AT Dob Manual.pmd

astro-tech 8” & 10”
Do bsonians
from Astronomy Technologies
This instruction sheet will provide you with information on how to assemble your new reflector, and how to
properly maintain your telescope so it can give you a
lifetime of observing enjoyment.
Please familiarize yourself with your telescope’s parts
and functions before assembling it or operating it for
the first time.
Thank you for choosing this Astro-Tech Dobsonian reflector. While it is simply-made, it has precision optics
and an easily-assembled design that makes it an exceptionally good value in a large aperture telescope. Your
Astro-Tech Dobsonian will open for you a window on a
Universe of entrancing celestial viewing and years of
trouble-free observing enjoyment.
The Parts of
Your Astro-Tech
Dobsonian
Telescope
2
3
1
21
17
19
18
20
14
4
15
Optical Tube Assembly
1. Eyepiece
2. Focuser
3. Finderscope and quick-release bracket
4. Secondary mirror and spider assembly
5. Altitude bearing assembly and clutch knob
6. Optical tube
6
Rocker Box Assembly
7. Side panel (1 of 2)
8. Front panel
7
9. Lift handle
10. Eyepiece rack
8
11. Circular base (top)
12. Circular ground board (bottom)
9
13. Feet (3 beneath ground board)
16
5
Focuser Close-Up
10
11
13
12
Focuser Close-Up
14. Coarse focus knob
(1 of 2)
15. Fine focus knob
16. Focus lock & tension
adjustment knobs
17. 2” eyepiece holder
18. Thumbscrew
19. 2” eyepiece
20. Finderscope
21. Finder collimating screw
(1 of 2)
Assembling Your Astro-Tech Dobsonian
You will need a Phillips-head screwdriver to assemble
a few components of your scope. The hex head wrench
needed to assemble the majority of the scope
components is included with your telescope.
FIRST, ASSEMBLE THE ROCKER BOX
STEP 1: The rocker box supports the optical tube. It
allows you to move the tube up and down (in altitude)
and from side to side (in azimuth) so you can manually
find and track objects as they move across the sky.
Line up one of the rocker box side panels (part 7)
with the rocker box front panel (part 8) as shown. Thread
two of the self-tapping wood
8
screws through the assembly
7
holes in the side panel into
the pre-drilled holes in the
unfinished vertical edge of
Assembly
holes
the front panel to secure the
panels together. Tighten the
screws to a firm feel, but do
Holes for
not overtighten. Repeat with
eyepiece rack STEP 1A
the second rocker box side
panel (part 7), as shown right. STEP 1B
STEP 2: Turn the assembled
Assembly
holes
rocker box panels on their side.
Line up the circular base top
(part 11) that has the 7
predrilled holes against the
7
assembled front and side
panels, as shown below. Holes
8
H1 and H2 match up with the
pre-drilled holes in the unfinished underside of the right
side panel (part 7).
Assembled panels
Holes H3 and H4
from Step 1
H1
match up with the
The center hole
is not used
pre-drilled holes in
in this step
the underside of the
H6
front panel (part 8),
H2
H3
and holes H5 and H6
line up with the pre7
drilled holes in the
H4
H5
11
underside of the left
STEP 2
side panel (part 7).
1
Thread the remaining 6 self-tapping wood screws
through holes H1 through H6 in the circular base and
into the predrilled holes in the undersides of the front
and side panels. Tighten the screws to a firm feel, but
do not overtighten.
STEP 3: Get a few books of equal thickness or two
blocks of wood and place them on the floor parallel to
each other and about a foot apart. Sit the rocker box
you have assembled on the books or wood blocks so
the rocker box is raised off the floor and the previously
unused center hole is between the blocks.
Slide the tubular center bearing bushing into the center
hole of the circular base top (part 11) from above. The
bushing will be a tight fit, requiring a tap or two with a
hammer to fit it into place. Be sure the bushing lines up
at right angles to the circular base, and not at an angle,
before tapping it into place. A series of gentle taps are
all that will be needed. Tap the bushing into the circular
base until it projects about 1/4” to 3/8” past the
underside of the circular base to act as a guide for
assembling the components in the next step. Raising
the rocker box assembly off the floor with the books or
boards prevents you from gouging your floor as you tap
the bushing past the bottom of the circular base.
Do not use excessive force. A piece of heavy cardboard,
multiple layers of newspaper, or a thin board laid on top
of the bushing will protect the end of the bushing from
being dented if your tapping becomes too exuberant.
STEP 4: Take the rocker box off the books or boards
and lay it aside. Move the books out of the way. Place
the remaining circular ground board (part 12) on the
ground.
STEP 4A
The azimuth bearing
assembly consists of two
Assembled
rocker box
identical circular metal
roller bearing plates
11
(each with a hole in its
Roller
center) and a separate
bearing
circular roller bearing,
plate
also with a hole in its
12
center. The latter has
spokes and looks like a wagon wheel with dozens of
small tubular roller bearings set into its circumference.
Place the three roller bearing plates in a stack on the
ground board (part 12), aligning the holes in their centers
with the hole in the center of the ground board. First
place one of the two metal roller bearing plates on the
ground board, as shown in the Step 4A illustration above.
Next, lay the roller bearing (the plate that looks like a
wagon wheel) on top of the
Top
Roller
roller
bearing
first roller bearing plate,
bearing
in center
then place the second roller
plate
bearing plate on top of the
roller bearing itself, making
a roller bearing sandwich, as
Bottom
roller
shown in the Step 4B
bearing
illustration to the right. Be STEP 4B
plate
sure the central holes in the roller bearing sandwich
and the center hole in the ground board all line up.
It will help to have a second person assist you during
the next step. Place the rocker box assembly over the
roller bearing stack so that the tubular bushing projecting
through the circular base lines up with the holes in the
roller bearing stack and the ground board. Gently lower
the rocker box assembly until the tubular center bushing
slips through the holes in the roller bearing stack and
into the hole in the ground board.
Repeat the tapping of the tubular center bushing with
a hammer from the top side of the rocker box until the
top of the bushing is flush with the surface of the circular
base top (part 11) and fits securely into the hole in the
ground board. Be sure to observe all of the padding and
gentle tapping precautions mentioned previously when
doing this final tapping of the center bushing.
STEP 5: To secure the rocker box to the ground board,
use the hardware shown in the illustration below. Slide
the small washer onto the knob, followed by the small
roller bearing, and then
STEP 5
Knob
the large washer. Slide
Hole in rocker
box base with
the knob into the
bushing inserted
bushing that you have
tapped into the circular
base of the rocker box
Large washer
assembly and thread it
on bottom
into the lock nut that
was factory-installed Roller bearing
in middle
into the underside of
Small
the ground board. Be
washer
sure the large washer is on top
on the bottom of the
stack between the surface of the circular base of the
rocker box and the small roller bearing. Loosely handtighten the knob, but do not overtighten.
STEP 6: Next attach the three rubber feet to the
ground board. Tilt the rocker box assembly on its side.
Using a Phillips head screwdriver, screw one of the short
self-tapping wood screws through each foot into the predrilled holes in the ground board. Tighten to a firm feel.
STEP 7: Install the lift handle (part 9) by using the
supplied hex head wrench to thread the supplied bolts
through the handles and into the pre-drilled holes in the
front panel of the rocker box.
STEP 8: Sit the rocker box upright on the floor. Swivel
the rocker box from side to side on the ground board. It
should move easily, without any stiffness. If not, slightly
loosen the knob you installed in Step 6 until you achieve
the ease of motion you prefer.
STEP 9: The supplied eyepiece rack (part 10) can be
installed on the side panel of the rocker box, using the
supplied wood screws to fasten it to the two holes predrilled into the side panel.
NEXT, ASSEMBLE THE OPTICAL TUBE
STEP 10: With the rocker box resting upright on its
feet, place the optical tube into the rocker box. Make
2
The focuser has
STEP 12
Thumbscrew
separate lock and
Finder
Tube
tension knobs, as
and
tension
shown right. The
bracket
knob
lock knob allows
Coarse
extended observing
focus
knob
with very heavy
eyepieces without
focus shift. The
tension knob adjusts the drawtube
Fine
friction so you can
focus
knob
switch between a
Coarse focus knob Tube lock knob
variety of eyepieces
without having the heavier eyepieces drift out of focus.
STEP 13: The altitude bearings have been set at the
factory to balance a wide range of eyepiece weights
with the help of the altitude clutch knobs, which adjust
the freedom of tube motion up and down (in altitude).
However, if you have mostly heavy eyepieces in your
observing kit, you may want to adjust the tube balance.
Put your heaviest eyepiece in the focuser, lower the
optical tube until it is parallel with the ground, and loosen
the altitude clutch knobs. Note whether the eyepiece
end of the tube rises or falls when you let the tube go.
Lift the optical tube out of the rocker box and set it on
the ground. Note each bearing’s location on the scale
and loosen the balance
lock screws on the STEP 13
Scale
Balance lock
altitude bearings on
screw
either side of the tube.
If the nose of the
optical tube rose when
it was parallel to the
ground, the tube is tail
heavy. Slide the altitude
Clutch
bearings back (towards Altitude bearing
knob
the primary mirror) a
line or two on the scale on each side to shift the tube’s
center of gravity back. Tighten the balance locks. If the
nose of the optical tube sank, it is nose heavy. Slide the
altitude bearings slightly forward (towards the focuser)
and tighten in place. Put the optical tube back in the
rocker box and check the balance. Readjust the altitude
bearing positions as needed, being sure both altitude
bearings line up with the same scale markings.
STEP 14: A battery pack is provided to power the
built-in primary mirror cooling fan. The battery pack holds
eight AA batteries (not supplied). Alternatively, any
rechargeable battery pack with a 9 to 12VDC output
and a 5.5mm female power plug can be used to power
the fan. While the low-vibration fan can be left plugged
in and running continuously without affecting your
observing, it will deplete AA batteries quickly. Unplugging
the fan after mirror cooldown should be considered to
save your batteries if you use the battery pack.
STEP 15: Enjoy your scope!
sure that the U-shaped altitude ball bearing and clutch
knob assemblies are oriented properly to fit snugly down
into the U-shaped
STEP 10
openings on the side
Optical
tube
Altitude
panels of the rocker
clutch
box, as shown in the
knob
Seam
illustration to the
right. Also, make
Altitude
sure that the seam
bearing
assembly
on the optical tube is
pointing at the front
panel of the rocker
Front of
box. Leave the dust rocker
box
cover on the scope
to protect it until you are ready to observe.
The large ribbed altitude clutch knob that projects from
each altitude bearing assembly allows you to adjust the
amount of friction within the altitude bearing. This lets
you compensate for eyepieces of differing weights when
observing, by keeping the tube from slipping or drifting
in altitude when you switch between eyepieces.
STEP 11: Locate the finderscope, finderscope bracket,
and rubber O-ring supplied with the bracket. Slip the Oring over the 8 x 50mm finderscope body and slide it
forward until it rests in the groove in the body.
Loosen the two plastic collimating screws on the
finderscope bracket and slide the finderscope into the
bracket from the front until the rubber O-ring on the
finder seats firmly in the groove in the front of the
bracket. Tighten the collimation screws temporarily.
Slip the finder bracket
STEP 11
Finder
Collimating screw
bracket
into the mounting shoe
on the optical tube as
shown right and tighten
Mounting
shoe
the knob in the mounting
shoe to hold the bracket
in place. The finder’s two
nylon collimating screws
work in conjunction with
Tension
a tension spring in the
spring
bracket to make it easy
to collimate the finderscope with the main scope optics.
STEP 12: The dual-speed Crayford focuser has been
installed at the factory. If you wish to use the supplied
2” eyepiece, or any other 2” eyepiece you may have,
remove the 1.25” eyepiece adapter from the focuser
assembly by loosening the thumbscrew of the 2”
eyepiece holder (shown at the top of the next column).
Slide the 2” eyepiece into the focuser and tighten the
thumbscrew. To focus quickly, turn either of the coarse
focusing knobs. For very precise focus (for high
magnification observing, for example) use the single
smaller black fine focus knob.
To use the supplied 1.25” 9mm eyepiece, or any other
1.25” eyepieces you may have, replace the 1.25”
eyepiece adapter in the 2” eyepiece holder and tighten
the thumbscrew to hold it in place.
3
COLLIMATING YOUR SCOPE
Accurate mirror alignment is important to ensure the
peak performance of your telescope. For the best image
quality, the alignment of your telescope mirrors should
checked and adjusted as needed (i.e., collimated) on a
regular basis.
Although your Astro-Tech Dobsonian optical tube was
collimated at the factory, you should check collimation
before using it the first time to ensure that rough handling
in shipment has not altered the alignment of the mirrors.
Your scope uses a no-tool six-knob locking push/pull
primary mirror cell that reduces the need for frequent
collimation, but a quick check of the collimation (and
tweaking, if needed) should be a regular part of your
scope set-up routine, particularly if you routinely
transport your scope to a dark sky observing site.
While collimation can be done solely by eye as shown
here, optional tools (such as a Cheshire eyepiece, a
combined Cheshire eyepiece/sight tube, or a laser
collimator) will make the job easier and quicker.
The center of your scope’s primary mirror has been
marked with a donut-shaped sticker to make collimation
easier. This center mark is required for best results with
a Cheshire eyepiece or laser collimator. The center ring
sticker should not be removed from the primary mirror.
Because it lies directly in the shadow of the diagonal
mirror, it cannot be seen in the eyepiece and its presence
in no way affects the optical performance of your scope
or the image quality.
To check collimation by eye, remove the eyepiece and
look down the focuser drawtube. You should see the
diagonal mirror centered in the drawtube, as well as
the reflection of the primary mirror centered in the
diagonal mirror, and the reflection of the diagonal mirror
(and your eye) centered in the reflection of the primary
Bottom end of
focuser drawtube
Edge of
diagonal mirror
Reflection
of your eye
Primary
mirror
clip
mirror. You can identify the various parts in Figure A in
the previous column. Ignore the reflections for the time
being and start by examining the diagonal mirror, which
should be centered in the focuser drawtube.
If the diagonal is not centered in the focuser drawtube,
it may look similar to Figure B. If this is the case, it
needs to be adjusted.
This adjustment will
rarely, if ever, need to be
done, however. It helps
to adjust the diagonal
mirror in a brightly lit
room with the scope
pointed toward a bright
surface, such as a white
Bottom
or light-colored wall. Off-center
diagonal mirror
of drawtube
Placing a sheet of white
paper in the telescope tube opposite the focuser (i.e.,
behind the diagonal mirror) will also be helpful in
collimating the diagonal.
If the diagonal mirror is not directly under the focuser
drawtube fore and aft, loosen the three small alignment
set screws in the center hub of the 4-vaned spider several
turns. Holding the diagonal mirror holder stationary
(being careful not to touch the surface of the mirror),
turn the center screw in the center hub. Turning the
screw clockwise will move the diagonal mirror toward
the front opening of the optical tube, while turning the
screw counter-clockwise will move the diagonal mirror
back towards the primary mirror. DO NOT LOOSEN THE
CENTER SCREW TOO FAR. This screw attaches the mirror
holder to the spider. If it is unscrewed too far, it can
allow the diagonal mirror assembly to fall onto the
primary mirror, causing mirror damage that is not covered
by warranty.
When making these adjustments, be careful not to
stress the spider vanes or they may bend.
If the diagonal mirror is centered fore and aft under
the focuser drawtube, but is turned to one side or the
other, it will look like an oval, rather than a circle. Rotate
the diagonal mirror holder until the reflection of the
diagonal is circular and the primary mirror is centered in
the diagonal as much as possible. The primary may not
be perfectly centered, but that is acceptable if the
diagonal mirror appears circular. Now retighten the three
small alignment screws in the spider’s center hub equally
to secure the diagonal
mirror in that position.
If the entire primary
mirror reflection is not
visible in the circular
diagonal mirror, as in
Figure C, you will need
to adjust the tilt of the
diagonal mirror.
This is done by
Bottom
Diagonal
of drawtube
now centered
alternately loosening
Primary
mirror
center
donut
Diagonal
mirror holder
Spider
vane
Reflection
of primary
mirror
Figure A: Identifying the components seen
through the focuser drawtube
4
one of the three Eye not centered under donut
alignment setscrews in
the spider’s center hub Donut
while tightening the
other two. The goal is
to center the primary
mirror reflection in the
diagonal mirror, as in
Figure D. Don’t worry Diagonal
Primary
if the reflection of the centered
Bottom of drawtube
centered
diagonal mirror (and
your eye) is off-center, or not under the collimating donut,
as seen in Figure D. You will fix that in the next step.
The final adjustment is made to the tilt of the primary
mirror. It will need adjustment if, as in Figure D, the
diagonal mirror is centered under the focuser and the
reflection of the primary mirror is centered in the diagonal
mirror, but the small reflection of the diagonal mirror
and your eye is not under the collimating donut. This is
the collimation adjustment that is most likely to need
tweaking occasionally to maintain the best images.
The primary mirror tilt is adjusted with the three large
spring-loaded collimation thumbscrews on the back end
of the optical tube (bottom of the primary mirror cell).
The three smaller thumbscrews lock the mirror’s position
in place once it is collimated. These smaller thumbscrews
must be loosened before any collimation adjustments
can be made to the primary mirror.
To start, turn the smaller locking thumbscrews a few
turns each counterclockwise to loosen them. Now, try
tightening or loosening one of the larger collimation
thumbscrews to see the effect. Normally motions on
the order of 1/8 turn will make a difference, with only
about 1/2 to 3/4 turn being the maximum required. Do
NOT remove or back out the collimation screws more
than one to two turns! Look into the focuser and see if
the diagonal mirror reflection has moved closer to the
center of the primary. You can tell this easily with the
mirror collimation donut by simply watching to see if
the reflection of your eye is moving closer or farther
away from the donut on the center of the primary mirror.
When the reflection of Eye and collimation ring
your eye is centered in centered
the collimation donut,
your primary mirror is
collimated. The view
through the drawtube
should resemble Figure
E. Retighten the locking
thumbscrews.
Diagonal
Primary
For the sharpest
centered
centered
images, a simple star
test will let you perfect your collimation, but perfection
is not essential for casual backyard observing.
astro-tech
THE STAR TEST
Your telescope should be set up outside at night for
30 to 45 minutes before attempting collimation. Wait
for a night with good seeing conditions (cloudless skies,
calm air) and avoid looking over anything that produces
heat waves (i.e., roof tops, car hoods, etc.).
Collimation adjustments are best made while viewing
the star’s position in the field of view while simultanously
turning the adjustment screws. This way you can see
exactly in which direction the movement occurs. It is
helpful for two people to work together when collimating,
with one viewing and instructing the other which screws
to turn and by how much.
Point the telescope at a bright star and center it in the
eyepiece field of view. Study the image of the star while
racking it in and out of focus using 30 to 60 power per
inch of aperture (a 3mm or 4mm eyepiece). If the
telescope is correctly collimated, the star’s expanding
disk and diffraction rings should be a perfect circle on
either side of focus (the
F
left image in Figure F).
If you notice a flare to
one side of the star (the
right image in Figure F)
as you go inside and
outside of exact focus, then tweaking the collimation
will help sharpen the image.
Take note of the direction of the flare. For example, if
the flare is toward the 3 o’clock position in the field of
view (to the right), then you must adjust the screw or
combination of screws necessary to move the star
TOWARD the direction of the flaring. In this case, you
would want to use the adjusting screw or pair of screws
to move the star to the right, toward the 3 o’clock position
in the eyepiece field of view.
After making each adjustment, re-aim the telescope
tube to center the star again in the field of view. Once
again rack the scope focuser to either side of exact focus
and note the symmetry of the star’s pattern.
Improvement should be seen if the proper adjustments
have been made. You may have to adjust the screw or
screws several times to achieve the necessary direction
and amount of mirror movement.
If you try the star test and the bright star you have
selected is not accurately centered in the eyepiece, the
optics will always appear out of collimation, even though
they may be perfectly aligned. It is important to keep
the star precisely centered, so you will need to make
slight corrections to the telescope’s position over time
in order to account for the sky’s apparent motion.
Polaris, the North Star, is the perfect collimation star
for northern hemisphere observers since it appears
motionless against the background sky long enough to
perform the collimation procedure.
www.astronomytechnologies.com
from Astronomy Technologies, 110 East Main, Norman, OK 73069
© 2012 by Astronomy Technologies
Specifications, features, and descriptions are effective 6/1/2012, but are subject to correction and/or modification without notice and/or obligation.
5
ASTRO-TECH DOBSONIAN ROCKER BOX ASSEMBLY DIAGRAM
The parts designated by letters refer to the smaller
hidden assembly parts shown in the construction photos on Page 2 and the Parts List on Page 7.
The parts designated by numbers refer to the larger
visible parts shown in the main illustration on Page 1
and the construction photos on Pages 1 and 2.
I
J
K
7R
H
F
7L
10
8
Q
9
11
L
R
S
R
G
12
N
© 2010 by Astronomy Technologies
O
6
ASTRO-TECH DOBSONIAN ROCKER BOX PARTS LIST
The parts designated by letters refer to the smaller
hidden assembly parts shown in the construction photos on Page 2 and the Assembly Diagram on Page 6.
The parts designated by numbers refer to the larger
visible parts shown in the main illustration on Page 1
and the construction photos on Pages 1 and 2.
Rocker Box Wood Parts
Left Side Panel
Part 7L
Front Panel
Part 8
Right Side Panel
Part 7R
Circular Base (Top)
Part 11
Ground Board (Bottom)
Part 12
Rocker Box Hardware Parts
Roller Bearing
Plate Top
(1 of 2) Part R
5/16” - 18
Adjustment Knob
Part I
32mm Washer
Part F
Roller Bearing
Part S
Tubular Center
Bushing Part G
Roller Bearing
Plate Bottom
(2 of 2) Part R
16mm Washer Part J
15mm Roller Bearing
Part K
Eyepiece Rack
Part 10
Long
Self-Tapping
Wood Screws
(quantity 10)
Part H
Short Self-Tapping Wood
Screws (quantity 2)
Part Q
Lift Handle
Part 9
© 2010 by Astronomy Technologies
Plastic Feet
(quantity 3)
Part 13
1/4”-20 Machine Screws
(quantity 2) Part L
Short Self-Tapping
Wood Screws (quantity 3)
Part O
7