tabs of the mirror holder sit on the eyepiece side of the main body and cover
the whole width of the face of the tube. The two foot tabs sit similarly on the
opposite face. Push the mirror holder in until it is flush with the end of the
main body and secure the tabs with 4 paper clips.
Step 22
Now look through the eyepiece connector. Because of the dia-
phragms you should see a circular image through the other end of the tel-
escope. This circular image should be in the middle of the secondary mirror.
If the image is off to one side or the other, a slight pressure on the mirror in
the other direction should be sufficient to correct this. Luckily cardboard is a
very forgiving, error tolerant material... Do not stick the mirror holder in place
yet.
as Jupiter’s moon, so that the fine adjustment (step 56) can be skipped.
Step 29
Look through the eyepiece connector at the secondary mirror. If
construction was perfect, the main mirror will appear as a perfect round shape
with the square secondary mirror in its centre. Now move your eye back to a
point where the secondary mirror appears to completely fill the opening of
the eyepiece connector. Keep your eye directly vertical above the eyepiece.
If the secondary and main mirrors are correctly set up, the pupil of your eye
should appear in the middle of the secondary mirror and the centre mark-
ings of the main mirror should be in the middle of your pupil. See for yourself
which of the adjustment tabs needs to be moved a little bit in or out in order
for the mirrors, your pupil and the centre markings to be lined up correctly.
After the alignment the main mirror mounting should be just as far down in
the tube as it was before. The more exact the alignment, the better the ad-
justment of the main mirror. Secure the tabs once again with pegs.
Step 30
If your pupil is not in the centre of the secondary mirror there may be
various reasons:
1) The secondary mirror may not be directly under the eyepiece connector.
In this instance the secondary mirror holder needs to be pushed in or out of
the main body a small amount.
2) The secondary mirror is not exactly at 45 degrees to the axis of the main
body. In this case only the head or foot tabs of the holder need to be moved.
The Main Mirror
The main mirror has a 450mm focal length (abbreviated to ”f” from the Latin
focus
). That means it focuses parallel light to a point 450mm from its surface.
That would be about 28mm in front of the end of the main body if the second-
ary mirror had not diverted the light sideways into the eyepiece. The follow-
ing steps should be done carefully and slowly. The front surface of the mirror
is very susceptible to scratches and glue threads, despite the protective va-
pour-deposited quartz layer on top of the aluminium.
Step 23
Fold the six tabs of the main mirror base plate [E1]. to the back. At
the corners of each tab there are small handles. These are to facilitate ad-
justment of the mirror and are only cut-off later after successful set-up.
Step 24
Fold the 36 small tabs of the main mirror holder [E2] to the front and
make sure that the narrow hexagonal surround is not bent. Glue this hex-
agonal surround centrally onto the base plate [E1]. The tabs should not have
any glue on them. Press the piece flat until dry.
Step 25
Fold the tabs completely up so they form a sort of round fence,
apply glue to the inside edge as well as to the round inside of the base, and
insert the main mirror with its flat unsilvered side down. Only hold the mirror
by its edges and don’t touch the silvered surface. Apply a light tension with a
rubber band around the ring of tabs so they are pressed on evenly and lightly.
Put the whole assembly on a flat surface and apply a light pressure until dry.
Put a cloth between the mirror and any weight. It is important that the mirror
lies flat and even on the card.
Allow to dry completely before moving it.
Small amounts of adhesive at the edge of the mirror do not affect the optics
as a 5mm band around the edge is not used optically.
Step26
It is necessary for the adjustment to draw a small cross exactly in
the middle of the main mirror. The optical quality does not suffer because of
this mark because the secondary mirror keeps the light from falling onto the
centre region of the main mirror anyway. Measure exactly the centre point
with a set-square or a ruler and mark it with a thin felt-tip pen.
Step 27
Insert the main mirror holder assembly without any glue from the
back into the main body, mirror first. Push it in until the tabs are flush with the
end of the body and only the adjusting handles are sticking out. The main
mirror is now roughly pre-adjusted. Secure the tabs temporarily in place with
6 paper clips or wash pegs.
Step 28
Make sure the telescope opening is not pointed at the sun and look
into the eyepiece connector. Light from the front opening of the telescope is
now reflected by the main mirror. In
the middle of this circular patch of light
you can see the secondary mirror,
which appears to be square as it is
tilted at 45 degrees.
The Basic Adjustment
For terrestrial observations by day as
well as observing the moon’s craters
or sunspots on the sun the following
steps are normally sufficient. (Impor-
tant: You must use a sun filter to look
at the sun.) With some luck it will also
be good enough for the observation
of point light sources at night, such
The eyepieces
The two eyepieces have different focal lengths, namely f=15mm and f=28mm,
so that different magnifications are possible. The magnification is calculated
by the focal length of the main mirror divided by the focal length of the eye-
piece i.e. 450/15=30 and 450/28=16. The lenses made out of acrylic glass
are all plano-convex (one side is flat and the other curved outwards).
The 15mm eyepiece consists of two lenses with f=30mm and is called a
Ramsden eyepiece after its inventor. It can reduce the colour distortions of
the eye lens through the second lens called the Ramsden lens. The curved
side of this lens is facing the eye lens.
The 28mm eyepiece with three lenses has a particularly good colour correc-
tion and fringe focus.
Step 31
Only three of the five accompanying lenses have the same focal
length of
f=30mm, the fourth has a focal length of f=49mm and the fifth
f=65mm. Because they all look very similar and have the same diameter,
you must first establish which lens has which focal length.
Place each lens on printed paper with the curved side down. Raise them
slowly off the paper and when the ever increasing magnification suddenly
goes out of focus and turns upside down, the distance of the lens from the
paper corresponds to its focal length.
Step 32
Fold and glue the eyepiece shaft 15mm [F1] to form a hexagonal
tube, black side inward.
Step 33
Remove the small disc from the middle of the eye lens mounting for
the 15mm eyepiece [F2], resulting in a pupil. Fold the six tabs to the back.
Take one of the
f=30mm lenses and glue it with the flat side to the black
unprinted side of the eye lens mounting. Put a little glue on the mounting but
not too much and not as far as the edge of the pupil, otherwise it will be
squeezed onto the lens when the lens is pressed on the card. Place the lens
exactly central over the pupil. Leave to dry.
Step 34
Remove the Ramsden lens mounting [F3]. This is a narrow strip of
card. Fold all the grooves to the back and glue it to form a hexagonal ring.
After the eye lens [F2] has dried slide the ring [F3] over the lens. It should sit
fairly tightly and touch the lens mounting with its edge on all sides. Remove
the ring again, place a few drops of glue around the lens and slide the ring a
second time over the lens. Leave to dry.
Step 35
Now take a second
f=30mm lens. This is the Ramsden lens. Place
it, flat side down on your work surface. Turn the lens mounting upside down
and slide the open ring over the Ramsden lens. The curved surfaces of the
eye lens and Ramsden lens are now facing each other. Remove the Ram-
sden lens again, place a few drops of glue around the inside of the ring and
slide it once again over the Ramsden lens which, when the glue has dried,
should lie flush with the outside edge of the ring. Take care not to get any
glue on the surface of the lens. Leave to dry.
The head tabs of the mirror holder sit on the eyepiece side of the main body
and cover the whole width of the face of the tube. The two foot tabs sit
similarly on the opposite face. Push the mirror holder in until it is flush with
the end of the main body and secure the tabs with 4 paper clips.
Step 22
Now look through the eyepiece connector. Because of the
diaphragms you should see a circular image through the other end of the
telescope. This circular image should be in the middle of the secondary
mirror. If the image is off to one side or the other, a slight pressure on the
mirror in the other direction should be sufficient to correct this. Luckily
cardboard is a very forgiving, error-tolerant material. Do not glue the mirror
holder in place yet.
The Main Mirror
The main mirror has 450mm focal length (abbreviated to “f” from the Latin
“focus”). That means it focuses parallel light to a point 450mm from its
surface. That would be about 28mm in front of the end of the main body if
the secondary mirror had not diverted the light sideways into the eyepiece.
The following steps should be done carefully and slowly. The front surface
of the mirror is very susceptible to scratches and glue threads, despite the
protective vapour-deposited quartz layer on top of the aluminium.
Step 23
Fold the six tabs of the main mirror base plate [E1] to the back. At
the corners of each tab there are small handles. These are to facilitate
adjustment of the mirror and are only cut off later after successful setup.
Step 24
Fold the 36 small tabs of the main mirror holder [E2] to the front
and make sure that the narrow hexagonal surround is not bent. Glue this
hexagonal surround centrally onto the base plate [E1]. The tabs should not
have any glue on them. Press the piece flat until dry.
Step 25
Fold the tabs completely up so they form a sort of round fence,
apply glue to the inside edge as well as to the round inside of the base, and
insert the main mirror with its flat un-silvered side facing downwards. Only
hold the mirror by its edges and don
ʼ
t touch the silvered surface. Apply a
light tension with a rubber band around the ring of tabs so they are pressed
on evenly and lightly. Put the whole assembly on a flat surface and apply a
light pressure until dry. Put a cloth between the mirror and any weight. It is
important that the mirror lies flat and even on the card.
Allow to dry
completely before moving it.
Small amounts of adhesive at the edge of
the mirror do not affect the optics as a 5mm band around the edge is not
used optically.
Step 26
It is necessary for the adjustment to draw a small cross exactly in
the middle of the main mirror. The optical quality does not suffer because of
this mark, as the secondary mirror keeps the light from falling onto the
centre region of the main mirror anyway. Measure exactly the centre point
with a set-square or a ruler and mark it with a thin felt-tip pen.
Step 27
Insert the main mirror holder assembly without any glue from the
back into the main body, mirror first. Push it in until the tabs are flush with
the end of the body and only the adjusting handles are sticking out. The
main mirror is now roughly pre-adjusted. Secure the tabs temporarily in
place with 6 paper clips or clothes pegs.
Step 28
Make sure the telescope opening is not pointed at the sun and look
into the eyepiece connector. Light from the front opening of the telescope is
now reflected by the main mirror. In the middle of this circular patch of light
you can see the secondary mirror, which appears to be square as it is tilted
at 45 degrees.
The Basic Adjustment
For terrestrial observations by day as
well as observing the moon
ʼ
s craters or
sunspots on the sun the following steps
are normally sufficient. (
Important: You
must use a sun filter to look at the
sun!
) With some luck it will also be good
enough for the observation of point light
sources at night, such as Jupiter
ʼ
s
moons, so that the fine adjustment (Step
56) can be skipped.
tabs of the mirror holder sit on the eyepiece side of the main body and cover
the whole width of the face of the tube. The two foot tabs sit similarly on the
opposite face. Push the mirror holder in until it is flush with the end of the
main body and secure the tabs with 4 paper clips.
Step 22
Now look through the eyepiece connector. Because of the dia-
phragms you should see a circular image through the other end of the tel-
escope. This circular image should be in the middle of the secondary mirror.
If the image is off to one side or the other, a slight pressure on the mirror in
the other direction should be sufficient to correct this. Luckily cardboard is a
very forgiving, error tolerant material... Do not stick the mirror holder in place
yet.
as Jupiter’s moon, so that the fine adjustment (step 56) can be skipped.
Step 29
Look through the eyepiece connector at the secondary mirror. If
construction was perfect, the main mirror will appear as a perfect round shape
with the square secondary mirror in its centre. Now move your eye back to a
point where the secondary mirror appears to completely fill the opening of
the eyepiece connector. Keep your eye directly vertical above the eyepiece.
If the secondary and main mirrors are correctly set up, the pupil of your eye
should appear in the middle of the secondary mirror and the centre mark-
ings of the main mirror should be in the middle of your pupil. See for yourself
which of the adjustment tabs needs to be moved a little bit in or out in order
for the mirrors, your pupil and the centre markings to be lined up correctly.
After the alignment the main mirror mounting should be just as far down in
the tube as it was before. The more exact the alignment, the better the ad-
justment of the main mirror. Secure the tabs once again with pegs.
Step 30
If your pupil is not in the centre of the secondary mirror there may be
various reasons:
1) The secondary mirror may not be directly under the eyepiece connector.
In this instance the secondary mirror holder needs to be pushed in or out of
the main body a small amount.
2) The secondary mirror is not exactly at 45 degrees to the axis of the main
body. In this case only the head or foot tabs of the holder need to be moved.
The Main Mirror
The main mirror has a 450mm focal length (abbreviated to ”f” from the Latin
focus
). That means it focuses parallel light to a point 450mm from its surface.
That would be about 28mm in front of the end of the main body if the second-
ary mirror had not diverted the light sideways into the eyepiece. The follow-
ing steps should be done carefully and slowly. The front surface of the mirror
is very susceptible to scratches and glue threads, despite the protective va-
pour-deposited quartz layer on top of the aluminium.
Step 23
Fold the six tabs of the main mirror base plate [E1]. to the back. At
the corners of each tab there are small handles. These are to facilitate ad-
justment of the mirror and are only cut-off later after successful set-up.
Step 24
Fold the 36 small tabs of the main mirror holder [E2] to the front and
make sure that the narrow hexagonal surround is not bent. Glue this hex-
agonal surround centrally onto the base plate [E1]. The tabs should not have
any glue on them. Press the piece flat until dry.
Step 25
Fold the tabs completely up so they form a sort of round fence,
apply glue to the inside edge as well as to the round inside of the base, and
insert the main mirror with its flat unsilvered side down. Only hold the mirror
by its edges and don’t touch the silvered surface. Apply a light tension with a
rubber band around the ring of tabs so they are pressed on evenly and lightly.
Put the whole assembly on a flat surface and apply a light pressure until dry.
Put a cloth between the mirror and any weight. It is important that the mirror
lies flat and even on the card.
Allow to dry completely before moving it.
Small amounts of adhesive at the edge of the mirror do not affect the optics
as a 5mm band around the edge is not used optically.
Step26
It is necessary for the adjustment to draw a small cross exactly in
the middle of the main mirror. The optical quality does not suffer because of
this mark because the secondary mirror keeps the light from falling onto the
centre region of the main mirror anyway. Measure exactly the centre point
with a set-square or a ruler and mark it with a thin felt-tip pen.
Step 27
Insert the main mirror holder assembly without any glue from the
back into the main body, mirror first. Push it in until the tabs are flush with the
end of the body and only the adjusting handles are sticking out. The main
mirror is now roughly pre-adjusted. Secure the tabs temporarily in place with
6 paper clips or wash pegs.
Step 28
Make sure the telescope opening is not pointed at the sun and look
into the eyepiece connector. Light from the front opening of the telescope is
now reflected by the main mirror. In
the middle of this circular patch of light
you can see the secondary mirror,
which appears to be square as it is
tilted at 45 degrees.
The Basic Adjustment
For terrestrial observations by day as
well as observing the moon’s craters
or sunspots on the sun the following
steps are normally sufficient. (Impor-
tant: You must use a sun filter to look
at the sun.) With some luck it will also
be good enough for the observation
of point light sources at night, such
The eyepieces
The two eyepieces have different focal lengths, namely f=15mm and f=28mm,
so that different magnifications are possible. The magnification is calculated
by the focal length of the main mirror divided by the focal length of the eye-
piece i.e. 450/15=30 and 450/28=16. The lenses made out of acrylic glass
are all plano-convex (one side is flat and the other curved outwards).
The 15mm eyepiece consists of two lenses with f=30mm and is called a
Ramsden eyepiece after its inventor. It can reduce the colour distortions of
the eye lens through the second lens called the Ramsden lens. The curved
side of this lens is facing the eye lens.
The 28mm eyepiece with three lenses has a particularly good colour correc-
tion and fringe focus.
Step 31
Only three of the five accompanying lenses have the same focal
length of
f=30mm, the fourth has a focal length of f=49mm and the fifth
f=65mm. Because they all look very similar and have the same diameter,
you must first establish which lens has which focal length.
Place each lens on printed paper with the curved side down. Raise them
slowly off the paper and when the ever increasing magnification suddenly
goes out of focus and turns upside down, the distance of the lens from the
paper corresponds to its focal length.
Step 32
Fold and glue the eyepiece shaft 15mm [F1] to form a hexagonal
tube, black side inward.
Step 33
Remove the small disc from the middle of the eye lens mounting for
the 15mm eyepiece [F2], resulting in a pupil. Fold the six tabs to the back.
Take one of the
f=30mm lenses and glue it with the flat side to the black
unprinted side of the eye lens mounting. Put a little glue on the mounting but
not too much and not as far as the edge of the pupil, otherwise it will be
squeezed onto the lens when the lens is pressed on the card. Place the lens
exactly central over the pupil. Leave to dry.
Step 34
Remove the Ramsden lens mounting [F3]. This is a narrow strip of
card. Fold all the grooves to the back and glue it to form a hexagonal ring.
After the eye lens [F2] has dried slide the ring [F3] over the lens. It should sit
fairly tightly and touch the lens mounting with its edge on all sides. Remove
the ring again, place a few drops of glue around the lens and slide the ring a
second time over the lens. Leave to dry.
Step 35
Now take a second
f=30mm lens. This is the Ramsden lens. Place
it, flat side down on your work surface. Turn the lens mounting upside down
and slide the open ring over the Ramsden lens. The curved surfaces of the
eye lens and Ramsden lens are now facing each other. Remove the Ram-
sden lens again, place a few drops of glue around the inside of the ring and
slide it once again over the Ramsden lens which, when the glue has dried,
should lie flush with the outside edge of the ring. Take care not to get any
glue on the surface of the lens. Leave to dry.
Step 29
Look at the secondary mirror through the eyepiece connector. If the
construction was perfect, the main mirror will appear as a perfect round
shape with the square secondary mirror in its centre. Now move your eye
back to a point where the secondary mirror appears to completely fill the
opening of the eyepiece connector. Keep your eye directly vertical above
the eyepiece. If the secondary and main mirrors are correctly set up, the
pupil of your eye should appear in the middle of the secondary mirror and
the centre markings of the main mirror should be in the middle of your pupil.
Try out which of the adjustment tabs needs to be moved a little bit in or out
in order for the mirrors, your pupil, and the centre markings to be lined up
correctly. After the alignment the main mirror mounting should be just as far
down in the tube as it was before. The more exact the alignment, the better
the adjustment of the main mirror. Secure the tabs once again with pegs.
Step 30
If your pupil is not in the centre of the secondary mirror there may
be various reasons:
1) The secondary mirror may not be directly under the eyepiece connector.
In this instance the secondary mirror holder needs to be pushed in or out
of the main body by a small amount.
2) The secondary mirror is not exactly at 45 degrees to the axis of the main
body. In this case only the head or foot tabs of the holder need to be
moved.
The eyepieces
The two eyepieces have different focal lengths, namely f=15mm and
f=28mm, so that different magnifications are possible. The magnification is
calculated by the focal length of the main mirror divided by the focal length
of the eyepiece i.e. 450/15=30 and 450/28=16. The lenses made out of
acrylic glass are all planoconvex (one side is flat and the other curved
outwards).
The 15mm eyepiece consists of two lenses with f=30mm and is called a
Ramsden eyepiece after its inventor. It reduces the colour distortions of the
eye lens through the second lens called the Ramsden lens. The curved side
of this lens is facing the eye lens.
The 28mm eyepiece with three lenses has a particularly good colour
correction and fringe focus.
Step 31
Only three of the five accompanying lenses have the same focal
length of f=30mm, the fourth has a focal length of f=49mm, and the fifth of
f=65mm. Since they all look very similar and have the same diameter, you
must first establish which lens has which focal length.
Place each lens on printed paper with the curved side down. Raise them
slowly off the paper and when the ever-increasing magnification suddenly
goes out of focus and turns upside down, the distance of the lens from the
paper corresponds to its focal length.
Step 32
Fold and glue the eyepiece shaft 15mm [F1] to form a hexagonal
tube, black side inwards.
Step 33
Remove the small disc from the middle of the eye lens mounting
for the 15mm eyepiece [F2], resulting in a pupil. Fold the six tabs to the
back. Take one of the f=30mm lenses and glue it with the flat side to the
black unprinted side of the eye lens mounting. Put a little glue on the
mounting but not too much and not as far as the edge of the pupil,
otherwise it will be squeezed onto the lens when the lens is pressed on the
card. Place the lens exactly central over the pupil. Leave to dry.
Step 34
Remove the Ramsden lens mounting [F3]. This is a narrow strip of
card. Fold all the grooves to the back and glue it to form a hexagonal ring.
After the eye lens [F2] has dried slide the ring [F3] over the lens. It should
sit fairly tightly and touch the lens mounting with its edge on all sides.
Remove the ring again, place a few drops of glue around the lens and slide
the ring over the lens again. Leave to dry.
Step 35
Now take a second f=30mm lens. This is the Ramsden lens. Place
it flat side down on your work surface. Turn the lens mounting upside down
and slide the open ring over the Ramsden lens. The curved surfaces of the
eye lens and Ramsden lens are now facing each other. Remove the Rams-
den lens again, place a few drops of glue around the inside of the ring and
tabs of the mirror holder sit on the eyepiece side of the main body and cover
the whole width of the face of the tube. The two foot tabs sit similarly on the
opposite face. Push the mirror holder in until it is flush with the end of the
main body and secure the tabs with 4 paper clips.
Step 22
Now look through the eyepiece connector. Because of the dia-
phragms you should see a circular image through the other end of the tel-
escope. This circular image should be in the middle of the secondary mirror.
If the image is off to one side or the other, a slight pressure on the mirror in
the other direction should be sufficient to correct this. Luckily cardboard is a
very forgiving, error tolerant material... Do not stick the mirror holder in place
yet.
as Jupiter’s moon, so that the fine adjustment (step 56) can be skipped.
Step 29
Look through the eyepiece connector at the secondary mirror. If
construction was perfect, the main mirror will appear as a perfect round shape
with the square secondary mirror in its centre. Now move your eye back to a
point where the secondary mirror appears to completely fill the opening of
the eyepiece connector. Keep your eye directly vertical above the eyepiece.
If the secondary and main mirrors are correctly set up, the pupil of your eye
should appear in the middle of the secondary mirror and the centre mark-
ings of the main mirror should be in the middle of your pupil. See for yourself
which of the adjustment tabs needs to be moved a little bit in or out in order
for the mirrors, your pupil and the centre markings to be lined up correctly.
After the alignment the main mirror mounting should be just as far down in
the tube as it was before. The more exact the alignment, the better the ad-
justment of the main mirror. Secure the tabs once again with pegs.
Step 30
If your pupil is not in the centre of the secondary mirror there may be
various reasons:
1) The secondary mirror may not be directly under the eyepiece connector.
In this instance the secondary mirror holder needs to be pushed in or out of
the main body a small amount.
2) The secondary mirror is not exactly at 45 degrees to the axis of the main
body. In this case only the head or foot tabs of the holder need to be moved.
The Main Mirror
The main mirror has a 450mm focal length (abbreviated to ”f” from the Latin
focus
). That means it focuses parallel light to a point 450mm from its surface.
That would be about 28mm in front of the end of the main body if the second-
ary mirror had not diverted the light sideways into the eyepiece. The follow-
ing steps should be done carefully and slowly. The front surface of the mirror
is very susceptible to scratches and glue threads, despite the protective va-
pour-deposited quartz layer on top of the aluminium.
Step 23
Fold the six tabs of the main mirror base plate [E1]. to the back. At
the corners of each tab there are small handles. These are to facilitate ad-
justment of the mirror and are only cut-off later after successful set-up.
Step 24
Fold the 36 small tabs of the main mirror holder [E2] to the front and
make sure that the narrow hexagonal surround is not bent. Glue this hex-
agonal surround centrally onto the base plate [E1]. The tabs should not have
any glue on them. Press the piece flat until dry.
Step 25
Fold the tabs completely up so they form a sort of round fence,
apply glue to the inside edge as well as to the round inside of the base, and
insert the main mirror with its flat unsilvered side down. Only hold the mirror
by its edges and don’t touch the silvered surface. Apply a light tension with a
rubber band around the ring of tabs so they are pressed on evenly and lightly.
Put the whole assembly on a flat surface and apply a light pressure until dry.
Put a cloth between the mirror and any weight. It is important that the mirror
lies flat and even on the card.
Allow to dry completely before moving it.
Small amounts of adhesive at the edge of the mirror do not affect the optics
as a 5mm band around the edge is not used optically.
Step26
It is necessary for the adjustment to draw a small cross exactly in
the middle of the main mirror. The optical quality does not suffer because of
this mark because the secondary mirror keeps the light from falling onto the
centre region of the main mirror anyway. Measure exactly the centre point
with a set-square or a ruler and mark it with a thin felt-tip pen.
Step 27
Insert the main mirror holder assembly without any glue from the
back into the main body, mirror first. Push it in until the tabs are flush with the
end of the body and only the adjusting handles are sticking out. The main
mirror is now roughly pre-adjusted. Secure the tabs temporarily in place with
6 paper clips or wash pegs.
Step 28
Make sure the telescope opening is not pointed at the sun and look
into the eyepiece connector. Light from the front opening of the telescope is
now reflected by the main mirror. In
the middle of this circular patch of light
you can see the secondary mirror,
which appears to be square as it is
tilted at 45 degrees.
The Basic Adjustment
For terrestrial observations by day as
well as observing the moon’s craters
or sunspots on the sun the following
steps are normally sufficient. (Impor-
tant: You must use a sun filter to look
at the sun.) With some luck it will also
be good enough for the observation
of point light sources at night, such
The eyepieces
The two eyepieces have different focal lengths, namely f=15mm and f=28mm,
so that different magnifications are possible. The magnification is calculated
by the focal length of the main mirror divided by the focal length of the eye-
piece i.e. 450/15=30 and 450/28=16. The lenses made out of acrylic glass
are all plano-convex (one side is flat and the other curved outwards).
The 15mm eyepiece consists of two lenses with f=30mm and is called a
Ramsden eyepiece after its inventor. It can reduce the colour distortions of
the eye lens through the second lens called the Ramsden lens. The curved
side of this lens is facing the eye lens.
The 28mm eyepiece with three lenses has a particularly good colour correc-
tion and fringe focus.
Step 31
Only three of the five accompanying lenses have the same focal
length of
f
=30mm, the fourth has a focal length of
f
=49mm and the fifth
f
=65mm. Because they all look very similar and have the same diameter,
you must first establish which lens has which focal length.
Place each lens on printed paper with the curved side down. Raise them
slowly off the paper and when the ever increasing magnification suddenly
goes out of focus and turns upside down, the distance of the lens from the
paper corresponds to its focal length.
Step 32
Fold and glue the eyepiece shaft 15mm [F1] to form a hexagonal
tube, black side inward.
Step 33
Remove the small disc from the middle of the eye lens mounting for
the 15mm eyepiece [F2], resulting in a pupil. Fold the six tabs to the back.
Take one of the
f
=30mm lenses and glue it with the flat side to the black
unprinted side of the eye lens mounting. Put a little glue on the mounting but
not too much and not as far as the edge of the pupil, otherwise it will be
squeezed onto the lens when the lens is pressed on the card. Place the lens
exactly central over the pupil. Leave to dry.
Step 34
Remove the Ramsden lens mounting [F3]. This is a narrow strip of
card. Fold all the grooves to the back and glue it to form a hexagonal ring.
After the eye lens [F2] has dried slide the ring [F3] over the lens. It should sit
fairly tightly and touch the lens mounting with its edge on all sides. Remove
the ring again, place a few drops of glue around the lens and slide the ring a
second time over the lens. Leave to dry.
Step 35
Now take a second
f
=30mm lens. This is the Ramsden lens. Place
it, flat side down on your work surface. Turn the lens mounting upside down
and slide the open ring over the Ramsden lens. The curved surfaces of the
eye lens and Ramsden lens are now facing each other. Remove the Ram-
sden lens again, place a few drops of glue around the inside of the ring and
slide it once again over the Ramsden lens which, when the glue has dried,
should lie flush with the outside edge of the ring. Take care not to get any
glue on the surface of the lens. Leave to dry.
