ASTRO-PHYSICS GTOCP3 User manual
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ASTRO-PHYSICS
1200 GERMAN EQUATORIAL WITH
GTO SERVO MOTOR DRIVE
MODEL 1200GTO PARTS LIST – MODEL GTOCP3 5
FEATURES AND SPECIFICATIONS 5
INTRODUCTION 6
Why Polar Alignment is Important 6
Compensation for the Earth’s rotation 6
ASSEMBLY DIAGRAM 7
BEFORE YOU LEAVE HOME 7
BEFORE YOU LEAVE HOME 8
Gross Latitude Adjustment 8
Attach Pier Adapter to Pier Post (purchased separately) 9
1200 Standard Pier Adapter (part # 1200SPA) 9
1200 Rotating Pier Adapter with Azimuth Bearing (part # 1200RPA) 9
AT YOUR OBSERVING SITE 10
Assemble Pier (purchased separately) 10
Assemble Polar Axis Assembly to Pier or Tripod 10
Polar Alignment 10
Rough Polar Alignment 10
Fine Polar Alignment 11
Methods for fine polar alignment 11
Azimuth Adjustments 12
Rotating Pier Adapter with Azimuth Bearing (1200RPA) 12
Standard Pier Adapter (1200SPA) 12
Altitude Adjustment 12
Tips for Adjusting the Altitude 13
Assemble Declination Axis 14
Removing Declination Axis at the End of your Observing Session 14
Attach Mounting Plate (purchased separately) 15
Understanding the R.A. and Dec. Clutch Knobs 16
Attach Counterweight Shaft and Counterweights 16
Attach Mounting Rings and Scope (purchased separately) 17
Balancing Your Telescope 17
Fine Polar Alignment 17
SERVO MOTOR DRIVE 18
GTO Control Box – Model GTOCP3 18
R.A. and Dec. Cable Connections 18
12V Connector 18
POWER Indicator Light 19
KEYPAD Connector 19
RS-232 Connectors 19
FOCUS Connector 19
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RETICLE Connector 19
AUTOGUIDER Connector 19
+6V Connector 19
N and S Switch 20
Removing the GTO Control Box From 1200 Mount 20
GTO KEYPAD OPERATION 20
PULSEGUIDE BY SIRIUS-IMAGING 20
CABLE MANAGEMENT 21
1200 Motor Cables 21
Accessory Cables 21
Example from International Space Station – Amateur Telescope (ISS-AT) Project 21
SLEWING YOUR MOUNT IN BELOW FREEZING TEMPERATURES 23
MOUNT CARE AND ALIGNMENT 24
Mount Maintenance 24
Tips and support 24
TROUBLESHOOTING 24
INSTALLATION OF ENCODERS AND ENCODER HOUSINGS -1200 MOUNT 26
Fitting Declination Encoder Housing 26
Fitting Right Ascension Encoder Housing 27
Periodic Maintenance 27
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ASTRO-PHYSICS
1200 GERMAN EQUATORIAL WITH
GTO SERVO MOTOR DRIVE
MODEL 1200GTO PARTS LIST – MODEL GTOCP3
1 Polar axis assembly (right ascension-R.A.) with Servo Box GTOCP3
1 Declination (Dec.) axis assembly
1 18.5” Stainless counterweight shaft (1.875” dia.) with washer stop and black plastic knob (knob has 5/16 thread)
1 Y cable – R.A. portion is 12.5” long and Dec portion is 37.5” long
1 D.C. power cord (cigarette lighter adapter on one end) - 8’ long
1 GTO Keypad controller with 15’ coiled cable
1 Keypad Protector (KEYPRO)
1 Hex key set
2 8-32 thumbscrews (substitute these for 8-32 set screws that hold GTO Servo Control Box in place, if you wish)
1 PulseGuide software by Sirius-Imaging on CD
In order to fully assemble your mount, you will need the following items sold separately: pier adapter (either standard or
rotating), mounting plate, 10” O.D. pier, counterweights and portable rechargeable battery pack (or 110 to 12V DC
converter). Several sizes and types are available for your selection. Many of these items will be discussed throughout
these instructions.
Several additional options are available:
28” counterweight shaft – 27” useable length, part # M12661-A
Santa Barbara Instrument Group CCD Imaging cameras and ST-4 Autoguider or STV - if you plan to pursue CCD
imaging or astrophotography
Pier accessory trays for 10” pier and support bars - handy to keep your eyepieces close at hand
Polar axis telescope - threads into the base of the polar axis assembly. Many users find a polar axis telescope useful for
zeroing in on the pole quickly, particularly with telescopes that are not orthogonal to the mount.
Mounted encoders – Although you can use these with your mount, they are not necessary since the go-to functions of
the mount are more accurate. The 4000 steps of the encoders, which read the position of the shaft are very
coarse (324 arc seconds) while the encoder that is built into the servo motor itself is 0.05 arc seconds.
FEATURES AND SPECIFICATIONS
R.A. worm wheel: 10.3”, 225-tooth aluminum
Dec worm wheel: 7.2”, 225-tooth aluminum
Worm gear: Brass
R.A. shaft: 3.35” diameter
R.A. thrust bearings: 9.5” diameter
Dec shaft: 2.36” diameter
Dec thrust bearings: 6.5” diameter
Counterweight shaft: 18.5” useable length, 1.875” diameter, stainless steel, removable
Latitude range: 21.5 - 68 degrees with or without polar scope or encoders attached
Azimuth adjustment: Approximately 14 degrees
Setting circles: Porter Slip Ring design, engraved
Right ascension: 4-minute increments, pointer
Declination: 1-degree increments, pointer
Motors: Zero-cogging servo motors
Power Consumption: 0.4 amps at the sidereal rate
3 amps both motors slewing
Power requirements: 12 VDC, range 11.5 to 18V (higher voltage recommended for very cold temps and heavy loads)
Weight of mount: Equatorial head: 81 lbs. (36.7 kg)
Dec axis: 31 lbs. (14.1 kg)
R.A axis: 50 lbs. (22.7 kg)
Counterweight shaft: 14 lbs. (6.4 kg)
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INTRODUCTION
The 1200 German equatorial was designed to meet the needs of the advanced observer who requires a mount with
maximum strength and rigidity and minimum weight. The excess material in both axes has been carved out while retaining a
heavily ribbed structure for internal strength and rigidity. A unique dovetail was machined into the mating surfaces of the
R.A. and Dec axes. This feature allows quick and easy assembly in the field without any tools.
The DC servo motor drive with GTO computer system, including the keypad controller with its digital display screen and
PulseGuide software offer extraordinary sophistication for today’s observer. Whether you enjoy visual astronomy exclusively
or plan an aggressive astrophotography or CCD imaging program, this mount will allow you to maximize your night out
under the stars.
The advanced keypad features allow you to slew automatically to objects in a wide range of databases as well as any
RA/Dec or Alt/Az coordinate. A large selection of common names for stars and other objects makes your selection a snap.
The rapid slew rate of 5 degrees per second (1200x) allows you to locate objects very quickly and accurately. You will be
very pleased with the intuitive operation of this controller. There are no complicated sequences of keystrokes to remember.
It is so easy to use that even it you don’t use it for a few months, you will feel at home with the keypad very quickly.
The 1200 is equally at home in a permanent observatory or as a portable mounting for remote star parties thanks to the
ease with which the two axes come apart. This is the perfect mount for a large refractor, Newtonian, Cassegrain or
astrograph.
In order to maximize your pleasure on your first night out, we recommend that you familiarize yourself with the assembly
and basic operation of the mount indoors. The temperature will be comfortable, the mosquitoes at bay, and you'll have
enough light to see the illustrations and read the manual. Please take particular note of counterbalancing, use of the
clutches and operation of the keypad controller.
Why Polar Alignment is Important
Compensation for the Earth’s rotation
If you were to take a long exposure photograph with
Polaris (often called the north star) in the center of the
field, you would discover that all stars seem to revolve
around Polaris. This effect is due to the rotation of the
earth on its axis. Motor driven equatorial mounts were
designed to compensate for the earth's rotation by moving
the telescope at the same rate and opposite to the earth's
rotation. When the polar axis of the telescope is pointed at
the celestial pole (polar aligned) as shown in Diagram 1,
the mount will follow (track) the motions of the sun, moon,
planets and stars. As a result, the object that you are
observing will appear motionless as you observe through
the eyepiece or take astrophotos.
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ASSEMBLY DIAGRAM
Please read all instructions before attempting to set up your 1200 mount. The Model 1200 is very rugged, however like any
precision instrument, it can be damaged by improper use and handling. Please refer to Diagram 2 for an illustration of the
mount. The parts are labeled so that we can establish common terminology.
The following terms and abbreviations are used interchangeably in these instructions:
polar axis = right ascension axis = R.A. axis = R.A. housing
declination axis = dec. axis = dec. housing
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BEFORE YOU LEAVE HOME
Since most of us must set up our instruments in the dark, in the cold or while battling mosquitoes, a bit of pre-planning and
organization is important. There are few simple things that can be accomplished in the comfort of your home before heading
outside.
Gross Latitude Adjustment
The total latitude range of the 1200 mount is
approximately 21.5-68 degrees with 4 adjustment
positions. Since most astronomers typically observe within
one latitude range, this adjustment is made just once, if at
all. Prior to shipment, we preset the mount to your latitude
range for your convenience. If you travel to another
observing location, determine the latitude of your
observing site and make the appropriate adjustment.
The four positions for the altitude adjustments have the
following approximate ranges:
55 degrees to 68 degrees latitude - top position
37 degrees to 59 degrees latitude - third position
28 degrees to 50 degrees latitude - second position
21.5 degrees to 37 degrees latitude - bottom position
How to change the position of the altitude adjuster bar
1. Use only the R.A. axis. DO NOT attempt the make
these adjustments with the declination axis in place and
certainly not with an instrument fully mounted.
2. Loosen both altitude-locking knobs about 1 turn.
3. Locate the side of the polar axis that does not have the
motor/gear housing box. Loosen (about 1 turn) the
polar axis pivot screw and altitude adjuster bar fixing
screws on this side only. With your hand, push the
polar axis upwards so that the altitude locking knobs
are positioned at the top of the altitude slot (this is the
maximum altitude position). Some resistance will be felt
with this operation since you are pushing against the
weight of the polar housing and the resistance of the
remaining polar axis pivot screw (which has not been
loosened).
4. Before attempting to move the altitude adjuster bar, you
must tighten the altitude-locking knob on the motor/gear housing side.
This will prevent any downward movement of the polar axis during
positioning of the altitude adjuster bar.
5. While supporting the altitude adjuster bar, remove the two screws that
support it on each side (4 screws in all), but keep the two ends of the bar
in contact with the side of the mount, don't remove it completely (this tip
is for your convenience).
6. Determine the latitude range that you need (refer to Diagram 3) and
position the hole that is marked “A” in Diagram 5 at that location. Note
that this hole is located at the rounded part of the altitude bar.
7. Attach two of the screws (one on either side of the adjuster bar), but do
not tighten. Rotate the altitude adjuster bar around this pivot point until
one of the other holes lines up. Insert the remaining two screws. Lightly
tighten so that you still have some ability to move the bar.
8. Note that the altitude adjustment knob is attached to a threaded rod that
travels through the altitude adjuster bar. Turn the knob so that the
altitude adjuster bar is positioned approximately in the middle of the threaded rod. You should see about half of
the threaded rod protruding from both sides of the altitude adjuster bar. This will allow you to move the mount fully
within the altitude range.
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9. At the end of the threaded rod mentioned in the last step, you will see a small brass altitude adjuster thrust pad.
This is the part that will come in contact with the polar axis as you ease it back into position. Loosen the altitude
locking knob (motor/gear side) and lower the polar axis so that it rests comfortably on this pad. The threaded rod
should be positioned at a right angle to the polar axis housing. Firmly tighten the altitude adjustment screws.
10. Turn the altitude adjustment knob to raise or lower the polar axis to your approximate observing latitude. Tighten
the altitude locking knobs with finger pressure only. You do not need to tighten with the hex key.
11. Firmly tighten both polar axis pivot screws with the hex key.
Attach Pier Adapter to Pier Post (purchased separately)
If you purchased the pier from Astro-Physics, the pier adapter of the 1200 may be already attached to the top of the pier. If
you are constructing your own pier or tripod, you will need to incorporate this part. Two models of the pier adapter are now
available for use with the 1200 from Astro-Physics. If you have more than one pier, you may wish to purchase two adapters
so that you can leave them attached permanently. These pier adapters can be used with prior versions of the 1200 mount.
1200 Standard Pier Adapter (part # 1200SPA)
The Standard Pier Adapter includes the machined flat plate, four machined aluminum lock
knobs with stainless washers, the azimuth adjuster block, six 5/16”-18 x 5/8” side bolts and
washers. All machined parts are black anodized. The Standard Pier Adapter was designed
to fit into a 10" x 0.094" wall tube with 6 screws threaded into the side or bolted onto a flat
surface by using the four countersunk thru-holes (pier adapters from early production runs may
not have the thru-holes).
1200 Rotating Pier Adapter with Azimuth Bearing (part # 1200RPA)
The Rotating Pier Adapter rotates on a bearing surface for ultra-smooth operation. It
includes a machined flat plate assembly with four machined aluminum lock knobs and
stainless washers, the azimuth adjuster block and six 5/16”-18 x 5/8” side bolts with
washers. This adapter allows you to lock the mount down with no need to loosen the base
during azimuth adjustment. Observers who use the 1200 as a portable mount and set up
frequently will find this especially useful. Unlike the standard pier adapter, the rotating pier
adapter cannot be bolted to a flat surface without an adapter.
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AT YOUR OBSERVING SITE
Assemble Pier (purchased separately)
Begin by assembling the portable pier at the desired observing
location. Take note which direction is north.
1. Slide the three legs onto the nubs of the base and
rotate the assembly so that one of the legs points
toward north (or south, if that is your preference).
2. Place the pier post on the base orienting the center
azimuth block directly north. If you choose to have
one leg north, then the pier adapter plate will have to
be installed with the azimuth block directly over a
turnbuckle. If you have one leg south, the pier adapter
plate will have to be installed with the azimuth block
over and between two of the pier post turnbuckles.
3. Attach the tension rods. The turnbuckles should be
drawn tight until the whole assembly is stiff enough to
support your weight without movement.
Assemble Polar Axis Assembly to Pier or Tripod
In order to track the motion of astronomical objects, the polar axis must be positioned so that an imaginary line drawn
through the center of the axis points toward the celestial pole. Refer to the diagram at the front of this manual for a graphical
representation. At this stage of the assembly process, you want to position the mount so that it points roughly north.
1. Remove the four (4) hand knobs on either the Standard or Rotating Pier Adapter and keep them close at hand.
2. Prior to lifting the polar axis assembly into place, turn the fine azimuth adjustment knobs so that the space
between them is wide enough to allow the center azimuth block to fit easily between them. Ensure both pier top
and polar axis assembly mating surfaces are clean and free of dirt.
3. Place the polar axis assembly onto the pier top adapter so that the center azimuth block fits between the fine
azimuth adjustment knobs.
4. Move the base of the polar axis assembly so that the threaded holes of the pier top can be seen through each of
the four slots.
5. Thread the four hand knobs loosely in place (you will tighten these later after polar alignment) with the washers
underneath. If you are using the Standard Pier Adapter, be sure that the side with the rounded edge is facing
down. This will ensure smooth movements as you adjust your polar alignment. The position of the washers does
not matter for the Rotating Pier Adapter.
Polar Alignment
We recommend that you accomplish your polar alignment in two phases – rough alignment and fine alignment.
Rough Polar Alignment
For rough polar alignment, your goal is to sight the celestial pole when looking through the polar alignment sight hole in the
center of the polar axis. You will need to make altitude (up/down) and azimuth (side-to-side) adjustments to the position of
the mount.
We recommend that you do your rough polar alignment with the R.A. axis only since you will be making major adjustments
to the position of the mount at this time. The remainder of the mount, telescope and counterweights would add considerable
weight and require more hand effort. Later, you will do your final polar alignment with the telescope and counterweights
attached, but the adjustments will be small.
1. Remove the RA axis rear cover (or RA encoder housing if it is installed – please refer to the section of this manual
entitled “ Installation of Encoders and Encoder Housings – 1200 Mount“). Alternatively, you can simply sight up the
side of the polar axis to see Polaris.
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2. If you examine the polar axis assembly, you will see that the center of the R.A. shaft is hollow.
NOTE: If you have already attached the Dec. axis, remove the sight hole cover and rotate the internal Dec. shaft by
moving the top of the Dec. axis (or the cradle plate if it is attached) to reveal the sight hole that has been drilled into it.
Now, you can look through the shaft to the other side.
3. Move the entire pier or tripod east or west until the mount is oriented approximately towards the pole (an imaginary line
drawn through the hollow shaft).
4. Azimuth adjustments: Use the two fine azimuth adjustment knobs, one on each side of the mount, to make
adjustments. You must back off the opposing azimuth knob in order to move the other knob in that direction. Please
refer to Diagram 4. Refer to the Azimuth Adjustments section below for information pertaining to the Rotating Pier
Adapter and Standard Pier Adapter. The procedures are different depending on which one you are using.
Altitude (latitude) adjustments: Loosen the altitude locking knobs. Move the polar axis up or down with the large
altitude adjustment knob located in the front of the polar axis assembly. The tommy bar can be positioned in any of the
threaded holes located in the altitude adjustment knob. Use this bar to help you turn the knob. Please refer to
Diagrams 3 and 4. We have found that fine altitude adjustments also can be made using the turnbuckle on the north
leg of our pier, if used.
One turn of the altitude knob is approximately 0.5 degrees (30 arc minutes).
5. Continue your azimuth and altitude adjustments until you can sight Polaris in the polar alignment sight hole. At this
point, you have achieved rough polar alignment, which may be sufficient for casual visual observations if you are not
planning to use go-to functions, i.e. slew to target objects with the keypad or planetarium program. When the R.A.
motor is engaged, it will compensate for the rotation of the earth and keep the target object within the eyepiece field of
view. Your target object will slowly drift since polar alignment at this stage is only approximate. However, you can
make corrections with your keypad as we will discuss later.
6. Altitude: Tighten the altitude locking knobs by hand.
7. Azimuth:
a) Standard Pier Adapter: Tighten the pier knobs firmly by hand.
b) Rotating Pier Adapter: No further tightening required.
Fine Polar Alignment
If you plan to use any of the go-to functions of the 1200GTO or do astrophotography, you must polar align. Procedures will
be discussed here, however you will complete this alignment when your scope and other equipment are mounted.
Methods for fine polar alignment
• Polar Alignment Scope – Our optional polar scope (PASILL3 or earlier models) will allow you to quickly align your
mount on the pole stars. The reticle was designed for use in both the Northern and Southern hemispheres. Even
users of the GTO computerized mounts will find these polar scopes useful, particularly if your telescope is not
orthogonal to the mount (please refer to the keypad manual for a discussion of orthogonality). If you have a polar
alignment scope, please read the instructions sheets that come with it. If you are planning long exposure
astrophotos or imaging, we suggest that you use the polar axis telescope, then tweak the final polar alignment by
another means, perhaps CCDOPS from SBIG or other similar alignment program.
• GTO Keypad – Please refer to the instruction manual for the GTO Keypad and read the section describing the
startup sequence and various polar alignment procedures including a procedure you can do in the daytime.
• CCDOPS - We suggest that you refer to detailed instructions in the GTO Keypad manual for a method that utilizes
CCDOPS from Santa Barbara Instrument Group (SBIG) for precise polar alignment. There are also other similar
alignment procedures, including one in MAXIM DL from Diffraction Limited.
• Star Drift method – Traditionally, this has been regarded as the most accurate method of polar alignment.
However, if you are using the old method of drift alignment (star near eastern horizon, etc), you are doomed to
failure. To obtain more accurate results, choose stars somewhere near the celestial equator due south or slightly
east and west, but not below 45 degrees elevation. If you attempt to drift align below that, you will encounter
atmospheric refraction, which skews your alignment.
• JMI Digital Setting Circles – Please read the instructions included with your JMI unit. You must have the encoders
installed on your 1200 mount (part #1200ENC). Refer to the section of this manual entitled “Installation of
Encoders and Encoder Housings –1200 Mount. Keep in mind that the encoder resolution of Digital Setting Circles
is much coarser. Therefore, this is the least accurate method.
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• Members of the ap-gto Yahoo group occasionally discuss alternative methods of polar alignment that they have
found helpful. We suggest that you participate in this Internet discussion group. Follow the links from the sidebar of
our website to find the group.
Azimuth Adjustments
The one-piece Azimuth Adjustment assembly makes for easy and accurate polar alignment in your observatory or in the
field. The heavy-duty construction and integrated one-piece design results in smooth control of the azimuth axis. Large left
and right adjuster knobs are graduated for precise control of azimuth position angle. The small graduations are 1.3 arc
minutes per graduation; long graduations are 6.5 arc minutes per graduation. The size of the knobs makes them easy
to turn with very little torque required, even with the mount fully loaded.
The procedure for making azimuth adjustments is somewhat different with the Rotating Pier Adapter (1200RPA) and
Standard Pier Adapter (1200SPA). If you are using your own pier adapter or one provided with the Particle Wave
Technologies Monolith Pier, there may be additional considerations to achieve smooth, accurate adjustments.
Rotating Pier Adapter with Azimuth Bearing (1200RPA)
The rotating pier adapter consists of two plates that allow ultra-smooth adjustments for critical polar alignment. When using
the Rotating Pier Adapter, tighten the hand knobs fully by hand. It is not necessary to use a wrench. These will remain tight
during and after the adjustment procedure.
Notice the two setscrews on the side of the rotating pier adapter. These setscrews are used to apply tension to the rotating
plate. You may need to adjust these setscrews to gain the proper feel during the adjustment process. If you notice a slight
amount of shift, particularly with a larger scope, tighten the screws. If you find too much resistance, the screws may need to
be loosened slightly.
Azimuth adjustment is accomplished with the two fine azimuth adjustment knobs, one on each side of the mount. You must
back off the opposing azimuth knob in order to move the other knob in that direction. Please refer to Diagram 4. Follow one
of the alignment methods discussed above in the Polar Alignment section.
Once your azimuth position has been attained, do not tighten the hand knobs any further since this is likely to disturb your
alignment.
Standard Pier Adapter (1200SPA)
Each of the azimuth lockdown knobs has a hardened washer. With these washers, the lockdown knobs can hold the mount
down tight while still allowing the axis to be easily adjusted with your fingers. These will eliminate minor shifts in the axis
when you are tweaking your azimuth adjustment.
The washers have a sharp-edged side and a rounded-edge side (the difference is subtle). Place them with the sharp edge
of the washers facing up toward the knob, rounded edge down onto the painted surface of the base plate. If you install the
washers with the sharp edge down, they will bind into the paint and prevent smooth movement. If you do not have a
permanent installation, you may wish to mark the down (or up) side of the washer with a marker so that you can quickly
identify the desired orientation. If you have a rotating pier plate, the orientation of the washers is not important at all.
1. The altitude axis should be fully locked down with a hex key before adjusting the azimuth.
2. Follow one of the methods of polar alignment mentioned above.
3. During the initial adjustment phase, the 4 lock-down knobs should be hand tight only. This will allow easy
movement of the azimuth axis.
4. When you are close to the final position of the azimuth axis, use a hex key to lock down the rear knob only. The
azimuth can still be moved with the adjusters, but it will now be solidly connected to the pier top. The other knobs
should remain hand-tight. The weight of the mount and scope puts pressure on the front of the plate for a solid
connection, so it is not necessary to lock them down fully with a hex key.
Altitude Adjustment
Loosen the altitude locking knobs. Move the polar axis up or down with the large altitude adjustment knob located in the
front of the polar axis assembly. The tommy bar can be positioned in any of the threaded holes located in the altitude
adjustment knob. Use this bar to help you turn the knob. Please refer to Diagrams 3 and 4 if you are unsure about these
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parts. It is also possible to make fine altitude adjustments by using the turnbuckle on the north leg of our pier, if used.
One turn of the altitude knob is approximately 0.5 degrees (30 arc minutes).
Tips for Adjusting the Altitude
The mount's polar axis is held in place between the two side plates. It is possible for the mount to shift slightly when the side
bolts are fully tightened down after adjustment of the altitude angle. To prevent that, it is suggested that the initial altitude
adjustment be done with these bolts hand tight, and as you approach the final adjustment point, tighten the bolts with a hex
key after each movement. If you move the axis too high and overshoot the angle, it is better to loosen the two bolts a bit,
bring the axis back down a very small amount and progress back up with the bolts hand tight. This way you are using the
weight of the mount to insure a solid connection to the altitude adjuster. During the final adjustment phase, screw the
Tommy bar into one of the holes in the knob. This bar can then be used as fine adjustment tool and is a good indication of
the position of the axis.
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Assemble Declination Axis
1. Do not have your telescope or counterweights connected to
the Dec. axis assembly for either assembly or disassembly
of the Dec. and RA axes.
2. Position the R.A. axis as shown in Diagram 7 with the
pocket "A" at the top, opposite the altitude adjuster knob.
Firmly tighten R.A. clutch knobs.
3. During shipment, the Dec. axis assembly lock knobs will be
fully screwed into the Dec. axis. For correct assembly, these
lock knobs should be unscrewed at least 7 full turns and no
more then 8.5 full turns. This is between 5/16" and 3/8" out
from the "shipped" tightened position.
Note: These lock knobs can be completely removed from
the Dec. axis assembly with about 9.5 full turns out.
4. Position the Dec. axis above the R.A. axis as shown in
Diagram 8, a light movement (wiggle) in the downward
direction (arrow "A") will help to correctly seat the principle
dovetail(s) and parallel guides.
5. When both Dec. and R.A. assemblies are fully seated, hand
tighten both Dec. lock knobs.
6. Thread the counterweight shaft into the Dec. axis.
7. Remove the hand knob and safety washer from the base of
the counterweight shaft. Add sufficient counterweights (10
or 18 lb. counterweights are purchased separately) to the
declination shaft to balance the telescope you intend to use.
Always use two hands to attach or move them on the shaft.
8. Reattach the hand knob and safety washer to the end of the
declination shaft. This will help to prevent injury if someone
accidentally loosens the counterweight knob.
NOTE: Firm tightening of the counterweight knob will not
damage the surface of the counterweight shaft. The pin that
tightens against the stainless counterweight shaft is
constructed of brass. Likewise the bronze sleeve that has
been press fit into the center of the counterweight will
prevent marring of the shaft as you move the counterweight
up and down.
Removing Declination Axis at the End of your Observing
Session
1. Unscrew the lock knobs 5.5 to 7 full turns (this is still 5/16"
to 3/8" out from the fully tightened position) and slide/tilt the
Dec. axis assembly in an upwards direction (arrow "B").
2. For transport/storage we recommend fully tightening the
lock knobs.
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Attach Mounting Plate (purchased separately)
Several mounting plates (also called cradle plates) are available for the 1200 mount. If you own more than one instrument,
you may need more than one plate. Follow the appropriate directions for the plate(s) that you have. The darkened holes
represent those used for the 1200 mount.
18" FLAT MOUNTING PLATE (FP1800)
This plate is 18" long and 7.5" at its widest point in the center. The
width of the plate tapers to 5.5" at each end. Four pairs of keyhole
slots that measure 3.2" between centers are provided. The two
inner pairs are 13.75" apart and the outer two pairs are 17" apart.
You can drill additional holes to suit your needs. This plate also fits
the 900 German Equatorial. Attach this plate with six 1/4-20 x 1"
flat head socket cap screws
15” RIBBED MOUNTING PLATE (1200RP15)
This plate is 14.75” long, 7.75” at its widest point 5” at each end
and 1” thick. The underside of the plate is carved into a ribbed
pattern to maximize the strength and minimize the weight - 3 lbs.
A pair of keyhole slots that measure 3.2” between centers are
provided at each end. The distance between the pairs is 13.75”.
Attach this plate with six 1/4-20 x 3/4“ socket head cap screws
Note that the plate is asymmetrical. In most cases, orient the
plate so that the long end points toward the sky. You can also
turn the plate in the other direction to balance your scope.
24" RIBBED MOUNTING PLATE (1200RP)
For larger instruments, the ribbed structure of this plate
provides the maximum support. Our machinist begins
with thick aluminum plate and carves a strong rib
structure. The final result is 1.5" thick, 24" long and 7.6"
at its widest point. The width of the plate tapers to 5.5"
at each end. A pair of keyhole slots that measure 3.2"
between centers are provided at each end. The
distance between these pairs of holes is 23". Due to the
ribbed structure, you may not be able to drill additional
holes for non-Astro-Physics mounting rings. The plate
weighs an amazing 9.5 lbs. for its size. This is a view of
the rib structure on the underside of the 24" plate.
Attach this plate with six 1/4-20 x1" socket head cap screws.
8.5” DOVETAIL FOR LOSMANDY D SERIES PLATE (DOVELM2)
This Astro-Physics plate attaches to the 400, 600E, 900 and 1200 mounts. If you already
own one of the Losmandy DAP series (fits Astro-Physics refractors), DC series (for
Celestron 8", 11" or 14" SCTs) or DM series (for Meade 8", 10" and 12" SCTs) plates, this
is the mounting plate for you.
Note that the bolt-hole pattern is offset from the center. This allows you to position the
plate either forward or backward depending on the balance point of your telescope. Attach
this plate with four 1/4-20 x 3/4" socket head cap screws and two 1/4-20x5/8" flat head
socket cap screws.
16" DOVETAIL FOR 1200 MOUNTS AND LOSMANDY D SERIES PLATES (DOVELM16)
This Astro-Physics plate attaches to the 1200 mount. If you
already own one of the 17.25” or longer Losmandy DAP
series (fits 6” and larger Astro-Physics refractors), DC series
(for Celestron 11" or 14" SCTs) or DM series (for Meade 10",
12" and 14" SCTs) plates, this is the mounting plate for you.
Note that the bolt-hole pattern is offset from the center. This
allows you to position the plate either forward or backward
depending on the balance point of your telescope. Attach
this plate with seven 1/4-20 x 1" socket head cap screws.
16
Understanding the R.A. and Dec. Clutch Knobs
We suggest that you read this before assembling the remainder of your system.
1. What do they do?
The four R.A. and four Dec. clutch knobs depicted in Diagram 2 have the function of connecting the R.A. and Dec.
axes to their respective drive worm wheel gears. Their function is progressive, from no tension (axes free to move
- as required during correct balancing of the telescope) to a completely "locked up" state.
2. How can you find out what they really do?
As shipped, all 1200 mounts have all four R.A. and Dec. clutch knobs firmly hand tightened. This will give you a
good idea of the maximum tightness (clutch action) that can be achieved by hand effort alone. At this point, you
must bear in mind that for optimum performance all four clutch knobs on each axis (R.A. or Dec.) should be
tightened evenly with the same tension i.e. all four half tight, all four fully tight, etc.
In order to feel the effect of the clutch knobs, you may wish to partially assemble your mount. Fit together the R.A.
and Dec. assemblies plus mounting plate and counterweight shaft. Do not put scope and counterweights on at
this stage. With the above assembly (with the clutch knobs firmly hand tightened - "as shipped"), you can feel the
amount of force needed to move each axis by hand. Grab each end of the telescope mounting plate and move it
with a backward and forward movement of the Dec. axis. You will feel considerable resistance to this motion.
Perform the same operation on the R.A. axis by moving the counterweight shaft backward and forward. With a
well-balanced telescope, the above tightness of the clutch knobs will be sufficient for all normal conditions of use.
Now, if you proceed to mount up and balance your telescope, you can "feel" what this resistance in R.A. and Dec.
(movement backwards and forwards) is like when you make these motions from the eyepiece end of your
telescope as you would during normal use when slewing (pushing) by hand to acquire an astronomical object
within the field of view of your finder or scope.
3. How tight can the clutch be and can you do any damage by pushing against them?
The maximum tightness of this clutch system is 1/3 turn (with a 5/32 allen key) further in than the tension you can
achieve with the knobs by hand. You will see that each clutch knob has a 5/32 hex socket for tightening with an
allen key. With this extra 1/3 turn on each clutch knob, the axis (axes) will be considered completely "locked up"
and you should not attempt to push your scope by hand against this "locked up" resistance, or undue stress will
be placed on the worm wheel/worm and bearings.
However, if you are undertaking a very long astrophoto exposure, it is advisable to increase the pressure on each
clutch knob (with the 5/32 key) by about 1/8 turn on Dec. and 1/8th turn on R.A. You may safely slew the scope by
hand with this tension, however you will notice considerably more effort is required to achieve movement. This is
the absolute maximum tension that can be used for hand slewing. As a general rule, if you have a big scope (7" or
8" refractor) with all the accessories, you will need more clutch tension than a 5" or 6" scope.
Resist the urge to overtighten the clutch knobs with the hex wrench. This will only cause them to deform and lock
into position. If you find that you are no longer able to adjust the tension and the knobs are locked firmly in place
so that the axis will not move, contact Astro-Physics for technical assistance.
Attach Counterweight Shaft and Counterweights
IMPORTANT:
• Always attach the counterweights before mounting the telescope to the cradle plate to prevent sudden
movement of an unbalanced tube assembly, which may cause damage or injury.
• Remember counterweights are heavy and will hurt if they fall on your foot.
1. Thread counterweight shaft onto the Dec. axis.
2. Remove the hand knob and washer from the end of the counterweight shaft. Add sufficient counterweights (10 or
18 lb. counterweights are available) to the shaft to balance the telescope you intend to use. Loosen the
counterweight knob and hold the counterweight with the knob pointing downward so that the brass pin will move
from the center opening allowing the counterweight to slide into position. Always use two hands to attach or move
them on the shaft.
3. Reattach the hand knob and washer to the end of the counterweight shaft. This will help to prevent injury if
someone accidentally loosens the counterweight knob.
A firm tightening of the counterweight knob will not damage the surface of the counterweight shaft. The pin that tightens
against the stainless counterweight shaft is constructed of brass. Likewise, the bronze sleeve that has been press fit into
the center of the counterweight will prevent marring of the shaft as you move the counterweights.
17
Attach Mounting Rings and Scope (purchased separately)
Flat and ribbed plates: Our flat and ribbed plates are constructed with keyhole slots at the location where your mounting
rings attach. This feature enables you to partially loosen the screws on your rings just enough to insert them into the larger
part of the keyhole, then slide the rings to the narrow part and tighten them with a hex key. We prefer this keyhole method
to the standard way of completely removing the screws and dropping them in the grass.
We suggest that you install the rings on the mounting plate, then open the rings, lift the scope in place, close the rings and
tightened the knobs. To balance the scope, you can loosen the knobs enough to slide the scope forward or backward as
needed.
Another approach is to attach the rings to the scope beforehand, then lift onto the mounting plate, However, the rings must
be spaced exactly the correct distance apart to match the holes in the plate. This maneuver may be particularly difficult to
accomplish with a large, heavy instrument.
Dovetail plates or sliding bars: Attach mounting rings to the male dovetail plate matching the appropriate threaded holes
on the bottom of the mounting ring. Again, you have the option of attaching this dovetail/ring assembly to the mount and
lifting your scope in or placing the scope in the rings, then lifting the entire assembly to the female mounting plate already
attached to the mount.
Balancing Your Telescope
For proper operation, the telescope must be adequately counterbalanced. Start by balancing the tube assembly.
1. Tighten the 4 R.A. axis clutch knobs.
2. Loosen the 4 Dec. axis clutch knobs (about 3/4 to 1 turn) so that the telescope moves freely about the declination
axis (be careful because if your telescope is significantly out of balance, it may swing rapidly in the out-of-balance
direction!)
3. Position the R.A. axis so that the counterweights are in their "lowest" position i.e. the declination axis assembly is
in the meridian (this is the usual way that German equatorials are depicted, as shown in diagram 2.)
4. Loosen the tube mounting rings and slide the tube up and down for balancing. This is best done with the tube in
the horizontal position. If you are using a dovetail mounting plate, loosen the hand knobs and slide the mating
plate to the desired position.
5. The scope is balanced when it stays put (does not move) with the clutches loose and movement back and forth
about the declination axis has the same feel in both directions.
6. Now, tighten the declination axis clutch knobs and position the telescope horizontal and the declination axis
horizontal. The center of the counterweights is now the same height as the middle of the tube.
7. Loosen the R.A. clutch knobs. Again, be careful, because if your scope is significantly out of balance, it may swing
rapidly in the out of balance direction).
8. Move the counterweight(s) up or down to achieve the correct balance in R.A. Movement back and forth about the
R.A. axis should have the same feel in both directions.
Try to anticipate any balance problems due to the extra weight of diagonals, heavy eyepieces, finders, solar filters, etc.
If the scope moves by itself, when the clutches are loose, then the scope is not counterbalanced adequately. If you are
doing astrophotography or imaging, a small amount of imbalance (more weight on the east side of the mount) is
permissible and indeed desirable.
Fine Polar Alignment
Now is the time to complete your final polar alignment. Please refer to the previous section for details.
18
SERVO MOTOR DRIVE
GTO Control Box – Model GTOCP3
The GTO control box contains all of the circuitry to drive the two servo motors and the logic required to navigate the sky. It
will be operational and track at the sidereal rate when connected to both motors of the mount and a power source. In order
to control the movement of the mount, you will need to connect at least one of these:
• GTO Keypad.
• PulseGuide by Sirius Imaging. The CD for this program is included with the mount. For the most updated version of the
software, check out the website www.pulseguide.com. Please refer to the section later in this manual for further
information regarding the capabilities of this program.
• Computer with astronomical software such as DigitalSky Voice or planetarium programs such as Software
Bisque’sTheSky™, Nova Astronomics’ The Earth-Centered Universe (ECU) version 3.1 or later, and Chris Marriot’s Sky
Map Pro 6 or any ASCOM compatible telescope software (all purchased separately).
The GTO Servo Control Box is mounted directly onto the polar axes of the 1200 mount. Please remember that this box
contains advanced electronics and must be treated with the same care given to other fine equipment. You can see that the
unit is built to be rugged, however it is not indestructible.
R.A. and Dec. Cable Connections
A “Y” cable with 10-pin connectors is included with your mount. Attach the connector from which the two cables emerge to
the GTO Control Panel. Attach the short part of the “Y” cable to the R.A. motor housing and the long part of the cable to the
Dec motor housing. Lock all connectors. Refer to the section below for further information about positioning the cables.
12V Connector
Place the DC power cord (included with your mount) into the phono plug outlet marked 12V on the GTO Control Panel and
lock in place. Plug the cigarette lighter plug end of the cord into your power source. The acceptable voltage range is 11.5 to
16.Suggested power sources include: portable rechargeable battery pack, auto or marine battery, or power supply (filtered
and regulated) for 110 volts with a minimum output of 5 amps at 12V DC.
There is no on-off switch. We recommend that you plug the power cable into the servo box after the keypad controller. To
turn the unit off, simply disconnect the power cable.
Considerations for observatory installations: We suggest that you disconnect your GTO Control Box from 110V and any
other device (CCD camera, computer, etc) when you are not using your mount so that if your observatory experiences a
power surge or lightening strike, your mount electronics will not be damaged. If you operate your mount remotely, you will
have to leave your power cable connected just as you do for the rest of your electronic equipment. You may want to
consider surge protectors or other protective measures to protect from voltage spikes. A disconnect relay to remove power
from both the 12-volt and ground wire is highly recommended in this situation.
19
POWER Indicator Light
This LED will remain illuminated when your power source has sufficient output to drive the motors. If the voltage falls below
10.5 volts, the power light will go out and the motors will stop. The keypad will not function properly.
For mounts shipped after 02-25-00: If the LED turns yellow, this means that your motors are overloaded, probably due to an
unbalanced load on your mount. Refer to the troubleshooting section of the manual for the solution. Earlier control boxes do
not have this feature.
KEYPAD Connector
Attach the 5-pin male connector of the keypad controller and lock in place (push in the knurled ring then turn).
RS-232 Connectors
These serial port connections are used to connect your mount to your PC computer. You must provide your own straight-
through (non-crossing) cables with a 9-pin (DB9) male connector to interface with the GTO panel. We have provided the
locking posts to secure the cable firmly. If your serial cable does not have a 9-pin connector, you can use a gender changer
or adapter to convert it. If your computer has USB ports, use a quality adapter to gain a serial port.
When you are controlling the position of the mount with a computer program such as DigitalSky Voice™ or Software
Bisque’s TheSky™, the microprocessor chip located in the servo drive box will send continual RA and Dec coordinate data
via the cable connections to your computer. When you use the software to give instructions to slew to a new object, the
commands (RA and Dec coordinates) are sent to the mount.
We provide two serial port connections on the mount so that you can use two software programs simultaneously. For
instance, you can use PulseGuide for advanced mount control, while using TheSky as a planetarium program. The
telescope control functions of TheSky are more limited so using both in a remote application is advantageous. Since the
mount will update the RA and Dec coordinates simultaneously, both programs are continually updated with the data from
the mount. You can watch the screen display of TheSky to see where your telescope is pointing as it slews. This is most
effective if you have a reasonably fast computer with plenty of RAM. If you try this with a 100MHz processor and only 32 MB
of RAM, the response time will be slow since both programs must be continuously updated with position data.
You must have two serial ports available on your computer to take advantage of this feature. If you use a laptop, you may
need to purchase a PCMCIA adapter to gain an additional serial port. Socket Communications offers adapters for many
computers. Check out their web site at www.socketcom.com.
FOCUS Connector
Attach the 3.5mm phono plug connector of your JMI Motofocus or other electric focuser (optional accessories) here. Refer
to the section regarding focus adjustment in the GTO Keypad Manual for instructions on using the keypad controller to
adjust focus. Alternatively, you can verbally control the focus using the Focus Mode of DigitalSky Voice software.
RETICLE Connector
If you wish to use the illuminator cable for our Polar Alignment Scope (PASILL3), a plug-in type guiding eyepiece with an
illuminated reticle (available from several manufacturers), insert the 3.5mm phono plug into this connector for power. Reticle
brightness can be adjusted with the keypad. Refer to the section pertaining to reticle illuminator adjustment in the GTO
Keypad Manual for further information.
AUTOGUIDER Connector
This connector interfaces with the RJ-11-6 modular jack of an autoguider cable, purchased separately or as part of a CCD
Imaging Camera or Autoguider. The autoguider will be functional and ready to go as soon as you plug it in. Please refer to
the appropriate manual from the manufacturer for operation of the autoguider.
We offer cables for all SBIG cameras. Please refer to our price list or call for further information.
+6V Connector
This 6-volt output accepts 3.5mm phono plugs. It is used primarily to power the Pentax 6x7 camera directly from the mount
with a cord sold for that purpose (our part # CORD01).
20
N and S Switch
Select northern (N) or southern (S) hemisphere as needed. When you slide the switch to the opposite position, the tracking
direction of the drive will reverse. The power cord must be removed and re-attached to make this work.
Removing the GTO Control Box From 1200 Mount
The GTO control box can be removed easily from the RA axis. It is secured by two 8-32 set
screws located at the base of the GTO Servo Control Box. Loosen the screws with one of
the hex keys from the set included with the mount. Lift the box up from the bottom and tilt so
that it frees from the dovetail connection.
Some people have a permanent observatory, yet prefer to store their electronics in their
home to keep them clean and free of cobwebs. If you do, you may wish to substitute the 8-
32 thumbscrews (included with your mount and shown in photo) for the setscrews. This will
allow you to remove and install your GTO control box without tools.
GTO KEYPAD OPERATION
Please refer to the manual for the GTO Keypad Controller for complete instructions.
PULSEGUIDE BY SIRIUS-IMAGING
See www.pulseguide.com for the latest information.
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