ASTRONZ DOBSONIAN GS680 User manual

OWNER’S MANUAL
DOBSONIAN TELESCOPE
ASTRONZ GS680 200mm ( 8”) F/6
ASTRONZ GS880 254mm (10”) F/5
ASTRONZ GS980 303mm (12”) F/5

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Astronz (Astronomy NZ Ltd) is fully owned by the Auckland
Astronomical Society and operated by its members.
Our mission is to supply quality telescopes and accessories
at a reasonable price. By importing and selling direct from
the manufacturer to the customer we can keep our prices
down and give you the best value on the New Zealand
market.
As passionate astronomers ourselves, we understand how
important it is to have the highest quality, precision optics.
Our speciality is in easy to use instruments that can be
used for real astronomy, and not outgrown in a matter of
months.
Astronz supports astronomy throughout New Zealand and
continues to invest its prots back into the astronomical
community nationwide.

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Contents
Introduction 4
Specication 5
Parts 6
Assembly 7
Using your Telescope 10
Focuser 10
Eyepieces 10
Finderscope 11
Observation Tips 12
Selecting a SIte 12
Cooling 12
Seeing 12
Storage 13
Maintainence 13

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Thank you for purchasing an Astronz Dobsonian
telescope. This precision optical instrument is built
with the highest quality materials and with proper
care will provide many years of reliable service.
The Dobsonian telescope is an “alt-azimuth” (up-down/
left-right) mounted Newtonian reector type telescope.
The design was popularised in the 1960’s by San Francisco
astronomer John Dobson, who famously made telescopes
from recycled “junk” such as cardboard tubes and scrap
wood, and was largely responsible for making large aperture
telescopes available to amateur astronomers for a reasonable
cost.
In a Newtonian reector telescope, invented by British scientist Sir
Issac Newton (1642-1727), light enters the telescope throught the top
of the telescope (the open end) and is reected o󰀨 a concave parabolic
curved mirror at the bottom of the tube. The light is then reected o󰀨 a at
mirror mounted at an angle of 45 degrees, into an eypiece on the side of the
telescope tube.
Introduction
⚠ WARNING
DO NOT use the telescope or nderscope to look at the sun with-
out an approved solar lter. Doing so will cause permanent dam-
age and even blindness.
NEVER use a solar lter that attaches to the eyepiece. Only
approved solar lters that completely cover the opening of the
optical tube will provide adequate protection.

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Finderscope
Focuser
Focus Adjustment
Altitude Bearing
Azimuth Bearing
Optical Tube Assembly
(OTA)
Dobsonian Base
Cooling Fan
Collimation Screws
GS680
Focal Length: 1200mm
Focal Ratio: f/6
Aperture: 200mm
Weight: Telescope 13kg
Base 10kg
Length: Telescope 1.25m
Magnication: 9mm EP 133x
30mm EP 40x
GS880
Focal Length: 1250mm
Focal Ratio: f/5
Aperture: 254mm
Weight: Telescope 18kg
Base 12kg
Length: Telescope 1.35m
Magnication: 9mm EP 139x
30mm EP 42x
GS980
Focal Length: 1500mm
Focal Ratio: f/5
Aperture: 303mm
Weight: Telescope 22kg
Base 14kg
Length: Telescope 1.45m
Magnication: 9mm EP 167x
30mm EP 50x
Specications
Telescope: Newtonian Reector Optical Tube Assembly.
Mirror: BK7 glass, parabolic, with mirror surface quality over 1/16 wave RMS. Cooling fan.
Mount: Dobsonian base with brake / tension system. Roller bearings for smooth movement.
Focuser: 2” Dual Speed 10:1 Crayford Focuser. 1.25” to 2” Adapter.
Supplied Accessories:
9mm Plossl 1.25” Eyepiece
30mm Superview 2” Eyepiece
2” Extension Tube

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Unbox all parts for the base assembly and identify all the parts below:
A. Base Sides (2) F. Handle (and screws)
B. Base Front G. Feet (and screws) (3)
C. Upper Base Plates H. Long Screws (10)
D Lower Base Plate I. Eyepiece Tray (and screws)
E. Bearing Plates (3) J. Adjustment Bolt (wih large and small washers,
ball bearing and bushing)
A B C D
E F G
H I J
Base Assembly

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Step 1: Screw the handle (F)
to the Base Front (B) using the
provided screws into the pre-
drilled holes.
Step 2: Screw the two Base
Sides (A) to the Base Front
(B) using the Long Screws (H)
Ensure the sides are rmly at-
tached, but do not overtighten.
Step 3: Flip the assembled
sides upside down and secure
to the Upper Base Plate (C) us-
ing Long Screws (H) (note: the
Upper Base Plate has a center
hole and six predrilled holes.
Ensure that the recessed holes
are facing away from the hous-
ing so screw heads can be ush)
Step 4: Attach feet (G) to the Lower Base
Plate (D) (note: this is the one with the brass
insert in the centre and three pre-drilled holes
for the feet.)
Step 5: Flip the Lower Base Plate over onto
its feet and insert the metal bushing (sleeve)
from the Adjustment Bolt into the centre hole
Step 6: Place the Bearing Plates (E) onto the
bushing ensurung they are kept in the correct
order (the plate with the metal roller bearings
sandwiched between the other two plates
Step 7: The whole assembly from Step 3 should now also be carefully lifted onto the bushing, and
should rotate freely
Step 8: Assemble the Adjustement Bolt (J) in the following order: Bolt -Small Washer - Ball Bear-
ing - Large Washer and insert into the bushing to secure all the base plate parts together
Step 9: The nal step is to install the Eyepiece Tray (I) to
the side of the base assembly with the scres provided.
Your Dobsonian base is now completed. The adjustment knob on the base controls how easy it is
to move the base (and telescope) in the Azimuth (left/right) direction.
A
A
B
C
D
E
F
G
G
H
HH
J
I

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Locate the two Altitude bearings and install onto the sides of the
optical tube using the screws already tted in the slots on each side
of the optical tube and hex wrench provided.
The graduated scale allows you to make adjustments to balance
the optical tube (particuarly if you use any heavy accessories). Nor-
mally these should be in the centre, taking care that the bearings on
each side should be adjusted the same.
The “U-Shaped” blocks on the bearings are designed to t perfectly
into the “U-shaped” cutouts on the dosonian base. The knobs on
the altitude bearings can be used to adjust how easy it is to move
the telescope in the altitude (up/down) direction
Telescope Assembly

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Locate the nder scope and the rubber O-ring, position the O-ring in the groove on the nder
scope body.
Loosen the thumbscrew
on the “dovetail” nder
scope base on the optical
tube, and install the nd-
erscope bracket, tighten-
ing the screw to hold it in
place.
Loosen the two plastic
adjusting screws on the
nder scope base and
slide the nder scope, eye-
piece rst, into the bracket
until the O-ring seats.
Your Dobsonian telescope
is now fully asembled and
ready for nder alignment
and observing
Finderscope Assembly

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Focuser
Your telescope is equipped with a high quality Crayford type focuser that can take both 1.25 inch
and 2 inch eyepieces.
1.25 inch eyepieces are tted by loosening the
thumbscrew on the 1.25 - 2-inch adapter (A)
and installing the metal barrel of the eyepiece
into the hole (after removing all plastic dust
caps. Tighten to thumbscrew to secure the
eyepiece (do not overtighten)
To use 2 inch eypieces, loosen the thumb-
screw on the focuser (B), remove the 1.25 -
2-inch adapter and install the 2-inch eyepiece
as above but in the larger 2-inch diameter
opening.
Adjust the Tension Screw (E) so that the
eypiece/focuser moves smoothly in and out
when the focus knob (C) is turned. The Lock
Screw (F) will prevent the eypiece focussing
(ie turning the focus knobs (C & D) will not
move the focuser).
In operation, the sliver focus knob (C) will
allow you to roughly focus the eypiece, whilst the black knob (D) moves more slowly and will allow
ne focus (approximately 10:1 ratio).
Eyepieces
Your telescope is supplied with two high quality eyepieces; a 1.25” 9mm Plossl and a 2” 30mm
Superview wide angle eypiece. Calculating the magnication of an eyepiece is simple and uses
the following formula:
Power (or Magnication) = Focal length of telescope
Focal length of eyepiece
So for an Astronz 200mm Dobsonian: 1200mm/9mm = 133 and 1200mm/30mm = 40
The basic rule of thumb to remember is that an eyepiece with a larger number has a lower power
and will show a greater area of sky. When using your telescope you will generally start o󰀨 using
the lowest power eyepiece you have and switching to a higher power if required only once you
have located the object you are interested in.
A
B
C
D
F E
Using Your Telescope

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In order to use the nder scope to locate objects, it rst needs to be aligned so that objects in the
“crosshairs” of the nder are visible through the eyepiece of the main telescope.
This process is easiest during the day (though take care
not to point either the nder or the main scope anywhere
near the sun) by pointing the main telescope toward a
distant object (such as a tree, mast or power pylon).
Note the image through the eyepiece will appear invert-
ed (and at an angle). Try to get something recognisable
in the centre of the eld of view (such as the top of the
pylon in the image to the right)
Next use the nder and see if the same object is in the
centre of the eld of view.
In the case of the nder scope image to the left, the pylons is
slightly o󰀨centre (in this case the crosshairs are showing slightly
up and to the left of the image in the main eyepiece.) Correct the
alignment by adjusting the two thumbscrews on the nder until the
object is centred on the crosshairs
Once the crosshairs are perfectly over the object in the main
eyepiece, your nder scope is aligned correctly, and images in the
centre of the nder should be visible through the main eyepiece,
even at high magnications.
Finderscope Alignment

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Selecting a site
The ideal site for observing with your Astronz Dobsonian telescope, is a dark outdoor site far
away from city lights or other sources of “light pollution”. Whilst this may be impractical for most
people, try to choose a location where there is as little light as possiblle (such as street lighting,
security lighting, lights from windows etc). It’s also worth noting that heat from chimneys and
rooftops may also have a negative impact on your viewing. Don’t try observing from indoors, or
through window glass
Cooling
Until all the parts of your telescope (mirror, tube, eyepieces etc) are at the same temperature as
the surrounding ambient temperature (known as “thermal equilibrium”), even minor temperature
di󰀨erences will a󰀨ect the quility of the image.
Before viewing with your telescope, set it up in the area you plan to view for at least 30-60 min-
utes to allow all components to come to equilibrium. Using the supplied battery holder to power
the fan on the base of the mirror can help cool the mirror faster.
If the image appears distorted, hard to focus, or is rapidly moving (“boiling”), these could be
signs that your telescope needs more time to cool.
Seeing
Astronomers refer to the condition, stability and transparency of the atmosphere as “seeing”.
High altitude jet streams, turbulent air and convection currents from cooling ground objects all
cause blurring, distortion and/or scintinlation (or “twinkling”), and provide one of the biggest chal-
lenges for earth based astronomers.
If your telecope has had plenty of time to cool down, and you are still unable to get a sharp im-
age, then it is probably the atmospheric conditions (or seeing) that is to blame (particularly if the
stars are seeming to “twinkle” to the naked eye).
Often the seeing will improve later in the evening, but on occasions the only course of action is
to try again another night.
Observing

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Storing your Astronz Dobonian Telescope
For maxumim life, your telesecope should be stored in a cool, dry and dust free environment. It
is recommended that you store the optical tube (OTA) in the original box, or a purpose designed
case when not in use. The base should be stored assembled, but away from moisture.
Before packing the telescope away, ensure that it is thouroughly dry (the outside of the tube
may be gently dried with a towel or cloth, and allow to fully air dry), and that all dust covers are
in place.
Storing, particularly if assembled on the base, it is recommended that the telescope be stored
slightly “nose down” (ie with the open end pointing just below the horizontal) this will help pre-
vent dust buildup on the mirror
Cleaning and Maintenance
As your Astronz Dobsonian Telescope is a precision scientic instrument, great care should
be taken in order to maintain the optics and alignment. Cleaning of any part of the telescope
should be undertaken a little as possible.
The outside of the optical tube and base can be very gently cleaned with a soft lint-free cloth
and mild soap solution - do not use solvents on any part of the instrument,
Eyepieces can be cleaned by blowing o󰀨 dust with a bulb-type (not aerosol) air duster, or with
very gentle strokes of a camelhair brush. Fingerprints can be removed using a blotting action
with soft, white, unscented/unimpregnated tissue paper and a solution of 3-4:1 distilled water to
isopropyl alcohol. No not use photographic lens wipes/pens.
In general cleaning of the mirrors in your telescope rarely required, even if they appear to have
a lm of dust. Mirror cleaning is a specialised job as it is very easy to damage or scratch the
surface, and should be undertaken by a professional.
Storage & Maintenance

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