Astrodon introduces the MOAG™, Manual-Off-Axis-Guider, a unique off-axis guider for astrophotograpy. It's design was patterned after the ROAG , Rotating-Off-Axis-Guider, which was introduced in 2005.
The stand-alone version also comes with two v-groove adaptors. The adaptor on the camera side takes up 1/2" of backfocus and has female 2.7" AP threads (24 TPI). The adaptor on the telescope side takes up almost no backfocus and has male 2.7" AP threads. Thus, the stand-alone MOAG integrates nicely with any 2.7" system, such as found on the back of most RC telescopes. Other adaptors are available from Astro-Physics to convert from AP 2.7" threads to SCT threads on the telescope side.
The v-grooves are important. They give you additional flexibility to adjust the angle of the MOAG relative to your telescope and CCD camera.
A larger stand-alone version (MOAG-L) will be available at the end of November, 2006 for the new, larger CCDs (KAF9000, KAF16803). The MOAG version shown here will work with CCDs the size of the KAI11000XM and smaller.
The distance between the pick-off optic and the focal plane of the guide CCD must be identical to the distance between the pick off optic and the focal plane of the imaging camera.
This distance will vary due to the use of different imaging cameras, filters wheels and other accessories, such as in-line focusers.
Let's say the MOAG is placed next to the camera and the focal plane for the guide CCD is too close to the pick-off optic. In this case, a lens (such as a plano-concave lens) will be used in the MOAG to extend the focal distance and place it within the adjustment range of the helical focuser.
Conversely, if the MOAG is placed much further away from the imaging CCD focal plane, another lens (such as a plano-convex lens) may be needed to bring the focal point closer to the pick-off optic. However, in this case, you can always pull the 1.25" further up in the helical focuser, or use an optional eyepiece extender provided by Astrodon.
When you order you will be able to use the following chart to select the lens needed for your system if you need one. These will come in a screw-in holder, very much like a filter holder, thereby making replacement easy if your needs change over time. The order code then would become MOAG_-250 for a standalone MOAG with a lens suitable for a short focal distance of < 65 mm, for example. Your MOAG will come equipped with a lens and lens holder if you specify that you need one in your order.
|Focal Distance||Lens Designation|
|65 - 100||0 (no lens)|
|>100 mm||+ 75|
This only applies to the stand-alone MOAG. The MOAG-A for the SBIG STL/AOL comes with a -250 mm plano-concave lens in the replaceable lens holder, since that focal distance is fixed.
MOAG FOR SBIG AOL/STL
SBIG brought adaptive optics (AO) technology to amateur astrophotography to assist guiding, by "wiggling" an optic several times a second, and only "bumping" the mount when there is a significant deviation. Adaptive optics can reduce the size, measured as FWHM (full-width at half-maximum intensity), of stars by perhaps as much as 0.5 arcseconds, depending upon the seeing conditions. This becomes significant at longer focal lengths for high resolution astrophotography.
SBIG AO technology was designed for use with their internal guide CCD contained in the imaging camera. Thus, a major disadvantage is AO guiding through RGB and narrowband (H-a, SII, and OIII) filters. Finding a guide star without AO optics for the internal guide CCD is often times a challenge. AO guiding makes that even worse or impractical.
The version of the MOAG that integrates with the STL/AOL now provides you with the opportunity to guide in front of your filters, potentially increasing signals over RGB filters by a factor of 3 and over an H-a filter by a factor of >100.
The left figure below shows the MOAG-A configured between the SBIG STL/AOL. Light comes from the telescope off from the left, passing throught the transparent AOL movable optic, through the MOAG-A and into the STL camera. The AOL screws into the MOAG as it would into the STL. The MOAG-A included a special adaptor with 2" male threads that screw into the STL nose piece. It has a V-groove that fits into the MOAG-A and is tightened down with 4 set screws. In this way, the AOL/MOAG can be rotated to the vertical position shown below and locked into place. A variety of adaptors can then be used to connect the assembly to the telescope. In this case, an STL-to-APmale adaptor is used to screw into the back of a 12.5" RCOS telescope using 2.7" AP tubes, shown lower right.
The MOAG takes up 2" of backfocus and the STL v-groove adaptor takes up another 3/8".
A pick-off optic extends into the internal opening of the MOAG-A from the top. It is attached to a plate that contains a screw-in holder for various beam reduction/extension lenses. A BORG helical focuser is secured into this plate that holds the guide CCD with a 1.25" nose piece.
This image shows active AOL tracking of a very bright guide star, Scheat, in Pegasus with the MOAG-A on the 12.5" RC shown above. MaximDL v 4.55 was used. A track time of 0.1s was used, resulting in a guide rate of 6.9 Hz.. Click on image to enlarge.
This image shows active AOL tracking of a very bright guide star, Scheat, in Pegasus with the MOAG-A on the 12.5" RC shown above. MaximDL v 4.55 was used. A track time of 0.1s was used, resulting in a guide rate of 6.9 Hz..
Click on image to enlarge.
A 1 minute image taken with a green Astrodon filter using this AOL guiding configuration resulted in a FWHM of ~1.8 arcseconds that night.
The MOAG in many cases makes narrowband AO imaging possible. The image of M33 below show a 10 min (uncalibrated) exposure using the STL11000M and a 6 nm Astrodon H-a filter guided with the MOAG-A and AOL on a magnitude 8.1 guide star. The guide exposure was 0.2s and the guide rate was 4.3 Hz (click on image to enlarge).
Once the location of the guide star is mapped, data acquisition programs can potentially find guide stars automatically during sequences or after meridian flips. The following screen capture from Software Bisque's TheSky6 shows the location of the guide star used for the above H-a image of M33 with the MOAG-A. It is near the center at the bottom with the red circular target.
MOAG-ST for SBIG ST Cameras and AO8
The MOAG-ST works just like the MOAG-A, but is designed with a dovetail connector having SC (42 mm) thread for the SBIG CFW8, CFW9 and CFW10 or any of the ST cameras.
MOAG-A, MOAG-ST $780