Used Astrodon MMOAG Monster Off-Axis Guider-One Port - UT-11731 - SOLD

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  • $699.00
  • Regular price $875.00


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  • This is a used OAG in excellent condition
  • Uses the same light beam for guiding as seen by the imaging detector
  • Avoids potential differential flexure in using a separate guide scope
  • Guides your system with unfiltered light in FRONT of your filters
  • Use a variety of guide cameras with different detectors, resolutions and sizes


Used Astrodon MMOAG Monster Off-Axis Guider-One Port - UT-11731 - SOLD

Astrodon MonsterMOAG Thin Off-Axis Guider w/ 1 Port

The MonsterMOAG is the latest innovation from Astrodon in off-axis guiding (OAG) equipment. A modular manual off-axis guider that allows you to add up to 4 prism and focuser port assemblies. Expand your guiding field of view for the ultimate in accuracy. This MMOAG includes one prism/focuser assembly and has three additional ports to add additional assemblies.

  • Smallest backfocus 1.25"
  • Solid body for no flexure
  • Large central opening of 2.55"
  • Use with large CCD cameras (KAF16803, KAF9000)
  • Helical focuser for easy focus
  • Interchangeable short 1.25" nose piece holder included if helical focuser is too tall to come to focus
  • Spacers to place pick-off optic further into the light beam
  • Dovetail connectors - rotate and lock - to align guide camera with imaging camera and telescope
  • M/F AP 2.7"-24TPI dovetail connectors provided
  • 3" male connector optional for direct connection to new, large filter wheels.
  • All parts CNC machined with low reflectivity inner surfaces

Off-axis guiding (OAG) has several advantages:

As a result your guiding becomes easier:

  • Find more guide stars
  • Do not worry about different guide exposure times among different filters
  • Allow you to follow any mirror wobble in SCTs compared to a separate guide scope
  • Eliminates a separate guide scope and its mounting/flexure issues

Take a look at the image above. On the left is a side view on the MonsterMOAG with its helical focuser, showing the male and female dovetail connectors in place and the width of 1.25". The tapped holes in the side accept strong 1/4-20 bolts that can secure steel lanyards to your camera and prevent it from falling to the ground.

The right side of the image shows the Astrodon MonsterMOAG on the new Takahashi FSQ-106ED with an SBIG STL11000XM camera and an SBIG STL-remote guider atop the MonsterMOAG.

Most importantly, the Astrodon MonsterMOAG was designed for the new, large imaging detectors (Kodak KAF16803 and KAF9000) with their 36 x 36 mm square size and a 52 mm diagonal. There is sufficient room even with faster optics to use the MonsterMOAG with common AP 2.7" threaded connectors and extension tubes without significant vignetting the imaging detector.

For those with smaller detectors, such as the 24 x 36mm KAI11000 interline CCD, the pick-off optic can be placed further into the light cone with extra spacers supplied with the MonsterMOAG.

It is important to realize that the placement of the Astrodon MonsterMOAG, or any OAG, in the optical train must be carefully considered in advance. The distance between the pick-off optic and the focal plane of the guiding camera (A) in the above schematic must be equal to the distance between the pick-off optic and the focal plane of the imaging camera (B). Place the MonsterMOAG too close to the imaging camera and the focal point may move from above the focuser down into the body of the focuser. In this case we can offer several solutions. The helical focuser can be removed (unscrewed) and replaced with a shorter part (provided). This brings the guiding camera up to about 0.9" closer to the pick-off optic. Focus adjustment is manual in this case, but it may be the only option.

Another option is what we use for the MOAG-A sandwiched between the SBIG AO-L and STL camera. The MOAG-A is so close to the STL's focal plane that focus occurs just inside the top of the helical focuser. Thus, we supplied a slow plano-concave lens (-250 mm focal length) with the MOAG to act like a Barlow lens to bring the focal plane above the focuser. This is placed in the top of the body of the MOAG-A. The same lens (optional) can be placed in a shallow counterbore on the top of the MonsterMOAG at the bottom of the helical focuser.

Lastly, an easy solution is to put a spacer, such as a 0.75" AP (Astro-Physics) extension tube (or longer) between the MonsterMOAG and the CFW/CCD. For this reason, you will need to know the backfocus distance of your CFW/CCD system and plan in advance to purchase other parts if needed.

Standard connectors (shown in the "images/articles" tab to your left) are included with the MonsterMOAG. The male 2.7" connector is placed on the telescope side. The other part faces the camera. It accepts 2.7" male threads on the ID but has 3"-24 threads on the outer diameter. You can see the dovetail that fits into the MonsterMOAG body in these parts. In this case, you must supply a connector from your CFW supplier with male AP 2.7" threads.

The four 8-32 set screws on each raised flange coming out of the MonsterMOAG press into the dovetail and pull the connector flat into the body of the MonsterMOAG to eliminate and tilting of your camera system. This also allows you to rotate the part screwed into the connector relative to the MonsterMOAG body and then securely lock it in place.

The new, large filter wheels housing Astrodon 50mm square filters for the KAF16803 and KAF9000 CCDs all have 3"-24 threaded openings on the telescope side, including:

  • Apogee Instruments AI-FW50-7s
  • Yankee Robotics Cyclops
  • Finger Lakes Instruments CFW-4-5 or - 7

Of course, the large opening of the MonsterMOAG is also useful for the KAF6303 and KAI11000, as found in the SBIG STL6303 and STL11000.

Astrodon optionally supplies a dovetail to 3" male connnector that is 0.75" long for direct connection between the MonsterMOAG and the above CFWs.


Warranty90 Day


  • Astrodon MMOAG body


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