C.A.L.D.

It takes a lot of trial and errors for an amateur astronomer to find or build his "ideal" telescope.
My ideal scope has to be easily transportable, no assembly required to setup, the tube should fit on the backseat of the car,decent optics and mechanics, and since I am a poor and inpatient star hopper, some sort of computer aid. A lightweight 200 mm F6 mirror was chosen, BK7 substrate, only 18 mm thick. Very fast cool down,  but still thick enough not to require a complicated mirror cell Semi open tube for reducing weight and lowering the scopes center of gravity. On such a tube, it was also convenient to make primary mirror collimation bolts at the front side, making it much less difficult, since you can see what you are doing in the focuser

Dobsonian mount made of light wood, azimuth bearing made with 3 roller bearings riding on a polished steel plate, and a center teflon glide bearing for that little friction needed. Tracking planets at high power is much easier this way than with a conventional Teflon - Formica az bearing

 

Computer Aided Lightweight Dobsonian


Overview and specifications:



Pictures taken at early stages of construction
 

The Mount

Standard Dobsonian mount with a few add-ons
Mount can be leveled by the adjustable feet,
 made from inexpensive clamps.
 An on board bubble level is also there.Altitude bearings are PVC plugs, 200mm diameter, riding on pads made from outdoor carpet.Az bearing seen from bottom side.
Note the 3 ball bearings mounted in the triangle corners



Also, a sliding counterweight
on the back of the tube --->

 

The Optical Tube  



Plywood mirror cell with 3 collimation counter screws and 3 rubber feet.
Still to install: a 12V fan into the 80 mm opening Threaded rods for primary mirror collimation are easily reachable while looking trough the focuser. Collimation is not turning the right bolt in the wrong direction or turning the wrong bolt in the right direction any more

Finder scope is made from a 50 mm binocular objective,some plumbing parts, screws and a 20 mm Kellner eyepiece.
Materials for the cross hair were found on my sisters hairbrush

Focuser is a modified "Meade" 2" plastic focuser. In its original state its very sloppy and too tall. I have shortened it for about 20 mm , and fixed the sloppiness by adding 2 thin teflon strips between the draw tube and focuser body.

A binoviewer comes to focus without the need of a barlow lens or path corrector. Just loosen the tube bolts, shorten the OTA for about 100 mm and no problem.Same with SLR camera
The Palm proved unpractical (tipping with stylus on a cold night wearing gloves) so I replaced it with my good old HP 1000 CX

 Full flash directly into the mirror, the tube obviously needs a anti reflection treatment... This is the old spider and old finder scope in the picture...
The CALD is only half the weight than the Meade 8" SCT with mount,  and takes less space in the car .
Not to mention the setup (or no setup )

Computer aid
 




To be able to point the telescope to the alt az coordinates calculated by the computer , a leveled mount and protractors with pointers are needed. They were printed out on paper and glued.
The pointers are made from furniture magnets, so they are adjustable.
When the mount is leveled, pick a easily identifiable object, like a planet or the Pleiads, read the alt az coordinates from the computer , point the telescope to the object, and adjust the pointers to show the values indicated by the computer.
Initialisation finished


Details and accesories


leveling feet detail
finderscope "alt-az" mount detail



Homemade eyepieces:
Left: 30 mm 6 element 2" 70 deg AFOV
Right: 24 mm 2" 7 element 75 deg AFOV
Homemade 2x Barlow, 19 mm Plossl
(45 deg AFOV) and 13 mm 6 element
(60 deg AFOV)
It is much nicer to look trough them than at them



Comercialy made 15 mm Plossl, 10 mm RKE,
and a 10  element 6.5 mm

10x50 binoculars
(don't leave home without them )