Astrodon - MonsterMOAG 3'' Standalone Off-Axis Guider - 3 Guide Port

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The Astrodon MOAG means Manual Off-Axis Guider.  It allows the user to guide their telescope to obtain sharp, round stars by guiding in front of your filters using unfiltered light in the same optical beam as the imaging camera.

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Product Description

Astrodon MonsterMOAG 3" Standalone Off-Axis Guider 3 Guide Port

MOAG means Manual Off-Axis Guider.  It allows the user to guide their telescope to obtain sharp, round stars by guiding in front of your filters using unfiltered light in the same optical beam as the imaging camera.  This is particularly important for practical use of narrowband filters. It also eliminates potential differential flexure if you guide with a separate guide scope. With modern, automated data acquisition programs, framing your imaging target and placing a guide star in the guide camera is simple and no longer an issue, particularly if you have a remotely-controlled camera rotator.

Astrodon's MonsterMOAG™ (MMOAG) is specifically designed to accommodate the larger CCD imaging detectors (36 x 36 mm), such as the Kodak KAF16803E and KAF9000E.  Furthermore, at 1.25" thick, it has one of the thinnest backfocus for an OAG available, making  MonsterMOAG™ an ideal choice for systems with minimal backfocus, such as the Takahashi FSQ106N refractor.  However, it is strong enough to handle heavy loads from larger cameras and filter wheels.

When installed, the MonsterMOAG becomes a fixed part of your optical train along with your camera and filter wheel.  When the user rotates tje camera at the back of the telescope, these three components will rotate together.  This means that the guide camera location will be fixed relative to the imaging camera.  The user can define this once as your Field-Of-View-Indicator (FOVI) in programs like Software Bisque's TheSkyX.   Then it can frame your target while ensuring that the guide camera has a star to guide on.

The new MMOAG-1,2,3,4  introduces the capability of attaching up to 4 guide ports to the MonsterMOAG. This was accomplished by making the body square and adding a hole on each side for insertion of the pick-off prism from the guide port assembly.  Thus, one possibility could include one guide camera and one 1.25" eyepiece, for example.  Any unused guide port will be shipped with a removable black metal plate.  Extra guide port assemblies can be ordered at a later date. The thickness (backfocus) and adapters are the same as before.  

Please see Astrodon's Optical Layout and Scope-Side Connections pages to help configure your MMOAG with the correct adapters for your system.

  • For largest CCDs (KAF16803, KAF9000)

  • Small backfocus 1.25" of the body

  • Total backfocus with both provided adapters is 1.45"

  • Solid body to hold large camera, filter wheel, filters

  • Large central opening of 2.55"

  • Guide in front of your filters

  • More and brighter guide stars with unfiltered light

  • Guide in the main optical beam

  • Avoid differential flexure of guide scope

  • Fixed guider position for automated data acquisition

  • Helical focuser for precision focusing of guide camera

  • Shorter 1.25" manual holder for guide camera also provided if the helical focuser is too tall to reach focus

  • Male 2.7"-24 scope-side adapter (0.1" thick) included

  • Female 2.7"-24 / Male 3"-24 camera-side adapter (0.1" thick) included

  • Adapters have dovetail connections to prevent tilt

  • Adapters can be rotated and locked to align with telescope and camera

  • Wide variety of adapters and different backfocus

  • Additional guide port assemblies come with prism, prism spacers, oval holder, helical focuser and 1.25" manual holder


Astrodon has simply made a male 2.7" adapter to bypass having to make separate adapters for all different connection possibilities with reducers, field correctors, focusers, rotators, etc. A customer adapter will be needed in most cases which can be found at The user can specify the threads on both sides of the part  and will render a result for the user immediately.

For observers that have Takahashi FSQ and TOA, the CAA-APF (0.4") adapter can be added along with a Spacer27 to convert the back of the 100mm camera-angle-rotator from 92mm to 2.7"-24 female threads. The MonsterMOAG then screws into this. The Spacer27, a 0.2" thick 2.7" washer/spacer is need also.

For observers that own a Meade or Celestron Schmidt-Cassegrain Telescope (SCT) with 3.25" visual backs, a 3.25" female to 2.7" female adapter from Astro-Physics is available (Celestron - ADASCTLC27; Meade - ADASTLM27. It will screw onto the visual back of the SCT and will accept 2.7" male threads from MonsterMOAG. This will allow off-axis guiding in the main beam without differential flexure effects with guide scopes or mirror movement during tracking.


Name Astrodon - MonsterMOAG 3'' Standalone Off-Axis Guider - 3 Guide Port
Manufacturer Astrodon


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