KLAUS HUNIG AstroMedia 240.BLT User manual

Shopping list for
the DIY store:
■
1 piece of drain pipe, 40mm diameter,
about 430mm long, preferably black, e.g.
Marley (B&Q) (for the telescope tube)
■
2 push t couplings, 40mm, preferably
black, e.g. Marley WPC4BX (B&Q)
(to hold the objective lens and the eyepiece)
■
1 push t socket plug, 40mm (1 1/2”), e.g.
POLYPIPE WP30B (for the eyepiece)
The Plumber’s
Telescope
Kit for an astronomical refracting telescope with
30x magnication, using 40mm drain pipes
from any local DIY store
Achromatic objective lens,
Ø 40mm, f +450mm
Colour corrected Plössl eyepiece,
Ø 15mm, f +15mm
Tripod adapter (without tripod)
Indestructible HT tubing
Shows Moon craters, phases
of Venus, Moons of Jupiter,
etc with 30x magnication
Easy to assemble
AstroMedia Verlag • Made in Germany • © Klaus Hünig
Translation: Andreas Schröer
Article-No. 240.BLT
KLAUS HÜNIG

The telescope was invented in 1608 by a Dutch
spectacles maker. He held a concave lens
(used for short-sightedness) in front of his eye
and a convex lens (for far-sightedness) towards
an object. With the correct distance between the
lenses he could see a magnied picture of the
object. Galileo Galilei was the rst person to use
a telescope for science in 1609. His telescope
design has the advantage of an upright picture,
but also the crucial disadvantage that the eld
of view becomes increasingly smaller with in-
creasing magnication. This is the reason that
today all astronomical refracting telescopes are
built according to the design of the great math-
ematician and astronomer Johannes Kepler. In
1611 he described a telescope that uses two
convex lenses, which allows high magnication
with a large eld of view. The picture is upside
down, but that is of course no disadvantage
for astronomical observations. This “Plumber‘s
Telescope” uses Kepler‘s principle too, but with
high quality achromatic lenses of which Kepler
wouldn‘t even have dreamt. The colour cor-
recting properties come from the combination
of two lenses with different refractivity which
are cemented together to form one achromatic
lens. Each of the parts on its own would have
great chromatic errors, in combination though
these errors cancel out.
This kit contains:
■1 achromatic lens, 40mm diameter, 450mm
focal length
■2 achromatic lenses, 15mm diameter,
26.5mm focal length, to build a Plössl eye-
piece with 15mm focal length
■4 pre-cut pieces of black cardboard
■1 tripod adapter
What you need for completion:
■1 piece of drain pipe, 40mm diameter, about
430mm long, preferably black, e.g. Mar-
ley/B&Q (for the telescope tube)
■ 2 push t couplings, 40mm, preferably black,
e.g. Marley/B&Q (to hold the objective lens
and the eyepiece)
■ 1 push t socket plug, 40mm (1 1/2”), e.g.
POLYPIPE WP30B (for the eyepiece)
■A small hacksaw to shorten the waste pipe
to the correct length
■A drill and drill bits to drill the 10mm hole of
the eyepiece (you can also use a nail or a
small cross headed screw driver to open the
hole and then widen it with a pair of scissors).
■Sticky tape for the eyepiece
■ Strong sticky tape (gaffer / duct / insulation
tape) to t the telescope to the tripod adapter
■Solvent-containing all-purpose glue (not
water based)
■A sharp knife (scalpel or small carpet knife)
■ A piece of ne grade sandpaper to smooth
the cuts
Assembly instructions:
Please always read completely through each
step before commencing.
A. The objective lens tube
The objective lens (or combination of lenses)
is the one pointing towards the observed ob-
ject, the one through which the light enters the
telescope. It ts just over the end of the waste
pipe and is secured in place with one of the
push t couplings.
Step 1:
Cut the waste pipe to 430mm ± 2mm using the
hack saw. To get a nice straight line at the right
length, wrap a piece of paper around the pipe
and mark the line to cut with a pencil along the
edge of the paper. Cut all around the line, not
just straight through from one side. Smooth the

edge of the pipe with sandpaper. This end of
the objective lens tube will be the end holding
the eyepiece. Stand the tube with the cut end
down on the work surface.
Step 2:
Now place the objective lens on top of the tube
with the greater curved side facing upwards.
Take care never to touch the surface of the lens,
only handle it by its sides. From the side you
can see that the lens is made from two single
lenses. The thinner one of these two has to face
upwards. Now carefully t one of the couplings
over the lens and push it rmly down until it
holds the lens tightly in place. This nishes the
construction of the objective lens tube.
B. The eyepiece
The eyepiece is the lens (or combination of
lenses) through which you look with your eye.
The Plössl eyepiece was invented in 1860 by
the Viennese optician Simon Plössl. It is one of
the best eyepieces available because it produces
a fully colour corrected and sharp image with a
large eld of view. It is made from two identical
achromatic lenses that are mounted in a short
tube with their rounded sides facing each other.
Step 3:
Remove Part A (eyepiece tube) from the black
piece of cardboard. Don‘t tear it out, use a sharp
knife or scalpel to cut the remaining bits that
retain the part in the cardboard. Crease and
fold Part A to form a hexagonal tube, connecting
the ends with a piece of sticky tape. Put the two
eyepiece lenses with their at sides down on a
clean work surface. Try tting
the tube over one of the lenses
and check that it holds the lens
when you pick it up. If not, bend
the six sides slightly inwards.
Take the lens out again. Put
a small amount of all-purpose
glue on all sides of the inside of
the end of the tube. Distribute
the glue evenly and avoid any
drops or glue strings. Then
carefully t the tube on the lens again so that
the edges stand squarely on the work surface
and the lens is glued into the tube. Do this very
carefully so that no glue gets onto the lens
surfaces. After the glue has set, glue the other
lens into the opposite end of the tube, following
the same procedure. Now the two curved sides
of the lenses face each other
inside the tube with a distance
of about 1mm. With this your
Plössl eyepiece is nished. It
now needs a holder to t it into
the telescope.
Step 4:
Remove Part B (tube holder)
from the cardboard, again
using a knife to do so.
Crease and fold it to form
a hexagonal tube and con-
nect the ends with the ends
with sticky tape. Fold the six
tags outwards and check
that the eye piece ts snugly into the holder.

Put a small amount of glue evenly around the
inner side of the end with the tags, again without
drops or strings. Push the eyepiece into the
holder from the tag side and slide it into place
by pushing it onto the work surface so it is ush
with the six tags.
Step 5:
Open the 11mm central hole in Part C (blind),
using a sharp knife, and then remove the part
from the cardboard. Fold the six tags back-
wards and glue the part onto the end of the
holder, opposite the eyepiece.
Step 6:
Open the 10mm central hole
in Part D (mounting disk)
using a sharp knife and then
remove the part from the
cardboard. Glue the eyepiece
holder centrally onto the disk
using the tags so that the
eyepiece lens is exactly
over the hole. Now the
Plössl eyepiece is ready
to be mounted in the eye-
piece holder.
C. The eyepiece holder
The eyepiece holder is the piece of tubing that
holds the eyepiece and needs to slide on the
objective lens tube for focusing. Unlike on other
telescopes, the eyepiece holder slides OVER
the objective lens tube.
Step 7:
Drill or le a 10mm hole into the exact centre
of the socket plug. The material is quite soft,
so if you don‘t have a drill, you can use a small
cross-headed screw driver to make a hole and
then enlarge it with a blade of a pair of scissors.
It doesn‘t matter if the hole is a bit bigger than
10mm. Use sandpaper to smooth the hole and
then roughen the inside of the plug to provide
a good base for the glue. Remove all dust and
loose plastic bits.
Step 8:
Apply a generous amount of glue onto the disk
holding the eyepiece and t it into the socket
plug so that the hole in the disk sits centrally
over the hole in the plug. Again take care that
no glue gets onto the surface of the lens. After
the glue has set, push the plug into the second
push-t coupling. This nishes the construction
of the eyepiece holder.
D. The nal assembly
Step 9:
Remove the rubber seal from the open end
of the eyepiece holder. Then t the eyepiece
holder on the open end of the objective lens
tube. See if you can focus on a distant object
by moving it in or out. If not, you will have to
shorten the objective lens tube by a few more
millimeters. Since the focal length of the lenses
can differ slightly and the adjustment also has
to compensate for spectacles, each telescope
has to be adjusted individually.
Step 10:
If the eyepiece holder moves too easily, a few
strips of sticky tape can be applied to the tube
to increase its diameter.
Step 11:
Lastly t the tripod adapter to the tube with some
strong sticky tape. If you want to improve the
properties of your telescope, you can t a rolled-
up piece of black carton inside the objective lens
tube to reduce light reections.
Congratulations, you have nished your
Plumber‘s Telescope!
We wish you good luck for your “First Light”
(as astronomers call the very rst use of a
new telescope).