. The altitude bearings are made of 21 mm plywood. 

 

Both mirror and rocker box are etched in black and coated with several layers of transparent varnish.

 

More about making the mirror box is here.

The Truss

 

The lower truss clamps are similar as on Stathis' Cyclopas. The poles have adjustable stops that allow for precise adjustment of the position of the focal plane. The trusses are numbered, such that collimation of the Dobsonian is largely maintained after each set up. 

 

The poles are connected pairwise to attach to the secondary cage via quick release clamps.

 

More about the trusses and the blocks is here.

The mirror cell ...

 

... is a 6-poin cell made of 20x20x2 mm aluminum, which is sufficient for the 42 mm thick mirror.

 

 

 

 

The cell is attached permanently to the mirror box at one corner (the upper one) and can be collimated using the other two corners. 

The collimation bolts are accessible from the top, similar as with my 14" telescope.

 

 

 

 Lateral support is achieved using ball bearings adjustable to the center of gravity line of the mirror. 

16" Lowrider of our local astronomy club

 

This telescope has a very similar design, apart from being a moderate Lowrider (20), which lowers eyepice height to 150 cm. I have built this telescope for our local astronomy club to be used by our club members of for public outreach on our club's dark site..

 

 

Construction of the secondary cage and attachment of the focuser is similar as with my 22" Lowrider.

More about this telescope is here.

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