Locating suitable guide stars is much more difficult with an off-axis guider than it is with a separate guiding telescope.Ĭareful planning is needed to ensure suitable orientation of the pick-off prism and imaging camera to get a guide star in view. To control the AOG you need to attach a fast frame-rate camera, in addition to your imaging camera.įinal accurate focus of both cameras was achieved by focusing the imaging camera using a Bahtinov mask and the scope’s focuser, and then accurately focusing the guide camera using the fine adjustment on the AOG. Generous length cables are supplied for power, USB 2.0 and ST4-mount-compatible guider connections, and the whole outfit is supplied in a padded hard case. We noticed a distinct ‘droop’ in the optical train using the supplied 2-inch nosepiece with our Sky-Watcher 80mm ED refractor, so opted to use Sky-Watcher’s own ‘T’ adaptor to ensure a more substantial mounting. There’s a good range of adaptors supplied to enable focusing using all sorts of cameras, including a 2-inch nosepiece, a male ‘T’ thread adaptor and rotation locking ring for the camera side, a female ‘T’ thread adaptor for the telescope side and 30mm, 17mm and 7mm ‘T’ adaptor extension tubes. The Orion AOG is well made from machined aluminium. Using the same telescope for this avoids ‘differential flexure’, a technical term for unwanted movement. The AOG also acts as an off-axis guider, which means that it channels light to a guide camera from the same telescope as the imaging camera, using a small prism to ‘pick off’ a sample of the view. This has some major advantages over conventional guiding, as it is easier and faster to move a small piece of glass than it is to move a whole mount.Ĭorrections are made very quickly and, with a suitably bright star, several times each second.
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