Why our instruments are unique

The telescopes made by THE DOBSON FACTORY include the most effective innovations in dobsonian making during the last 10 years.  All components have been tested by experienced amateurs. 

 

Our objective is to offer to the users an optimized instrument, in terms of rigidity, robustness, fluidity of motion, weight, compacity and transportability.

It is indeed possible to offer the same qualities offered by the old school massive dobsonian mounts, by adequately reducing the use of materials, optimizing the design, in order to minimise weight and enhance transportability, without any compromise on the quality of the building.
 
But be careful! The Devil is in the details! There are  to many lightweight instruments, with no adequate triangulation in the structure, lack of material when needed, no sense of the principals of structural engineering. They might work, sure, but they will not satisfy experienced amateurs!
 

Weight:
 
For mobile astronomers in search of dark skies, weight is a key point. 

Our 16" compact telescope weights 28 kg, including 11 kg for primary mirror and 17 kg for the structure. No individual part weights more than 8 kg.

The 20 " compact telescope weights 48 kg, including 22 kg for the primary mirror and 26 kg for the structure.

The 24" dobsonian scope weights 65 kg, including 30 kg for the primary mirror and 35 kg for the structure.

It is possible to make on demand more lightweight structures, using composite panels, with wood or carbon skins.  We can achieve that, without any compromise on stability and stiffness. Do not hesitate to ask.  


 
Choice of materials:

Our telescopes are made  with the adequate mixt of wood, aluminium, and carbon. 

Wood is indeed a marvelous material for telescope building, taking into account its anvibratory proprieties. We use high grade beech plywood from DELIGNIT, a German maker. Beech plywood is one of the hardest and stiffest plywood available, used by industrial modellists and piano makers.


All bolts, nuts and screws are made with stainless steel. The truss tubes can  be in aluminium (standard) or carbon (optional).
 
The wood parts are coated with 4 layers of marine coating. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
Base ring and flex rocker box:

The "old school" dobsonian telescopes are built with a heavy structure, moving on a small base. This is as if you put a large cabinet or wardrobe on a small tripod chair!

The telescopes made by THE DOBSON FACTORY stand on a large and very stiff ring ground base. The weight forces are directly transferred to this base by the flex rocker, without any torque. The base itself stands on 3 feet, well anchored on the ground floor.

This system gives an extreme stability to the whole structure.

 

 

 
 
 
 
 

The side-bearings:

In most of the dobsonian telescopes, the side bearings are small and narrow. This is indeed a key part of the telescope, and we prefer large and wide side-bearings, which give much more stability. 

Moreover,  large side-bearings will make the change of eyepieces easier. Taking into account the friction forces, the larger the diameter of the sidebearing, the easier the structure will be able to compensate the change in the center of gravity when removing a heavy eyepiece. Therefore, the scope will not move and the object you are looking at will still be in the center of the eyepiece!
 

Strengthenings between the side bearings:

In order to minimize the flexures of the side-bearing, we add a special T shaped part in-between. 

In traditional dobsonian building, the mirror box is the center part, which creates the rigidity of the whole structure. In a lightweight-oriented structure, each part has to generate the adequate stiffness.

 
 
 
Removable mirror box:

The mirror box can be easily removed, with the mirror inside, and obviously, without having to touch the mirror itself. You can hence disassemble the whole structure in small parts, which can be easily held and transported by hand. 

 

 
 
 
 
Fluidity and smoothness of motion, using Teflon and FRP:

 
FRP (fiber reinforced plastic) is a very good alternative to ebony star. It is even better for larger instruments.
 
 
 

The mirror cell:

The mirror cell frame is made of large aluminium beams (40 mm wide for 16" scopes, 60 mm wide for 24" scopes).

The cell floatation structure is optimised by PLOP simulations, according to the diameter, focal length, and width of the primary mirror (18 points for a 16" mirror, 27 points for a 24" one).


 
 
 
 
 
Mirror adjustment is made easy with large bolts, easily held in hand

 
 

There are several ways of supporting the primary mirror laterally: A sling, a cable or two  strong supports. The sling can create astigmatism, the cable is sometimes difficult to arrange. We therefore prefer the system with  2 strong lateral supports, fixed à 45°,  with a roller  supporting tangentially the edge of the mirror. 

 

 
Assembling the focuser holder:

Special attention is dedicated to the stiffness of the upper ring, and focuser holder. This one is made as a box, with lateral walls, which minimizes flexures. Heavy eyepieces can be used in the same ways as in classical double rings cage.
 
 
 
 
 
Truss assembly:

 The way the truss is connected together is one of the key factor in order to give to a dobsonian telescope its stiffness and rigidity. We have tested many systems, and came to the conclusion that the "ball and socket" system is the best adapted, in term of viability, rigidity and facility to assemble.

When the balls are pressed in their socket, there is no way for them to move. 
 
The tubes are assembled by pair, and the full assembling of the scope does not take more than 10 minutes!

 
 
 
 
 
 
 
 
 
 
 
 
 Assembling the truss

 
 
Spider and secondaryholder:

 
 
 
 
 Easy and very fine alignment of the secondary with 3 large buttons
 
 

Protecting the secondary mirror:

 
 
Light protection:
 
 Light screen on the secondary ring


Custom fitted light shroud
 

Digital encoders and driving system:

 
 
 
 
 
 
 

Motors and electronic devices are full integrated in the structure





How to move the telescope:

The smaller instruments (up to 18 ") can be disassembled in several pieces, no part is heavier than 10 kg and carried indivually.
It is also possible to use a 2 wheels dolly:



For larger telescopes, the most convenient way is a 4 wheels system. The instrument can be rolled on the ground, and even push into the car. The 4 wheels are easily removed during observing time.









Equatorial plateform:



THE DOBSON FACTORY makes on demand specially dedicated low profile equatorial platforms, designed in order to minimize the added height.