Gemini 3.75" Focuser/Rotator

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Gemini 3.75" Focuser/Rotator

# 1317200

€ 4,850.00 Price excl. German VAT tax (19%): € 4,075.63

Out of Stock  

  • Optec's heavy duty combination rotator and focuser for OTA's with limited backfocus incl. Gemini Controller Hub
  • Can be controlled through serial, USB, wired Ethernet and 802.11b WiFi networks
  • Can easily handle 10 kg (22 lbs) with Optec 4300 DM standard dovetail mounting system
  • Features two stepper motors with rotation and focus in one compact device. At only 2-1/4" thickness and 1/2-inch of travel, the Gemini will fit telescopes and long camera packages that previously could not be supported

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Optec Gemini Focusing Rotator

Gemini 3.75" Focuser/Rotator

Optec engineers have developed a completely new concept for combining telescope focus and camera rotation functions into a single robust, yet compact package. Rather than simply adding a rotator onto the end of a focuser drawtube, Gemini was designed from inception with a rotating drawtube providing superior strength and rigidity for heavy camera payloads.

Gemini Focusing Rotator at a glance:

  • Featuring four lead-screws and four linear bearings, Gemini can easily handle 10-kg. (22-lbs.) payload packages without flexure.
  • Full 360-degree rotation is a built-in function of the Gemini with a full 1/2" of linear travel.
  • Includes a remote temperature probe for automatic temperature compensation. Simply attach the temperature probe anywhere in the linear response zone of your OTA (usually the tube or truss assembly) and Gemini will automatically keep the camera package in sharp focus.
  • The Gemini Commander software provides a convenient wizard to help determine your telescope's TC or temperature coefficient.
Optec Gemini Focusing Rotator

Robust Compact Design:

To maintain a flat, rigid base for heavy camera packages, Gemini's shell consists of two parallel plates machined from MIC-6 tool plate providing flatness within 0.001" (25 microns). Seven precise stand-off spacers maintain the 2.2" separation of these plates.

The rotating drawtube is moved linearly with 1/2" of total travel using a premium timing belt driven by a high torque stepper motor. The entire package is accented with a carbon fiber wrap. Dual RJ45 connectors provide connection to the Gemini Control hub. The independent rotating drawtube is supported by a custom X-cage bearing system supported by large, 6mm chrome ball bearings.

Support for Multiple Telescopes

Featuring identical OPTEC-4300 mechanical interfaces front and back, the Gemini can be easily fitted to most any large telescope OTA. Recessed oval point setscrews provide three-point direct contact with the heavy wall OPTEC-4300 dovetail mount. Gemini's clear aperture of 3.75" is maintained through each adapter, passing even large light cones through to the camera image plane without vignetting.

Also camera-side suitable adapters of the OPTEC-4300 series and corresponding spacer rings are available. More information can be found on the original Optec Website.

Multiple Ways to Connect:

Optec Gemini Hand Controller

The Gemini Control hub acts as the central controller to link both focuser and rotator to any control PC. The hub includes communication ports for Serial and USB (using Optec's USB/Serial cable) and wired Ethernet Network protocols as standard. An optional WiFi board and antenna can be added and installed at any time. Focuser and Rotator ports are available at the top of the Gemini hub with 12VDC Power, Network, Hand Control, and Serial connection ports available at the bottom.

What's included

The Gemini package includes the updated Gemini Hand Controller which allows jiggle-free manual control while at the telescope. Now featuring a rotary encoder and integrated thumb knob, exact focus adjustments can be made without touching the telescope or focuser. Optecs precision external temperature probe, power supply, and ultra-flat Ethernet cables round out a complete integrated package.

802.11 WiFi Option:

Optec Gemini WiFi

Using the ASCOM Local Server model, Optec's Gemini Commander software allows multiple clients to connect simultaneously to the Gemini hub. Soon to be released embedded webservers in the wired Ethernet and WiFi connections enable Gemini to generate a control interface accessible through any web browser or smartphone. Free Android and iPhone applications search the local network and load the interactive webpages. Because these pages are generated by the hub itself, once you are connected, there is no further configuration required: just connect to Gemini and enjoy remote wireless focus control with the optional 802.11 WiFi add-on.

Gemini Commander Software

Gemini Commander Software

Gemini Commander creates an ASCOM Local Server or hub to allow multiple clients access for communication and control of the attached focusers. By using the local server model, Gemini offers an easily configurable user experience for all Windows ASCOM programs.

Visit the Gemini Software Download Page for the latest updates and ASCOM driver, Gemini Commander control software and additional resources.

Specifications for Gemini and Controller at a glance:

Focusing Rotator Physical Specifications:

  • Clear Aperture: 3.75" (95mm)
  • Back-Focus Usage: 2.2" to 2.7" (55.9 to 68.6mm)
  • Focuser Travel: 0.5" (12.7mm)
  • Focuser Resolution: 0.11 microns per step
  • Rotator Resolution: 600 steps per degree
  • Minimum Overall Thickness: 2.2" (55.9mm) [Full IN position]
  • Dimensions: 9.4" x 7.4" (239mm x 187mm)
  • Weight: 6 lb. 6 oz. (2.9 kg)

Gemini Hub Specifications

  • Length: 5.1" (130mm)
  • Width: 3.2" (81mm)
  • Height: 1.0" (27mm)
  • Weight: 10 oz.(285 g)
  • Mounting Holes: Four 4-40 x 1/8" depth (reverse side)
  • Case Material: 6061 aluminum, anodized black.

Gemini Hub Port Connections:

  • Focuser: RJ45 socket for standard Cat-5e/Cat-6 cable to Focuser port,
  • Rotator: RJ45 socket for standard Cat-5e/Cat-6 cable to Rotator port,
  • Power: 12VDC input, 2.5 x 5.5mm plug, center pin positive,
  • Network: Standard RJ45 Ethernet socket,
  • Hand Controller: RJ22 socket for standard telephone handset cord,
  • Serial: RJ12 socket for Optec USB/Serial cable (included),
  • Wireless: 802.11 WiFi option (coming soon).

If you have any further questions, please send us an email to kontakt (at)

Detailed information about the Optec motorfocuser program by Baader Planetarium can be found here.

Please note the additional details on the Tab "Downloads"


Additional Information

Manufacturer Optec
SKU (#) 1317200
EAN Code 4047825034380
Focuser Travel 0.5" (12.7mm)
Payload Capacity (kg) 22lb (10 kg)
Inner Diameter / Clear Aperture (mm) 3.75" (95mm)
Resolution Focuser: 0.11 microns per step, Rotator: 600 steps per degree
Required Backfocus 2.2" to 2.7" (55.9 to 68.6mm)
Software Gemini Commander Software
Width (mm) 9.4" (239mm)
Height (mm) 7.4" (187mm)
Thickness (mm) 2.2" (55.9mm) [Full IN position]
compatible telescopes Refractors, Schmidt-Cassegrain

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