Sky-Watcher DOB10 User Manual

INSTRUCTION MANUAL

DOBSONIANS

150mm/1200mm
200mm/1200mm
254mm/1200mm

TABLE OF CONTENTS

Assembling Your Telescope

Parts List
Base Assembly
Optical Tube Assembly

Operating Your Telescope

Aligning the Finderscope
Focusing
Using the optional Barlow Lens
Using the Tension Control Handle
Pointing the Dobsonian
Calculating the Magnication (power)
Calculating the Field of View
Calculating the Exit Pupil

Observing the Sky

Sky Conditions
Selecting an Observing Site
Choosing the Best Time to Observe
Cooling the Telescope
Adopting Your Eyes

Proper Care for Your Telescope

3

3
4
5

6

6
6
6
7
7
8
8
8

9

9
9
9
9
9

10

Collimation
Cleaning Your Telescope

efore you begin

B

This instruction manual is applicable to all the models listed on the cover. Read the entire
manual carefully before beginning. Your telescope should be assembled during daylight
hours. Choose a large, open area to work to allow room for all parts to be unpacked.

aution!

C

NEVER USE YOUR TELESCOPE TO LOOK DIRECTLY AT THE SUN. PERMANENT
EYE DAMAGE WILL RESULT. USE A PROPER SOLAR FILTER FOR VIEWING THE
SUN. WHEN OBSERVING THE SUN, PLACE A DUST CAP OVER YOUR
FINDERSCOPE TO PROTECT IT FROM EXPOSURE. NEVER USE AN
EYEPIECE-TYPE SOLAR FILTER AND NEVER USE YOUR TELESCOPE TO
PROJECT SUNLIGHT ONTO ANOTHER SURFACE, THE INTERNAL HEAT BUILD-UP
WILL DAMAGE THE TELESCOPE OPTICAL ELEMENTS.

10
11

BASE ASSEMBLY

1. Connect the board B to the
board A1 and A2. Make sure
the logos on the board A1
and A2 are on the outside.
The side of the board B with
three small holes should be
facing the front.

Logo on the
other side

A2

A1

This side on
the outside

B

Logo

2. Connect the assembly
to the round board C.

Logo on the
other side

A2

A1

Logo

3. Attach the round plastic feet to board
D. Place the teflon pad in between
the assembly from step 2 and the
board D. Insert the black tube
from package 2 through the holes
in the centre of all the above.

Logo

C

D

4. Take the bolt from package 2 with a
washer on it and insert it through the
tube. Secure with second washer and
the nut using the two wrench provided.
Do not over-tighten the bolt. This will
prevent the mount base from freely
spinning on the bottom round board.

Logo

5. Position the accessory tray
over the 3 holes in the board
B and secure with the 3 small
screws provided.

C

6. Attach the handle from package
4 to the board B with the two
screws and the Alen wrench
from package 5.

7. Unassemble the cylindrical
saddle side bearings and the
screws from package 5. Attach
the cylindrical saddle side
bearings to the inside of board A
and A1 using the screws provided.

8. Cover all visible small screws with the screw caps provided

4

OPTICAL TUBE ASSEMBLY

9. Place the optical tube between the board
A1 and A2. Make sure that the side bearings
of the tube are rested on the 4 cylindrical
saddle side bearings.

10. Install the handles from package 7
into the holes on the board A1 and
A2. Do not over tighten the handles.
Make sure that the tension control
handle is installed on the same side
as the focuser for your convenience.

11. Locate the finderscope bracket
and carefully remove the rubber­ o-ring from it. Position the o-ring
into groove on the finderscope tube.

14. Remove the black plastic end-cap.
Loosen the thumbscrews on the
end of the focus tube if the end-cap
can not be removed.

12. Slide the finderscope bracket
into the mounting slot and tighten
the screw to hold the bracket in
place.

15. Insert the desired eyepiece
and lightly tighten the thumb­ screws to hold the eyepiece
in place.

13. Loosen the two adjusting
screws on the bracket. Position
the finderscope into its bracket
by sliding it backwards until
the rubber o-ring seats. Align
as described below

5

OPERATING YOUR TELESCOPE

ligning the Finderscope

A

ocusing

F

Fig.a

Fig.b

These fixed magnification scopes mounted on the optical tube are
very useful accessories. When they are correctly aligned with the
telescope, objects can be quickly located and brought to the centre
of the field. Alignment is best done outdoors in day light when it's
easier to locate objects. If it is necessary to refocus your
finderscope, sight on an object that is at least 500 yards (metres)
away. Loosen the locking ring by unscrewing it back towards the
bracket. The front lens holder can now be turned in and out to
focus. When focus is reached, lock it in position with the locking
ring (Fig.a).

1.

Choose a distant object that is at least 500 yards away and
point the main telescope at it. Adjust the telescope so that the
object is in the centre of the view in your eyepiece.

2.

Check the finderscope to see if the object centred in the main
telescope view is centred on the crosshairs.

3.

Use the two small alignment screws to centre the finderscope
crosshairs on the object. The screws work in opposition to a
spring-loaded knob (Fig.b).

Fig.c

Slowly turn the focus knobs (Fig.c), one way or the other, until the
image in the eyepiece is sharp. The image usually has to be
finely refocused over time, due to small variations caused by
temperature changes, flexures, etc. This often happens with short
focal ratio telescopes, particularly when they haven't yet reached
outside temperature. Refocusing is almost always necessary
when you change an eyepiece or add or remove a Barlow lens.

sing the Barlow lens (optional)

U

A Barlow is a negative lens which increases the magnifying power
of an eyepiece, while reducing the field of view. It expands the
cone of the focussed light before it reaches the focal point, so that
the telescope's focal length appears longer to the eyepiece. The
Barlow should be inserted between the focuser and the eyepiece
in your Dobsonian (Fig.d).

In addition to increasing magnification, the benefits of using a
Barlow lens include improved eye relief, and reduced spherical
aberration in the eyepiece. For this reason, a Barlow plus a lens
often outperform a single lens producing the same magnification.
However, it is greatest value may be that a Barlow can potentially
double the number of eyepiece in your collection.

Fig.d

Eyepiece

Barlow

6

Fig.e

sing the Tension Control Handle

U

Loosen or tightend the tension control handle to add just enough
friction to allow the tube to move easily when nudged but to stay
in position when not. It may be necessary to re-adjust the tension
control handle when accessories are added to, or removed from,
the tube. The tension control handle should be installed on the
same side as the eyepiece for your convenience. Leave the
handle on the other side slightly loose to allow full tension control
for the tension control handle (Fig.e).

ointing the Dobsonian

P

Pointing an altitude-azimuth (alt-az) mounted telescope, such as a Dobsonian, is relatively easy. With the
mount level, you can swivel the telescope around on a plane parallel to your horizon and then tilt it up and
down from there (Fig.f). You can think of it as turning your telescope in azimuth until it is facing the horizon
below a celestial object and then tilting it up to the object's altitude. However, the Earth rotates and
therefore the stars are constantly moving, so to track with this mount you have to constantly nudge the
optical tube in both azimuth and altitude to keep the object in the field.

In reference material for your local position, the altitude will be listed as ±degrees (minutes, seconds) above
or below your horizon. Azimuth may be listed by the cardinal compass points such as N, SW, ENE, etc., but
it is usually listed in 360 degree (minutes, seconds) steps clockwise from North (0°), with East, South and
West being 90°, 180° and 270 °, respectively (Fig.f).

tension control

Fig.f

(270°)

W

Zenith

Meridian
Line

Tilt in
Altitude

(0°/360°)

N

S

(180°)

Nadir

7

E

(90°)

Rotate in
Azimuth

alculating the Magnification (Power)

C

The magnification produced by a telescope is determined by the focal length of the eyepiece that is used
with it. To determine a magnification for your telescope, divide its focal length by the focal length of the
eyepieces you are going to use. For example, a 10mm focal length eyepiece will give 80X magnification
with an 800mm focal length telescope.

Focal length of the telescope

magnification =

When you are looking at astronomical objects, you are looking through a column of air that reaches to the
edge of space and that column seldom stays still. Similarly, when viewing over land you are often looking
through heat waves radiating from the ground, house, buildings, etc. Your telescope may be able to give
very high magnification but what you end up magnifying is all the turbulence between the telescope and the
subject. A good rule of thumb is that the usable magnification of a telescope is about 2X per mm of aperture
under good conditions.

alculating the Field of View

C

The size of the view that you see through your telescope is called the true (or actual) field of view and it is
determined by the design of the eyepiece. Every eyepiece has a value, called the apparent field of view,
which is supplied by the manufacturer. Field of view is usually measured in degrees and/or arc-minutes
(there are 60 arc-minutes in a degree). The true field of view produced by your telescope is calculated by
dividing the eyepiece's apparent field of view by the magnification that you previously calculated for the
combination. Using the figures in the previous magnification example, if your 10mm eyepiece has an
apparent field of view of 52 degrees, then the true field of view is 0.65 degrees or 39 arc-minutes.

Focal length of the eyepiece

=

800mm

10mm

= 80X

Apparent Field of View

True Field of View =

To put this in perspective, the moon is about 0.5° or 30 arc-minutes in diameter, so this combination would
be fine for viewing the whole moon with a little room to spare. Remember, too much magnification and too
small a field of view can make it very hard to find things. It is usually best to start at a lower magnification
with its wider field and then increase the magnification when you have found what you are looking for. First
find the moon then look at the shadows in the craters!

alculating the Exit Pupil

C

The Exit Pupil is the diameter (in mm) of the narrowest point of the cone of light leaving your telescope.
Knowing this value for a telescope-eyepiece combination tells you whether your eye is receiving all of the
light that your primary lens or mirror is providing. The average person has a fully dilated pupil diameter of
about 7mm. This value varies a bit from person to person, is less until your eyes become fully dark adapted
and decreases as you get older. To determine an exit pupil, you divide the diameter of the primary of your
telescope (in mm) by the magnification.

Diameter of Primary mirror in mm

Exit Pupil =

For example, a 200mm f/5 telescope with a 40mm eyepiece produces a magnification of 25x and an exit
pupil of 8mm. This combination can probably be used by a young person but would not be of much value to
a senior citizen. The same telescope used with a 32mm eyepiece gives a magnification of about 31x and an
exit pupil of 6.4mm which should be fine for most dark adapted eyes. In contrast, a 200mm f/10 telescope
with the 40mm eyepiece gives a magnification of 50x and an exit pupil of 4mm, which is fine for everyone.

Magnification

Magnification

=

52°

80X

=

0.65°

8

OBSERVING THE SKY

ky conditions

S

Sky conditions are usually defined by two atmospheric characteristics, seeing, or the steadiness of the air,
and transparency, light scattering due to the amount of water vapour and particulate material in the air.
When you observe the Moon and the planets, and they appear as though water is running over them, you
probably have bad "seeing" because you are observing through turbulent air. In conditions of good "seeing",
the stars appear steady, without twinkling, when you look at them with unassisted eyes (without a
telescope). Ideal "transparency" is when the sky is inky black and the air is unpolluted.

electing an observing site

S

Travel to the best site that is reasonably accessible. It should be away from city lights, and upwind from any
source of air pollution. Always choose as high an elevation as possible; this will get you above some of the
lights and pollution and will ensure that you aren't in any ground fog. Sometimes low fog banks help to block
light pollution if you get above them. Try to have a dark, unobstructed view of the horizon, especially the
southern horizon if you are in the Northern Hemisphere and vice versa. However, remember that the
darkest sky is usually at the "Zenith", directly above your head. It is the shortest path through the
atmosphere. Do not try to observe any object when the light path passes near any protrusion on the ground.
Even extremely light winds can cause major air turbulence as they flow over the top of a building or wall. If
you try to observe on any structure, or even a sidewalk, movements you make may cause the telescope to
vibrate. Pavement and concrete can also radiate stored heat which will affect observing.

Observing through a window is not recommended because the window glass will distort images
considerably. And an open window can be even worse, because warmer indoor air will escape out the
window, causing turbulence which also affects images. Astronomy is an outdoor activity.

hoosing the best time to observe

C

The best conditions will have still air, and obviously, a clear view of the sky. It is not necessary that the sky be
cloud-free. Often broken cloud conditions provide excellent seeing. Do not view immediately after sunset.
After the sun goes down, the Earth is still cooling, causing air turbulence. As the night goes on, not only will
seeing improve, but air pollution and ground lights will often diminish. Some of the best observing time is
often in the early morning hours. Objects are best observed as they cross the meridian, which is an imaginary
line that runs through the Zenith, due North-South. This is the point at which objects reach their highest points
in the sky. Observing at this time reduces bad atmospheric effects. When observing near the horizon, you
look through lots of atmosphere, complete with turbulence, dust particles and increased light pollution.

ooling the telescope

C

Telescopes require at least 10 to 30 minutes to cool down to outside air temperature. This may take longer
if there is a big difference between the temperature of the telescope and the outside air. This minimizes
heat wave distortion inside telescope tube (tube currents). Allow a longer cooling time for larger optics. If
you are using an equatorial mount, use this time for polar alignment.

dapting your eyes

A

Do not expose your eyes to anything except red light for 30 minutes prior to observing. This allows your
pupils to expand to their maximum diameter and build up the levels of optical pigments, which are rapidly
lost if exposed to bright light. It is important to observe with both eyes open. This avoids fatigue at the
eyepiece. If you find this too distracting, cover the non-used eye with your hand or an eye patch. Use
averted vision on faint objects: The center of your eye is the least sensitive to low light levels. When viewing
a faint object, don't look directly at it. Instead, look slightly to the side, and the object will appear brighter.

9

PROPER CARE FOR YOUR TELESCOPE

ollimation

C

Collimation is the process of aligning the mirrors of
your telescope so that they work in concert with each
other to deliver properly focused light to your eyepiece.
By observing out-of-focus star images, you can test
whether your telescope's optics are aligned. Place a
star in the centre of the field of view and move the
focuser so that the image is slightly out of focus. If the
seeing conditions are good, you will see a central circle
of light (the Airy disc) surrounded by a number of
diffraction rings. If the rings are symmetrical about the
Airy disc, the telescope's optics are correctly collimated
(Fig.g).

If you do not have a collimating tool, we suggest that
you make a "collimating cap" out of a plastic 35mm film
canister (black with gray lid). Drill or punch a small
pinhole in the exact center of the lid and cut off the
bottom of the canister. This device will keep your eye
centered of the focuser tube. Insert the collimating cap
into the focuser in place of a regular eyepiece.

Collimation is a painless process and works like this:

Pull off the lens cap which covers the front of the
telescope and look down the optical tube. At the bottom
you will see the primary mirror held in place by three
clips 120º apart, and at the top the small oval
secondary mirror held in a support and tilted 45º toward
the focuser outside the tube wall (Fig.h).

Fig.g

Correctly aligned

Fig.h

Primary mirror

Fig.i

Needs collimation

Focuser

Support for
secondary mirror

Secondary mirror

Primary
mirror

Mirror cell

The secondary mirror is aligned by adjusting the three
smaller screws surrounding the central bolt. The
primary mirror is adjusted by the three adjusting screws
at the back of your scope. The three locking screws
beside them serve to hold the mirror in place after
collimation. (Fig.i)

Aligning the Secondary Mirror

Point the telescope at a lit wall and insert the
collimating cap into the focuser in place of a regular
eyepiece. Look into the focuser through your
collimating cap. You may have to twist the focus knob a
few turns until the reflected image of the focuser is out
of your view. Note: keep your eye against the back of
the focus tube if collimating without a collimating cap.
Ignore the reflected image of the collimating cap or
your eye for now, instead look for the three clips
holding the primary mirror in place. If you can't see
them (Fig.j), it means that you will have to adjust the
three bolts on the top of the secondary mirror holder,
with possibly an Allen wrench or Phillip's screwdriver.
You will have to alternately loosen one and then
compensate for the slack by tightening the other two.
Stop when you see all three mirror clips (Fig.k). Make
sure that all three small alignment screws are tightened
to secure the secondary mirror in place.

Locking screw

Fig.j

Primary mirror clip

Fig.k

Primary mirror clip

Adjusting screw

Ignore the reflected
image for now

Primary mirror clip

10

Primary mirror clip

Aligning the Primary Mirror

There are 3 hex bolts and 3 Phillip's head screws
at the back of your telescope, for 150mm/1200mm
and 200mm/1200mm the hex bolts are the locking
screws and the Phillip's-head screws are the
adjusting screws. For 254mm/1200 the flat headed
screws are the adjusting screws and the
thumbscrews are the locking screws (Fig.l). Use an
Allen wrench to loosen the hex bolts by a few
turns. Now run your hand around the front of your
telescope keeping your eye to the focuser, you will
see the reflected image of your hand. The idea
here being to see which way the primary mirror is
defected, you do this by stopping at the point
where the reflected image of the secondary mirror
is closest to the primary mirrors' edge (Fig.m).

When you get to that point, stop and keep your
hand there while looking at the back end of your
telescope, is there an adjusting screw there? If
there is you will want to loosen it (turn the screw to
the left) to bring the mirror away from that point. If
there isn't a adjusting screw there, then go across
to the other side and tighten the adjusting screw on
the other side. This will gradually bring the mirror
into line until it looks like Fig.n. (It helps to have a
friend to help for primary mirror collimation. Have
your partner adjust the adjusting screws according
to your directions while you look in the focuser.)

hex bolt inside

Secondary
mirror

Primary mirror

Fig.l

Locking screw

Adjusting screw

Fig.m

stop and keep your
hand here

Fig.n

After dark go out and point your telescope at
Polaris, the North Star. With an eyepiece in the
focuser, take the image out of focus. You will see
the same image only now, it will be illuminated by
starlight. If necessary, repeat the collimating
process only keep the star centered while tweaking
the mirror.

leaning your telescope

C

Replace the dust cap over end of telescope whenever not in use. This prevents dust from settling on mirror
or lens surface. Do not clean mirror or lens unless you are familiar with optical surfaces. Clean finderscope
and eyepieces with special lens paper only. Eyepieces should be handled with care, avoid touching optical
surfaces.

Both mirrors aligned
with collimating cap in

Both mirrors aligned with
eye looking in focuser

TECHNICAL SUPPORT

Please contact your dealer for technical support.

11

aution

C

NEVER USE YOUR TELESCOPE TO LOOK DIRECTLY AT THE SUN. PERMANENT EYE
DAMAGE WILL RESULT. USE A PROPER SOLAR FILTER FOR VIEWING THE SUN. WHEN
OBSERVING THE SUN, PLACE A DUST CAP OVER YOUR FINDERSCOPE TO PROTECT IT
FROM EXPOSURE. NEVER USE AN EYEPIECE-TYPE SOLAR FILTER AND NEVER USE
YOUR TELESCOPE TO PROJECT SUNLIGHT ONTO ANOTHER SURFACE, THE INTERNAL
HEAT BUILD-UP WILL DAMAGE THE TELESCOPE OPTICAL ELEMENTS.

!

241202V1