DS-3 and DS-4 have ended up being such successful homebuilt
telescopes
that I
decided
to create a 20 inch homemade telescope using the same ultralight
design. This web page holds the results of these
efforts.
I also decided that
this web
page would generally just describe WHAT I did to make this lightweight
telescope, not HOW I did it. Weights and
dimensions
are near the bottom of this page.
I added a
conclusions and results section at the bottom of
this web page.
Finished scope. This picture shows one of the design requirements - no
need for a ladder. When straight up, the eyepiece is 74" high, and I
can use the telescope flat footed up to 55 degrees from the horizon. A
single step stool works at the zenith.
Here the finished scope is stacked for transport. Another design
requirement is
that the scope fits in the back of a hatchback.
Starting setup. Bearings are being attached to the mirror box.
The third design requirement is that I can move the scope by myself.
Moving the mirror box onto the rocker box. Mirror box, cell and 1 5/8"
20" mirror weighs 55 pounds, and about 60 pounds with the bearings.
Ground board and rocker box are in the background. Also note that the
mirror is covered and well protected.
Trusses go on the scope.
Secondary cage gets placed. Yet another design requirement is that the
scope be easy and quick to set up.
This next section details how I built the scope. It is mainly filled
with ideas and designs, not details. E-mail me if you have any
questions.
Mirror cell parts. This will be an 18 point suspension. Point locations
were calculated using Plop.
Mirror cell parts put together.
Mirror cell parts painted.
Mirror box bottom, with cell laid in place.
Mirror box. Total dimensions are 22"X22"X5".
Mirror box and mirror cell. Total mirror box, mirror cover and cell
weight is about
18 pounds. The mirror ended up weighing about 37, bringing the
total to 55 lbs.
This is all there is to the ground board and rocker box. The reason
that the rocker box doesn't have a back (for stiffening) is so I can
lift the mirror box out of the rocker box.
The upper cage. A wire spider and homemade secondary holder was
attempted, but really didn't work. It had vibration issues that were
unacceptable, and mechanically was problematic. I finally went with a
spider from Astrosystems. The commercial secondary holder was 3"
taller, necessitating changing the cage from 6" tall to 9" tall.
The upper cage and trusses, together. My neighbor is in the background
for scale. The trusses are somewhere around 6" too long in this
picture.
The total telescope in it's stored/travel configuration. The
cement mirror will be replaced with a quality mirror from OWL (Optic
Wave Labs). Once again, the secondary cage is 3" too short.
We now have some paint on the scope. Starting to take shape! The spider
has been replaced, due to vibration in the axis of the OTA.
Here I am next to the stored scope. This includes the base and rocker
box, with bearings removed.
Total
telescope:
Weight - Actuals
Name
Weight
Mirror, mirror box,
no bearings
55 lbs
Mirror, mirror box
and bearings
unknown lbs
Trusses
unknown lbs
Secondary cage
unknown lbs
Rocker box with
base
unknown lbs
Total
Telescope weight
unknown lbs
Total
weight of the OTA (Optical Tube Assembly)
unknown lbs
Total
weight of heaviest item (mirror and mirror box)
55 lbs
Dimensions
Height
of eyepiece at zenith
73"
Size
of mirror box and base, secondary, no bearings
26"X26"
Size
of mirror box and base, secondary, and bearings
