iOptron GEM28 User manual

iOptron®GEM28 German Equatorial Mount
Instruction Manual
Product GEM28 and GEM28EC

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Read the included Quick Setup Guide (QSG) BEFORE taking the mount out of the case!
This product is a precision instrument and uses a magnetic gear meshing mechanism. Please read
the included QSG before assembling the mount. Please read the entire Instruction Manual before
operating the mount.
You must hold the mount firmly when disengaging or adjusting the gear switches. Otherwise
personal injury and/or equipment damage may occur. Any worm system damage due to improper
gear meshing/slippage will not be covered by iOptron’s limited warranty.
If you have any questions please contact us at [email protected]m
WARNING!
NEVER USE A TELESCOPE TO LOOK AT THE SUN WITHOUT A PROPER FILTER!
Looking at or near the Sun will cause instant and irreversible damage to your eye.
Children should always have adult supervision while observing.

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Table of Content
Table of Content.................................................................................................................................................3
1. GEM28 Overview ..........................................................................................................................................5
2. GEM28 Terms................................................................................................................................................6
2.1. Parts List..................................................................................................................................................6
2.2. Identification of Parts ..............................................................................................................................7
2.3. GEM28 Port.............................................................................................................................................8
2.4. Go2Nova®8409 Hand Controller ...........................................................................................................8
2.4.1. Key Description................................................................................................................................9
2.4.2. The LCD Screen...............................................................................................................................9
2.5. Check the Battery..................................................................................................................................10
2.6. Bench Testing the Mount ......................................................................................................................10
3. GEM28 Mount Assembly.............................................................................................................................11
3.1. GEM28 Mount Assembly......................................................................................................................11
4. Getting Started..............................................................................................................................................21
4.1. Setup the Mount and Polar Alignment..................................................................................................21
4.2. Manual Operation of the Mount............................................................................................................21
4.3. Initial Star Alignment............................................................................................................................21
4.4. Go to the Moon and Other Stars............................................................................................................21
4.5. Star Identifying Function.......................................................................................................................22
4.6. Power-Down Memorization..................................................................................................................22
4.7. Turn Off the Mount...............................................................................................................................22
4.8. Putting the Mount Back into the Package .............................................................................................22
5. Complete Functions of Go2Nova®8409 Hand Controller...........................................................................23
5.1. Slew to an Object...................................................................................................................................23
5.1.1. Solar System...................................................................................................................................23
5.1.2. Deep Sky Objects...........................................................................................................................23
5.1.3. Stars:...............................................................................................................................................23
5.1.4. Constellations.................................................................................................................................23
5.1.5. Comets............................................................................................................................................23
5.1.6. Asteroids.........................................................................................................................................23
5.1.7. User Objects ...................................................................................................................................23
5.1.8. Enter R.A. DEC..............................................................................................................................24
5.2. Sync to Target........................................................................................................................................24
5.3. Alignment..............................................................................................................................................24
5.3.1. Pole Star Position ...........................................................................................................................24
5.3.2. One Star Alignment........................................................................................................................24
5.3.3. Two Star Polar Align......................................................................................................................24
5.3.4. Three Star Align .............................................................................................................................25
5.3.5. Polar Iterate Align ..........................................................................................................................25
5.3.6. Solar System Align.........................................................................................................................25
5.3.7. Display Model Error.......................................................................................................................25
5.3.8. Clear Alignment Data.....................................................................................................................25
5.4. Settings ..................................................................................................................................................26
5.4.1. Set Time and Site............................................................................................................................26
5.4.2. Set Beep..........................................................................................................................................26
5.4.3. Set Display......................................................................................................................................26
5.4.4. Set Maximum Slew Rate................................................................................................................26

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5.4.5. Set Guiding Rate.............................................................................................................................26
5.4.6. Set Parking Position .......................................................................................................................27
5.4.7. Set Tracking Rate...........................................................................................................................27
5.4.8. Meridian Treatment........................................................................................................................27
5.4.9. Set Altitude Limit...........................................................................................................................27
5.4.10. Wi-Fi Option ................................................................................................................................27
5.4.11. GPS Status....................................................................................................................................27
5.4.12. Language ......................................................................................................................................28
5.4.13. Set RA Guiding (GEM28EC Only)..............................................................................................28
5.5. PEC Option............................................................................................................................................28
5.5.1. PEC Playback.................................................................................................................................28
5.5.2. Record PEC....................................................................................................................................28
5.5.3. PEC Data Integrity .........................................................................................................................28
5.6. Edit User Objects...................................................................................................................................29
5.6.1. Enter a New Comet ........................................................................................................................29
5.6.2. Enter Other Objects or Observation List........................................................................................29
5.7. Firmware Information ...........................................................................................................................30
5.8. Zero Position .........................................................................................................................................30
5.8.1. Goto Zero Position .........................................................................................................................30
5.8.2. Set Zero Position ............................................................................................................................30
6. Maintenance and Servicing ..........................................................................................................................31
6.1. Maintenance ..........................................................................................................................................31
6.2. iOptron Customer Service.....................................................................................................................31
6.3. Product End of Life Disposal Instructions ............................................................................................31
6.4. Battery Replacement and Disposal Instructions....................................................................................31
Appendix A. Technical Specifications.............................................................................................................32
* OTA size and length dependent, smaller than 6” in diameter recommended. ** Measured with encoder on
bench, 10 minutesAppendix B. Go2Nova®8409 HC MENU STRUCTURE .................................................32
Appendix B. Go2Nova®8409 HC MENU STRUCTURE ..............................................................................33
Appendix C. Gear Meshing Adjustment ..........................................................................................................36
Appendix D. Firmware Upgrade......................................................................................................................38
Appendix E. Computer Control an GEM28 Mount .........................................................................................39
Appendix F. Go2Nova®Star List.....................................................................................................................40
IOPTRON TWO YEAR TELESCOPE, MOUNT, AND CONTROLLER WARRANTY.............................49
Ver. 1.1 2021.2
iOptron reserves the rights to revise this instruction without notice. Actual color/contents/design/function may differ from those described in this
instruction.

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1. GEM28 Overview
The iOptron®GEM28 and GEM28EC mount is the next-generation compact German equatorial
mounts. Like their predecessors the GEM28 is designed with portability in mind, weighing in at only 10 lbs it
can support up to a 28lb payload an incredible 2.8 mount weight to payload ratio. We achieved this using
design methods developed to reduce mount mass in our CEM family of mounts. The German EQ versions
were created to satisfy consumer that prefer a more traditional mount and to function at higher latitudes.
Building on the legacy of earlier GEM models, such as iEQ30/45 mounts, we have added features
for convenience and functionality. A positive lock gear engagement system (easy to use even when wearing
gloves), Built-in Wi-Fi enabling unparallel connectivity and recordable permanent periodic error correction
(PPEC) to repeat optimal PEC training sessions (real time PEC on the GEM28EC). Regarding functionality
the GEM28 and GEM28EC delivers precise pointing and accurate tracking (PE <0.3 arcsec rms on the EC
model). The 212,000 object library ensures you’ll never run out of targets to see or image. The GEM28 and
GEM28EC set the new standard for compact equatorial mounts.
The mount has an integrated electronic polar finder scope known as the iPolar, or an AccuAlignTM
optical polar scope. The iPolar ensures the accurate alignment of a telescope, even when the pole star is
obscured.
The iOptron GEM28 mount uses the new Go2Nova® 8409 hand controller to navigate the night sky.
This incredible technology helps observers find celestial objects with the aid of the mount's 212,000+ object
database! For those looking for a telescope that has the capability of tracking and finding beautiful night sky
objects, this mount is a must have tool.
Features:
German equatorial design, latitude range of 10° ~ 70°
Ideal for both visual observation and astrophotography
Low periodic error (< ± 10 arcsec for GEM28 and <0.3 arcsec for GEM28EC)
Payload of 12.7 kg (28 lbs) with the mount-only weight of 4.5 kg (10 lbs)
Spring loaded gear system
Large easy to use quick-lock gear clutches
Stepper motor with low power consumption
Integrated iOptron iPolarTM electronic polar scope or AccuAlignTM dark field polar scope
Polar alignment routine for those who can’t see the Pole Star
Go2Nova®8409 controller with Advanced GOTONOVA®GOTO Technology
Integrated ST-4 autoguiding port
Built-in Wi-Fi
USB port for firmware upgrade and computer control
Standard 1.5 inch heavy-duty stainless steel tripod (5kg), optional LiteRocTM tripod (7.5kg)
Die-cast metal tripod spreader with accessory tray
Optional external 32-channel Global Positioning System (GPS)
Optional hard carrying case (standard for EC model)
Optional iGuiderTM autoguiding system #3360

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2. GEM28 Terms
2.1. Parts List1
SHIPPING CONTENTS
Your new GEM28 mount comes in two shipping boxes. One box contains a GEM28/GEM28EC
mount, hand controller, one 10.4 lbs (4.7kg) counterweight, counterweight shaft, tripod spreader and
accessories. The other box contains a tripod.
iOptron®GEM28 mount head with iPolar (#G28xAx), or
iOptron®GEM28 mount head with AccuAlignTM optical polar scope (#G28xBx), or
iOptron®GEM28EC mount with iPolar (#G284Ax, with red gear switch)
Go2Nova®8409 Hand Controller with USB port
One 10lbs (4.5 kg) counterweight
Stainless steel counterweight shaft
Internal iPolarTM electronic polar scope or AccuAlignTM optical polar scope
AC adapter (100V-240V)
2X coiled control Cable (6P6C RJ11 to RJ11, straight wired)
USB cable for mount
USB cable for iPolar or LED and cable for optical polar scope
Aluminum carrying case (for GEM28EC and mount w/case)
1.5” tripod or LiteRocTM tripod
Quick Start Guide
OPTIONAL PARTS
External GPS module (#8438)
iGuider 1 mini autoguiding system (#3360)
Hard case (#C268)
ONLINE RESOURCES (click on the “Support” menu at www.iOptron.com)
Quick Start Guide
Instructional manual
Tips for set up
Hand controller and mount firmware upgrades (check online for latest version)
iOptron ASCOM driver
Reviews and feedback from other customers
Accessories
1US market only. Actual contents, design and function may vary.

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2.2. Identification of Parts
Az. adj. knob
Polar scope
Tripod
DEC gear switch
Polar axis cover
DEC Unit
CW safety screw
Counterweight
CW bar
Dovetail saddle
Azi. locking screw
Alt. adj. knob
RA Unit
Alignment Peg
Accessory Tray
Tray Locking Knob
Figure 1.GEM28 mount assembly

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2.3. GEM28 Port
Figure 2. Ports on a GEM28 mount
On RA Unit:
I/O Switch: Power switch
LED: Power indicator
DC 12V IN: DC power socket to power the mount (2.1mmX5.5mm, center positive)
HBX (Hand Box): For connecting to an 8409 Hand Controller
GUIDE: ST-4 compatible autoguiding port. The wiring is shown in Figure 3
Figure 3. ST-4 Compatible Guiding Port Wiring
DC 12 OUT: DC power socket for optical polar scope LED
DEC: For connecting to DEC drive unit
On DEC unit:
DEC: Connect the DEC drive unit to RA unit via RJ11 cable
iPORT: Auxiliary port for connecting to other iOptron accessories, such as a GPS receiver or an
electronic focuser. DO NOT plug ST-4 guiding camera cable into this port, It will damage the
guide camera electronics.
2.4. Go2Nova®8409 Hand Controller
The Go2Nova®8409 hand controller (HC) shown in Figure 4 is the standard controller used on the
GEM28 mount. It has a large LCD screen, function, direction, and number keys on the front; and an HBX (6-
pin) and a USB port at the bottom.
DEC Unit
RA Unit (Top)
RA Unit

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Figure 4. Go2Nova®8409 hand controller
2.4.1. Key Description
MENU Key: Press “MENU” to enter the Main Menu.
BACK Key: Move back to the previous screen, or end/cancel current operation, such as slewing.
ENTER Key: Confirm an input, go to the next menu, select a choice, or slew the telescope to a
selected object.
Arrow (▲▼◄►) Keys: The arrow keys are used to control the movement of DEC and R.A. axes.
Press and hold ▲(DEC+),▼(DEC-) buttons to move a telescope along the DEC direction,
◄(R.A.+), ►(R.A.-) to move a telescope along the R.A. direction. They are also used to browse
the menu or move the cursor while in the menu. Press and holding an arrow key for a fast
scrolling.
Number Keys: Input numerical values. Also used to adjust speeds (1: 1X; 2: 2X; 3: 8X; 4: 16X; 5:
64X; 6: 128X; 7: 256X; 8: 512X; 9: MAX)
Help (?) Key: Identify and display bright stars or objects that the telescope is pointing to.
0 Key: Stop the mount during GOTO. Also toggling between starting and stopping tracking.
HBX (Handbox) port: connect the HC to the GEM28 mount using a 6P6C RJ11 cable.
USB port: connect the HC to a computer for firmware upgrade and computer control.
2.4.2. The LCD Screen
The 8409 HC has a large 4-line, 21-character per line LCD screen. The user interface is simple and
easy to learn. When the mount first turned on, an initial information screen will be displayed as shown in
Figure 5, after company logo displayed. It displays the Zero Position, current date and time.
Figure 5. 8409 Initial Information Screen
HBX
Port
USB
Port
RA+
RA-
DEC-
DEC+

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The LCD screen will switch to the information screen, as indicated in Figure 6, with pressing any
button.
Figure 6. 8409 HC LCD Information Screen
1. Target Name/Mount Position: displays the name of the target that telescope is currently pointed to or
the current mount position.
An object name, such as “Mercury” or “Andromeda Galaxy”: Name of the Star or celestial object
that the mount is currently slewing to, GOTO or tracking;
User Position: The mount is point to a user defined position, which could be a real sky object or
just simply due to press an arrow key.
2. Magnitude: the magnitude of the current celestial object
3. Right Ascension: Right Ascension of the telescope, or R.A.
4. Declination: Declination of the telescope, or DEC.
5. Azimuth: Azimuth of the telescope (north is 0º, east 90º, south 180º, and west 270º).
6. Altitude: Altitude of the telescope (degrees vertical from the local horizon - zenith is 90º).
7. Mount Status: Display current operation status of the mount.
Stop: mount is not moving;
Slew: mount is moving with an arrow key is pressed;
GoTo: mount is slewing to a celestial object using “Select and Slew”;
8. Slew speed: It has 9 speeds: 1X, 2X, 8X, 16X, 64X, 128X, 256X, 512X, MAX(1440X, or 6°/sec).
9. Current Time: display local time in a format of HH:MM:SS.
2.5. Check the Battery
The hand controller has a real time clock (RTC) which should display the correct time every time the
mount is turned on. If the time is incorrect, please check the battery inside the hand controller and
replace it if needed. The battery is a 3V lithium button battery.
2.6. Bench Testing the Mount
The counterweight shaft is designed to counter balance the mount’s own weight. It is recommended
that the CW shaft is installed when testing the mount’s function.
NEVER operate the mount with only the counterweight or OTA on it. It may cause gear slippery and
cause the worm and gear damage.
Target Name
Right Ascension
Mount Status
Azimuth
Slew Speed
Current Time
Altitude
Declination
N/S Hemisphere
Magnitude

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3. GEM28 Mount Assembly
3.1. GEM28 Mount Assembly
NOTE: The GEM28 mount is a precision astronomical instrument. It is highly recommended that you
read the entire manual and become familiar with the nomenclature and function of all components
before starting the assembly.
WARNING: DO NOT rock the counterweight shaft rigorously. This may damage the
worm/drive gear system and such damage will not be covered by warranty.
Step 1. Remove mount head from package
The RA axle is locked by an Allen wrench (blue circle). Make sure it is inserted all the way in. Check
the R.A. and DEC Gear Switches and make sure they are at the unlock position before removing it from the
box.
Figure 7. GEM28 mount in a case
Step 2. Set up tripod
The mount has a 102mm base. Thread the Alignment Peg onto the tripod head, on top of a tripod
leg or between two legs depending on the latitude. Insert the Accessory Tray through the center rod and
secure the setup by tightening Locking Knob from underneath.
Figure 8. GEM28 tripod top

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Step 3. Attach mount head
Before put the mount onto the tripod, make sure the RA gear switch is at lock position to
prevent mount head free swing by accident! Retract the 2x Azimuth (Azi) Adjustment Screws from both
sides to leave ample space for the alignment peg to be fitted in between the 2x Azi Adjustment Screws.
Remove the 2x Azi Locking Screws from the mount base and insert them into the opening next. Secure the
mount head by tightening the Azi Locking Screws into the M6 holes on the tripod.
Figure 9. Attach the mount
Level the mount by adjusting the tripod legs. Use the build-in Bubble Level Indicator or an external
leveler for this purpose.
Step 4. Adjust latitude
Pull the Allen wrench out from the RA axle. Rotate the mount head 180º around the R.A. axis to
move the dovetail face upside. There are four RA axle locking positions for the GEM28 mount: Zero
Position, East and West position, and storage position.
Figure 10. Rotating GEM28 mount head upward
Loosen the Latitude Locking Lever. Turn Latitude Adj. Knob to adjust the latitude until the arrow
points to the current latitude on the Latitude Scale. You may use the Allen wrench for easy adjustment.
Tighten the Latitude Locking Lever.
Azi. Adj. Screw
Azi. Locking Screw

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Figure 11. Adjust latitude
You may lift the Latitude Locking Lever handle by push the Push Button on this ratchet lever to
disengage gear teeth and rotate freely for quick adjustment.
There are four RA axle locking positions for the GEM28 mount: Zero Position, East and West
position, and storage position.
Figure 12. Allen wrench to lock the RA axle and storage
The Allen wrench can be stored on the bottom of the mount, as show in Figure 12.
Step 5. Install counterweight (CW) shaft
Unscrew the CW shaft from the top of the mount as shown in Error! Reference source not
found.(a) and thread it into the opening of the DEC axis as shown in Error! Reference source not
found.(b).
Figure 13. Install counterweight shaft
Lat. Adj. Knob
Latitude Scale
Wrench
Latitude Locking Lever
Push Button

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Step 6. Install counterweight
Before putting on CW, make sure the mount is at its zero position, i.e., CW shaft points to the
ground. Insert Allen wrench to lock the RA axle and disengage the R.A. Gear Switch to set the R.A. axis
free before loading the CW.Remove the CW Safety Cap at the end of CW Shaft. Glide the CW over the
shaft with the larger opening facing down. Tighten the CW Locking Screw to hold the CW in place. Place
the Safety Cap back onto the shaft. Move the CW to the bottom of the shaft and tighten the CW locking
Screw.
GEM28 comes with a 10.4 lbs (4.7 kg) CW, which should be sufficient for an 6” scope with total
payloads up to about 12 lbs. Use extra CW or CW Extension Bar to balance higher payloads.
Figure 14. Install counterweight
Step 7. Install telescope
GEM28 has a 3.5” Vixen dovetail saddle, with a Center Adjusting Block. This can be used to
accommodate dovetail bars with different width and keep the OTA centered. Release the locking screws
(blue circled) on the Center Adjusting Bar first. Adjust the setting screws (red circled) to move the center
block in or out. Then tighten the locking screws. Tighten the set screws at last.
Figure 15. GEM28 Vixen dovetail saddle with Center Adjusting Block
Saddle Locking Knob
Center Adjusting Block

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To mount a telescope on to the mount, release the dovetail Saddle Locking Knob and slide the
telescope dovetail plate into the saddle. Tighten the Saddle Locking Knob.
There are two threaded holes on the side of the dovetail saddle for mounting an iOptron mini
autoguiding system, iGuider.
Figure 16. iGuider mini-autoguiding system
Step 8. Balance payload
After attaching the scope and accessories, the mount head assembly must be balanced in both DEC
and RA axes to ensure minimum stresses on the mount driving mechanism.
CAUTION: The telescope may swing freely when the R.A. or DEC Gear Switch is disengaged.
Always hold on to the mount and/or telescope assembly before releasing the Gear Switches to
prevent it from sudden swinging, which can cause personal injuries and/or equipment damages.
Set the mount at Zero Position. Disengage both RA and DEC gear switches and move the mount to
horizontal position to check balance. Return to Zero Position for balance adjustment. Balance the DEC axis
by moving the scope with accessories back and forth in the mount saddle or within the scope mounting
rings. Balance the assembly in R.A. axis by moving CW along its shaft. Repeat the process until both DEC
and RA axes are balanced.
Figure 17. Balance a telescope
CAUTION: The balancing process MUST be done with Gear Switch at the total disengaged position!
Otherwise it might damage the worm system.
Return the mount to Zero Position after balancing and engage gear switches.
Step 9. Connect cables
Use the short RJ11 cable to connect the DEC control unit to the DEC port of the RA control unit.

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Figure 18. Connect DEC cable
Connect the Go2Nova®8409 Hand Controller to the HBX port on the RA unit. Plug in a 12V DC power
supply to the DC12V IN socket next to the HBX port (NOT the DC12V OUT on the other side).
Figure 19. Ports for cables
Plug optional GPS module into the iPORT with a coiled cable. When powering on, GPS ON sign
should be displayed at the upper right corner of the hand controller. You may disconnect the GPS module
after it picks up satellites signals and displays GPS OK. (It takes a few minutes in normal conditions).
STEP 10. Set hand controller
If a GEM28 is equipped with a GPS receiver, it will receive the time, longitude and latitude
information from satellites after the link is established. However, there are still some parameters need to be
entered to reflect your location, such as time zone info (UTC offset) and daylight saving time (DST). The
information will be stored inside the hand controller memory along with longitude and latitude coordinates
until they need to be changed.
A clear sky and open space outside is needed for the GPS to establish its link with the satellites. The
GPS is installed on top of the R.A. motor control board. Do not leave the hand controller on GPS Status
submenu waiting for GPS ON tuning into GPS OK.
To set up the controller, turn the mount power ON. Press MENU=> “Settings”:
Press ENTER and select “Set Time and Site”
Select and Slew
Sync. to Target
Alignment
Settings

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Press ENTER. A time and site information screen will be displayed:
Set Local Time
The time will be updated automatically when the GPS receiver has established its link with the GPS
satellites. In the event that the GPS module is unable to establish a link to the satellites, local time can be
entered manually. Use the ◄or ► key to move the cursor _ and use the number keys to change the
numbers. Use the ▲or ▼button to toggle between “Y” and “N” for Daylight Saving Time, or “+” and “-“ for
UTC (Coordinated Universal Time) setting. Hold the arrow key to fast forward or rewind the cursor.
In order to make the hand controller reflect your correct local time, time zone information has to
be entered. Press the ◄or ► key, move the cursor to the third line “UTC -300 Minute(s)” to set the time
zone information (add or subtract 60 minutes per time zone). For example:
Boston is “UTC -300 minutes”
Los Angeles is “UTC -480 minutes”
Rome is “UTC +60 minutes”
Beijing is “UTC +480 minutes”
Sydney is “UTC +600 minutes”
All the time zones in North America are “UTC –”, as shown in the following table, so ensure the
display shows “UTC -” instead of “UTC +” if in North or South America.
Time Zone
Hawaii
Alaska
Pacific
Mountain
Central
Eastern
Hour behind UT
-10
-9
-8
-7
-6
-5
Enter UTC
-600
-540
-480
-420
-360
-300
To adjust minutes, move the cursor to each digit and use the number keys to input the number
directly. Use ▲ or ▼ key to toggle between “+” and “-”. When the time information entered is correct, press
ENTER and go back to the previous screen. Note that fractional time zones can be entered.
Do not manually add or subtract an hour from displayed time to reflect Daylight Saving Time (DST).
Instead please select “Y” for DST when daylight saving time begins.
For other parts of the world you can find your “time zone” information from internet.
Set Observation Site Coordinate
The third and fourth lines display the longitude and latitude coordinates, respectively. The longitude
and latitude coordinates will be automatically updated when the GPS picks up satellite signals. “W/E”
means western/eastern hemisphere; “N/S” means northern/southern hemisphere; “d” means degree; “m”
means minute; and “s” means second.
If, for any reason, your GPS can’t pick up a signal, you can manually enter the GPS coordinates.
Press ◄or ► key to move the cursor and using ▲ or ▼ key to toggle between “W” and “E”, “N” and “S”,
using number key to change the numbers. It is always a good idea to do your home work to get the GPS
coordinates before traveling to a new observation site.
2020-10-01 12:01:36
UTC -300 Minute(s)
W071d08m50s DST: N
N42d30m32s Northern
Set Time and Site
Set Beep
Set Display
Set Guiding Rate
Daylight Saving Time

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The site coordinates information can be found from your smart phone, GPS receiver or via the
internet. Site information in decimal format can be converted into d:m:s format by multiplying the decimal
numbers by 60. For example, N47.53 can be changed to N47º31'48”: 47.53º = 47º +0.53º,
0.53º=0.53x60'=31.8', 0.8'=0.8x60"=48". Therefore, 47.53º=47º31'48" or 47d31m48s.
Select N/S Hemisphere
If the polar axis is aligned to the North Celestial Pole, then set the mount to Northern Hemisphere. If
the polar axis is pointing to the South Celestial Pole, set the mount to Southern Hemisphere. Press the ◄or
►key to move the cursor and use the ▲ or ▼ key to toggle between “Northern Hemisphere” and “Southern
Hemisphere”.
As an example, select Northern Hemisphere if you are located in US and press ENTER to go back
to the main menu.
The time and site information will be stored inside the hand controller’s memory chip. If you are not
traveling to another observation site, they do not need to be changed.
Check the Hand Controller Battery
The hand controller has a real time clock which should display the correct time every time the mount is
turned on. If the time is off too much, please check the battery inside the hand controller and replace it if
required. The battery is a 3V lithium button battery.
STEP 11. Perform polar alignment
A GEM28 mount may be equipped with an iPolarTM electronic polar scope or an AccuAlignTM optical
polar scope.
iPolar Polar Alignment
For a GEM28 with an iPolar, refer to iPolar Operation Manual from iOptron’s website to perform the
polar alignment, or steps briefly outlined below:
Download and install iPolar Software (first time use);
Connect a mini USB cable between the iPolar and a computer USB port;
Figure 20. USB port on an iPolar electronic polar scope
Click Connect and start polar alignment by following on screen instructions.
Quick Polar Alignment
If the mount equipped with an AccuAlignTM optical polar scope, you can use the Quick Polar
Alignment procedure to perform the polar alignment. One of the GEM28’s unique features is that the polar
scope can be used at anytime as it is not blocked by DEC axle as is the case in a German Equatorial
Mount. This makes it possible to adjust the polar alignment while the mount is tracking.

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As indicated in Figure 21, the Polar Scope reticle has been divided into 12 hours along the angular
direction with 10-minute tics. There are 6 concentric circles in 2 groups of 3 marked from 36’ to 44’ and 60’
to 70’, respectively. The 36’ to 44’ concentric circles are used for polar alignment in the Northern
Hemisphere using Polaris, while the 60’ to 70’ circles are used for polar alignment in Southern Hemisphere
using Sigma Octantis.
Figure 21. Polar Scope
Figure 22. Connect polar scope LED
To perform the polar alignment:
(1) Level the GEM28 mount and set it to the Zero Position. Make sure the telescope optical axis is
parallel to the polar axis (R.A. axis) of the mount. If using a finder scope, adjust it to be parallel to
the telescope optical axis.
(2) Remove both the polar axis cover. Thread the polar scope LED to the Polar Scope. Connect one
end of the polar scope power cable to the illumination LED and the other end to the DC12V output
located on RA Unit (Figure 22).
(3) Turn the mount power on.
(4) Adjust the polar scope dial to rotate one of the major ticks at the top.
(5) Use the Hand Controller (MENU => “Alignment” => “Position of Polaris/SigmaOct”) to display
the current position of Polaris on the LCD screen, as indicated in the left side of the figure below.
For example, June 22, 2014, 20:19:42 in Boston, US (long. W71°08’50” and lat. N42°30’32”, UTC -
300 min,) the Polaris Position is 0h45.8m and 40.4m.
(a) (b)
Figure 23. Polaris position shown on HC (a) and where to put on polar scope reticle (b)
(6) Look through the polar scope to find the Polaris. Use the Azimuth and Latitude Adj. Knobs to adjust
the mount in both directions and put the Polaris in the location on the Polar Scope Dial (same as
indicated on the HC LCD), as shown in In Error! Reference source not found. (b).

20
NOTE: If you are located in the Southern Hemisphere, Sigma Octantis will be chosen for Polar
Alignment.
BrightStar Polar Alignment
If you mount does not have an iPolar installed, or the pole star is not in sight, you may use two bright
stars with Polar Iterate Align to do the polar alignment.
(1) Level the mount and set it to the Zero Position. Align the telescope to the R.A. axis of the mount.
If a finder scope is used, adjust it to be parallel to the telescope optical axis.
(2) Use the HC (MENU => “Alignment” => “Polar Iterate Align”) to display the azimuth and altitude
position of several bright stars near the meridian. Select one that is visible at a high altitude as
Alignment Star A. Follow the HC instruction to move Alignment Star A to the center of the
eyepiece using a combination of the Latitude Adjustment Knob and the “◄” or “►” buttons.
Press ENTER to confirm when the star is centered. Next, select a bright star that is close to the
horizon as Alignment Star B. Center it using the Azimuth Adjustment Knob and the “◄” or “►”
button (the “▲” and “▼” buttons are not used here). Press ENTER to confirm the settings.
(3) The telescope will now slew back to Alignment Star A. Repeat the steps above. The iteration can
be stopped when it is determined that the alignment error has been minimized. Press the BACK
button to exit the alignment procedure.
NOTE: It is highly recommended to use an eyepiece with an illuminated crosshair for accurate centering.
NOTE: The movement of the alignment star in your eyepiece may not be perpendicular depending on its
location in the sky.
STEP 11. Return Mount to Zero Position
After polar alignment and balancing OTA, return the mount to Zero Position. The Zero Position is the
position with the CW shaft pointing toward the ground, OTA at the highest position with its axis parallel to
the polar axis and the OTA pointing to the Celestial Pole.
To set the mount to Zero Position, press MENU=>”Zero Position”=>”Set Zero Position”. Release
the Gear Switch to manually return the mount to Zero Position, or use the hand controller to slew the mount
to Zero Position. Press ENTER to confirm the zero position.
Set the Zero Position or check the Zero Position by using MENU=>”Zero Position”=>”Goto Zero
Position” before each session.