Celestron The G-8 11023 User manual

The G-8
Model #11023
8" OPTICAL TUBE ASSEMBLY
Model #11023-1
CG-5 EQ Mount
Model # 91515
INSTRUCTIONMANUAL

Table of Contents • i
TABLE OF CONTENTS
▲▲
▲▲
▲INTRODUCTION.................................................................................................................................... 1
How to Use this Manual ................................................................................................................. 2
A Word of Caution .......................................................................................................................... 2
The Schmidt-Cassegrain Optical System ....................................................................................... 3
▲▲
▲▲
▲ASSEMBLING YOUR G - 8 ................................................................................................................... 4
The G-8 ......................................................................................................................................... 5
Assembling the CG-5 Equatorial Mount................................................................................ 6
Setting Up the Tripod ......................................................................................................... 6
Adjusting the Tripod Height ................................................................................................ 6
Attaching the Accessory Tray ........................................................................................... 7
Attaching the Equatorial Mount ......................................................................................... 8
Attaching the R.A. Slow Motion Knob ................................................................... 9
Attaching the Declination Slow Motion Knob........................................................ 10
Attaching the Counterweight Bar and Counterweights ..........................................11
Attaching the Telescope to the Mount ..............................................................................12
Removing the Lens Cap ....................................................................................................13
Balancing the Telescope in R.A. .......................................................................................14
Balancing the Telescope in DEC ...................................................................................... 14
Adjusting the Mount in Altitude .........................................................................................15
Adjusting the Mount in Azimuth ........................................................................................15
Disassembling and Transporting Your G-8 ........................................................................16
Storing Your G-8 .............................................................................................................. 16
▲▲
▲▲
▲THE CELESTRON 8 OPTICAL TUBE ASSEMBLY ...............................................................................17
Setting Up your C8 OTA ....................................................................................................18
Installing the Finderscope ..................................................................................................18
Attaching the Finder Bracket to the Telescope ..................................................................18
Attaching the Finder to the Bracket ................................................................................... 19
Removing the Lens Cap..................................................................................................... 19
▲▲
▲▲
▲TELESCOPE BASICS .......................................................................................................................... 20
Attaching the Accessories ............................................................................................................20
The Visual Back ...............................................................................................................20
The Star Diagonal ............................................................................................................. 20
The Eyepiece ...................................................................................................................21
Image Orientation .......................................................................................................................... 22
Focusing .......................................................................................................................................23
Aligning the Finder ........................................................................................................................24
Your First Look ............................................................................................................................. 25
Daytime Observing ...........................................................................................................25
Nighttime Observing .........................................................................................................26
Calculating Magnification ...............................................................................................................27
Determining Field of View .............................................................................................................. 27
General Observing Hints ................................................................................................................28
General Photography Hints ...........................................................................................................28
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▲ ▲
▲ ASTRONOMY BASICS ........................................................................................................................29
The Celestial Coordinate System ..................................................................................................29
Motion of the Stars ........................................................................................................................30

ii •Table of Contents
Polar Alignment ............................................................................................................................. 31
Finding the Pole ............................................................................................................................32
Latitude Scales ................................................................................................................ 33
Pointing at Polaris ............................................................................................................34
Declination Drift ................................................................................................................35
Polar Alignment Finders ...................................................................................................36
Aligning the R.A. Setting Circle ........................................................................................36
▲ ▲
▲ ▲
▲ CELESTIAL OBSERVING ...................................................................................................................37
Observing the Moon ......................................................................................................................37
Observing the Planets ...................................................................................................................37
Observing the Sun .........................................................................................................................38
Observing Deep-Sky Objects .........................................................................................................39
Using the Setting Circles .................................................................................................. 39
Star Hopping ....................................................................................................................40
Viewing Conditions ........................................................................................................................42
Transparency ....................................................................................................................42
Sky Illumination ................................................................................................................42
Seeing ..............................................................................................................................42
▲ ▲
▲ ▲
▲ CELESTIAL PHOTOGRAPHY .............................................................................................................44
Short Exposure Prime Focus ........................................................................................................ 45
Piggyback .....................................................................................................................................47
Eyepiece Projection ......................................................................................................................49
Long Exposure Prime Focus .........................................................................................................51
CCD Imaging .................................................................................................................................53
Description of F-Numbers.........................................................................................................54
Imaging at f/1.95 ......................................................................................................................55
Imaging at f/6.3 ........................................................................................................................55
Imaging at f/10 .........................................................................................................................55
Imaging at f/20 .........................................................................................................................56
▲▲
▲▲
▲TELESCOPE MAINTENANCE ..............................................................................................................57
Care and Cleaning of the Optics ....................................................................................................57
Collimation ....................................................................................................................................57
▲ ▲
▲ ▲
▲ OPTIONAL ACCESSORIES ................................................................................................................. 59
▲▲
▲▲
▲THE MESSIER CATALOG....................................................................................................................64
▲▲
▲▲
▲LIST OF BRIGHT STARS ....................................................................................................................67
▲▲
▲▲
▲FOR FURTHER READING ....................................................................................................................68

Introduction •1
INTRODUCTION
Welcome to the Celestron world of amateur astronomy! For more than a
quarter of a century, Celestron has provided amateur astronomers with the
tools needed to explore the universe. The Celestron C8 is the most popular
version in our telescope line because it combines large aperture optics with
ease of use and portability. With a mirror diameter of 8 inches, your Celestron
C8 has a light gathering power of 800 times that of the unaided human eye.
Yet, the C8 optical system is extremely compact and portable despite its large
aperture because it utilizes the Schmidt-Cassegrain design. This means you
can take your C8 to the mountains, desert or wherever you observe.
The Celestron C8 is made of the highest quality materials to ensure stability
and durability. All this adds up to a telescope that gives you a lifetime of
pleasure with a minimal amount of maintenance. Furthermore, your Celestron
C8 is versatile —it will grow as your interest grows.
However, your C8 telescope is not limited to astronomical viewing alone. It can
be used as a terrestrial spotting scope to study the world around you. All you
need to do is take the time to familiarize yourself with your C8 and its basic
operation.
Your G-8 telescope (#11023) is comprised of two componets, the CG-5
equatorial mount and the 8" optical tube assembly. The first sections of this
manual covers the assembly and use of the CG-5 Eq mount and the 8" optical
tube assembly. The last sections of the manual describe how to use the G-8
telescope as a system and explores such topics as polar alignment, the
celestial coordinate system and astrophotography.
It will take a few observing sessions to familiarize yourself with your telescope,
so don't get discouraged. You should keep this manual handy until you have
fully mastered your telescope's operation.

2 •Introduction
Your G-8 telescope is designed to give you hours of fun and rewarding observa-
tions. However, there are a few things to consider before using your telescope
that will ensure your safety and protect your equipment.
WARNING ! NEVER LOOK DIRECTLY AT THE SUN WITH THE NAKED EYE OR WITH A
TELESCOPE. PERMANENT AND IRREVERSIBLE EYE DAMAGE MAY
RESULT.
NEVER USE YOUR TELESCOPE TO PROJECT AN IMAGE OF THE SUN
ONTO ANY SURFACE. INTERNAL HEAT BUILD-UP CAN DAMAGE THE
TELESCOPE AND/OR ANY ACCESSORIES ATTACHED TO IT.
NEVER USE AN EYEPIECE SOLAR FILTER OR A HERSCHEL WEDGE.
INTERNAL HEAT BUILD-UP INSIDE THE TELESCOPE CAN CAUSE THESE
DEVICES TO CRACK OR BREAK, ALLOWING UNFILTERED SUNLIGHT TO
PASS THROUGH TO THE EYE.
NEVER LEAVE THE TELESCOPE UNSUPERVISED, EITHER WHEN CHIL-
DREN ARE PRESENT OR ADULTS WHO MAY NOT BE FAMILIAR WITH
THE CORRECT OPERATING PROCEDURES OF YOUR TELESCOPE.
NEVER POINT YOUR TELESCOPE AT THE SUN UNLESS YOU HAVE THE
PROPER MYLAR SOLAR FILTER. WHEN USING YOUR TELESCOPE WITH
THE CORRECT SOLAR FILTER, ALWAYS COVER THE FINDER. AL-
THOUGH SMALL IN APERTURE, THIS INSTRUMENT HAS ENOUGH LIGHT
GATHERING POWER TO CAUSE PERMANENT AND IRREVERSIBLE EYE
DAMAGE. IN ADDITION, THE IMAGE PROJECTED BY THE FINDER IS HOT
ENOUGH TO BURN SKIN OR CLOTHING.
A telescope is an instrument that collects and focuses light. The nature of the
optical design determines how the light is focused. Some telescopes, known
as refractors, use lenses while others, known as reflectors, use mirrors. The
Schmidt-Cassegrain optical system (or Schmidt-Cass for short) uses a
combination of mirrors and lenses and is referred to as a compound or cata-
dioptric telescope. This unique design offers large diameter optics while
maintaining very short tube lengths, making them extremely portable. The
Schmidt-Cassegrain system consists of a zero power corrector plate, a
spherical primary mirror, and a secondary mirror. Once light rays enter the
optical system, they travel the length of the optical tube three times.
Inside the optical tube you will notice a black tube (not illustrated) that extends
out from the center hole in the primary mirror. This is the primary baffle tube
and it prevents stray light from passing through to the eyepiece or camera.
A Word of Caution
The Schmidt-
Cassegrain
Optical System

Introduction •3
Figure 1-1
This cross-sectional diagram shows the light path of the Schmidt-
Cassegrain optical system. Note that the light rays travel the length of
the telescope tube three times, making this a compact optical design.
Note that the curve of the corrector plate is greatly exaggerated.

4 •The G-8
ASSEMBLING YOUR G-8
AT POLARIS C
The G-8 (#11023), is the only version of the C8 that is offered on a German
equatorial mount. Like all Celestron 8 models, the G-8 uses a Schmidt-
Cassegrain optical design. The G-8 is shipped in two boxes. The first con-
tains the optical tube (i.e., telescope) and all the standard accessories, which
include:
•25mm SMA Ocular 1-1/4"
•Visual Back 1-1/4"
•Star Diagonal 1-1/4"
•6x30mm Finder and Bracket
•Lens Cap
The second box contains the tripod, equatorial mount and the hardware needed
to set it up. Included are the:
•CG-5 German Equatorial Mount
•Counterweight Bar
•Two Counterweights (3.6 Kg and 1.8 Kg)
•Declination (DEC) Slow Motion Knob
•Right Ascension (R.A.) Slow Motion Knob
•Adjustable Aluminium Tripod
•Accessory Tray
When setting up the telescope, find a large, clear area where the parts can be
laid out without fear of losing them. Start with the tripod and mount. Remove
the contents of the box and place them neatly on your work surface. Leave the
optical tube in its case until you are ready to attach it to the mount. Once
your G-8 has been unpacked and assembled, you will not need the shipping
boxes for everyday storage and transportation. However, you should save
them in case you decide to ship your telescope via a common carrier. The
foam lined footlocker for the optical tube should be kept handy for storage and
transportation.
Unpacking Your
G-8

The G-8 •5
1. Finderscope 12. Counterweight Safety Screw
2. Eyepiece 13. Counterweights
3. Star Diagonal 14. Counterweight Shaft
4. Dovetail Bar Clamp Knob 15. Counterweights shaft Lock Collar
5. R.A. Setting Circle 16. DEC Circle
6. Latitude Scale 17. DEC Lock Lever
7. Latitude Adjustment Screw 18. DEC Slow Motion Shaft
8. Azimuth Adjustment Knob 19. Dovetail Slide Bar
9. Tripod 20. Collimation Screw Cover
10. Accessory Tray 21. Corrector Plate
11. Leg Brace Assembly
Figure 2-1
The G-8
1
2
3
4
5
6
7
9
10
11
12
13
16
17
18
19
20
21
15
8
14

6 •The G-8
The tripod comes fully assembled with the metal plate, called the tripod head,
that holds the legs together at the top. In addition, the brackets that support
the accessory tray are also attached to the tripod.
Stand the tripod upright and pull the tripod legs apart until the leg brace
assembly for the accessory tray is fully extended (see figure 2-2). The tripod
will now stand by itself. To increase the stability, tighten the bolts that hold
the legs to the tripod head (use the appropriate size wrench from the supplied
set). This will help minimize any flexure or wobble of the legs.
Once the tripod is set up, you can adjust the height at which it stands. To do
this:
1. Loosen the knob on the leg clamp so that the tripod leg can be adjusted.
2. Slide the center portion of the tripod leg away from the tripod head until it
is at the desired height.
3. Tighten the knobs on each leg clamp to hold the legs in place.
Setting Up the Tripod
Adjusting the Tripod
Height
Figure 2-2
Setting up the tripod requires nothing more than pulling the tripod legs away from the
tripod head. The height at which the tripod stands can be adjusted by sliding the slats
in the center of each leg toward or away from the tripod head.
Assembling the CG-5 Equatorial Mount (#91515)

The G-8 •7
With the tripod set up, you are ready to attach the accessory tray to the tripod.
There are three wing bolts that hold the accessory tray to the bracket.
1. Locate the three wing bolts.
2. Place the accessory tray over the bracket and position it so the thread
holes in the accessory tray are above the slotted holes in the bracket.
3. Insert the wing bolts up through the slotted holes in the bracket (see figure
2-3).
4. Thread the wing bolts into the holes in the accessory tray.
5. Tighten the wing bolts fully.
With the accessory tray in place, the tripod will be much more stable making it
easier to attach the mount and telescope.
Attachingthe Accessory
Tray
Figure 2-3

8 •The G-8
The equatorial mount allows you to tilt the telescope’s axis of rotation so that
you can track the stars as they move across the sky. The CG-5 mount is a
German equatorial mount that attaches to the tripod head (i.e., metal plate on
the tripod). On one side of the plate there is an “N”which signifies north. This
side of the tripod will face north when setting up for an astronomical observing
session. Above the “N”is a peg about 3/4" high that points straight up. To
attach the equatorial head:
1. Locate the azimuth adjustment screws on the equatorial mount.
2. Retract the screws so they no longer extend into the azimuth housing
(rectangular extrusion) on the mount. Do NOT remove the screws since
they are needed later for polar alignment.
3. Hold the equatorial mount over the tripod head so that the azimuth housing
is above the metal peg.
4. Place the equatorial mount on the tripod head so that the two are flush.
5. Tighten the knob on the underside of the tripod head to hold the equatorial
mount firmly in place. The knob is already attached and can NOT be
removed.
Attaching the Equatorial
Mount
Figure 2-4

The G-8 •9
Attaching the R.A. Slow Motion Knob
With the mount securely in place, you are ready to attach some of the acces-
sories (the telescope tube will be added last). Start with the Right Ascension
(R.A.) slow motion knob. The R.A. slow motion knob allows you to make fine
pointing adjustments in the direction the telescope is aiming (once it is
attached to the mount). To install the knob:
1. Locate the hard plastic shell under the R.A. shafts.
2. Remove either of the two oval tabs by pulling tightly.
3. Line up the flat area on the inner portion of the R.A. slow motion knob with
the flat area on the R.A. shaft (see figure 2-5).
4. Slide the R.A. slow motion knob onto the R.A. shaft.
The knob is a tension fit, so sliding it on holds it in place. As mentioned
above, there are two R.A. shafts, one on either side of the mount. It makes no
difference which shaft you use since both work the same. Use whichever one
you find more convenient. If, after a few observing sessions, you find the R.A.
slow motion knob is more accessible from the other side, pull firmly to remove
the knob, then install it on the opposite side.
Figure 2-5

10 •The G-8
Attaching the Declination Slow Motion Knob
Like the R.A. slow motion knob, the DEC slow motion knob allows you to
make fine pointing adjustments in the direction the telescope is pointed.
The DEC slow motion knob attaches in the same manner as the R.A. knob.
The shaft that the DEC slow motion knob fits over is toward the top of the
mount, just below the telescope mounting platform. Once again, you have two
shafts to choose from. Use the shaft that is pointing toward the ground. This
makes it easy to reach while looking through the telescope, something which
is quite important when you are observing.
1. Line up the flat area on the inner portion of the DEC slow motion knob with
the flat area on the DEC shaft.
2. Slide the DEC slow motion knob over the DEC shaft (see figure 2-6).
Figure 2-6

The G-8 •11
Attaching the Counterweight Bar and Counterweights
The last item to be mounted before the telescope tube is the counterweight bar
and counterweights. Used to balanced the telescope, the counterweight bar
attaches to the opposite side of the mount as the telescope. To install the
counterweight bar:
1. Retract the counterweight bar lock nut by turning it counterclockwise. This
will expose the threads on the end of the counterweight bar.
2. Thread the counterweight bar into the mount completely. Once again, it
threads into the mount opposite the telescope (see figure 2-7).
3. Tighten the counterweight bar lock nut fully for added support.
The counterweight bar is now installed. With the counterweight bar in place,
you are ready to attach the counterweights.
1. Lock the DEC clamp to hold the mount in place.
2. Remove the safety thumbscrew on the end of the counterweight bar.
3. Loosen the set screw on the counterweight itself so that the central hole of
the counterweight is unobstructed.
4. Slide the counterweight onto the counterweight bar. Move it high enough
to allow room for the second weight (see figure 2-7).
5. Tighten the set screw on the counterweight to hold it in position.
6. Repeat this process for the second weight.
7. Replace the safety thumbscrew on the end of the counterweight bar. The
thumbscrew will prevent the counterweights from sliding off the bar should
they ever become loose.
Figure 2-7

12 •The G-8
With the mount fully assembled, you are ready to attach the telescope to the
mount.
•Before you attach the optical tube, fully tighten the right ascension and
declination clamps. This will prevent the telescope from moving
suddenly once attached to the mount.
1. Loosen the hand knob on the side of the CG-5 mount.
2. Slide the dovetail bar that is attached to the telescope onto the CG-5
mount (see figure 2-8).
3. Tighten the knob on the CG-5 mount to hold the telescope in place.
NOTE: Never loosen any of the knobs on the telescope tube or mount. Also, be sure
that the corrector end of the telescope is pointing away from the ground at all
times.
Attaching the Telescope
to the Mount
Figure 2-8
This illustration shows the correct mounting procedure for the optical tube onto the CG-5
mount. The dovetail slide bar has been attached to the telescope tube and is ready to
attach to the CG-5 mount.

The G-8 • 13
The G-8 lens cap utilizes a bayonet-type locking mechanism to hold it in
place. To remove the lens cap, hold the cover firmly and rotate the outer edge
1/2”counterclockwiseandpull off.
To eliminate undue stress on the mount, the telescope should be properly
balanced around the polar axis. In addition, proper balancing is crucial for
accurate tracking if using an optional motor drive. To balance the mount:
1. Release the R.A. Clamp and position the telescope off to one side of the
mount (make sure that the balance bracket thumbscrew is tight). The
counterweightbar will extend horizontally on the oppositeside of the
mount (see figure 2-9).
2. Release the telescope — GRADUALLY — to see which way the telescope
“rolls.”
3. Loosen the set screw on one or both counterweights.
4. Move the counterweights to a point where they balance the telescope (i.e.,
it remains stationary when the R.A. clamp is released).
5. Tighten the set screw to hold the counterweight(s) in place.
These are general balance instructions and will reduce undue stress on the
mount. When taking astrophotographs, this balance process should be done
for the specific area at which the telescope is pointing.
Removing the Lens Cap
Figure 2-9Figure 2-9
Figure 2-9Figure 2-9
Figure 2-9
The telescope should be balanced after all the standard accessories (i.e., star diagonal,
eyepiece, etc.) have been attached to the telescope. The correct procedure for attaching
these accessories is discussed in the section on “Telescope Basics.”
Balancing the Telescope
inR.A.
R.A. CLAMP

14 • The G-8
The telescope should also be balanced on the declination axis to prevent any
sudden motions when the DEC clamp is released. To balance the telescope in
DEC:
1. Release the R.A. clamp and rotate the telescope so that it is on one side
of the mount (i.e., as described in the previous section on balancing the
telescope in R.A.).
2. Lock the R.A. clamp to hold the telescope in place.
3. Release the DEC clamp and rotate the telescope until the tube is parallel
to the ground (see figure 2-10).
4. Release the tube — GRADUALLY — to see which way it rotates around
the declination axis. DO NOT LET GO OF THE TELESCOPE TUBE
COMPLETELY!
5. Slightly loosen the balance bracket thumbscrew and slide the telescope
eitherforwardorbackward until it remains stationary when the DEC clamp
is released. Do NOT let go of the telescope tube while the balance
bracket thumbscrew is loose.
6. Tighten the thumbscrew firmly to hold the telescope in place.
Like the R.A. balance, these are general balance instructions and will reduce
undue stress on the mount. When taking astrophotographs, this balance
process should be done for the specific area at which the telescope is pointing.
Balancing the Telescope
in DEC
Figure 2-10Figure 2-10
Figure 2-10Figure 2-10
Figure 2-10
As with R.A., the telescope should be balanced in DEC after all the standard accessories
(i.e., star diagonal, eyepiece, etc.) have been attached to the telescope.

The G-8 • 15
For the purpose of polar alignment, there are two directions in which the mount
can be adjusted; vertically, which is called altitude and horizontally, which is
called azimuth. There are several ways to align on the celestial pole, many of
which are discussed later in this manual. This section simply covers the
correct movement of the mount during the polar alignment process. To adjust
the mount in altitude (i.e., raise or lower the angle of the polar axis), turn the
altitudeadjustmentscrew:
• Turning the knob clockwise increases the angle at which the polar axis is
pointing
• Turning the handle counterclockwise lowers the angle at which the polar
axis is pointing.
The latitude adjustment on the CG-5 mount has a range of 40°, starting at 20°
going up to 60°.
For rough adjustments in azimuth, simply pick up the telescope and tripod and
move it. For fine adjustments in azimuth:
1. Turn the azimuth adjustment screws located on either side of the azimuth
housing. While standing behind the telescope, the knobs are on the front
ofthe mount.
•Turningtheright adjustment knob clockwise moves the mount toward the
right.
• Turning the left adjustment knob clockwise moves the mount to the left.
Both screws push off of the peg on the tripod head, which means you may
have to loosen one screw while tightening the other. The screw that holds the
equatorial mount to the tripod may have to be loosened slightly.
Adjusting the Mount
inAltitude
Adjusting the Mount
inAzimuth
Figure 2-11Figure 2-11
Figure 2-11Figure 2-11
Figure 2-11

16 • The G-8
The entire telescope and mount is light enough to pick up and carry outside for
a casual observing session. If, however, you want to transport your G-8 to a
remote observing location, you must partially disassemble it. Here’s how:
1. Remove the telescope from the equatorial mount. Return it to the shipping
carton to ensure safe transportation.
2. Remove the three wing bolts that hold the accessory tray to the tripod.
3. Pull the accessory tray off the bracket.
4. Thread the wing bolts back onto the accessory tray once they are removed
from the bracket. This will eliminate the possibility of losing them.
5. Fold the tripod legs together and you are ready to transport your G-8
telescope.
The equatorial mount does NOT have to be removed if you are transporting the
telescopeyourself. However, you may want to removethe counterweights from
thecounterweight bar to lighten the mount.
If you are shipping the telescope via a common carrier, you should completely
disassemble the telescope and return all parts to their original shipping
container.
When not in use, your Celestron G-8 can be left fully assembled and set up.
However, all lens and eyepiece covers should be put back in place. The
opening to the rear cell must also be covered. This will reduce the amount of
dust build-up on the optical surfaces and reduce the number of times you need
to clean the instrument. You may want to return everything to its original
shipping container and store all the parts there. If this is the case, all optical
surfacesshould still be covered to preventdust build-up.
Now that you have completed assembling your G-8, you are ready to begin
attaching the accessories. Please turn to the section on “Telescope Basics”
formoreinformation.
Disassembling and
Transporting Your
G-8
Storing Your G-8
What Next?

The C8 Optical Tube Assembly •17
THE 8" OPTICAL TUBE ASSEMBLY (#11023-1)
The Celestron 8 Optical Tube Assembly (OTA) is simply the telescope without
an equatorial mount and clock drive unit. In its standard configuration, the C8
Optical Tube Assembly is designed to attach to a standard, but very rigid,
photographic tripod for terrestrial viewing. However, this does not mean that
the C8 Optical Tube Assembly can not be used for astronomical viewing. It
can also be used with your own heavy duty German equatorial mount or it can
be used as an altazimuth telescope for casual astronomical observations. The
C8 Optical Tube Assembly (11023-1) is shipped in one carton which contains
the telescope and all standard accessories which include:
•25mm SMA Ocular 1-1/4"
•Visual Back 1-1/4"
•Star Diagonal 1-1/4"
•6x30mm Finder and Bracket
•Balance Bracket (for tripod adaption) - Dovetail Slide Bar
•Lens Cap
Figure 3-1