How do I focus the guide camera with the QHYCCD OAG?
The QHYCCD OAG has an integrated helical focuser. First, loosen the locking thumbscrew. Then, rotate the focusing ring until your guide stars are sharp. Once you have achieved focus, gently tighten the thumbscrew to lock the position. Avoid moving the focuser while it is locked to prevent damage.
What are the advantages of the QHYCCD OAG over a separate guidescope?
An Off-Axis Guider offers two primary advantages over a traditional guidescope:
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Eliminates Differential Flexure: The OAG uses the main telescope's optics, so the guide camera and imaging camera see the exact same field movement. This removes tracking errors caused by the guidescope's mounting rings or focuser sagging relative to the main telescope.
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Reduces Weight and Complexity: It replaces an entire secondary telescope, reducing the overall payload on your mount and simplifying your setup.
How can the QHYCCD OAG help when imaging with my 11" SCT?
Schmidt-Cassegrain telescopes (SCTs) can suffer from "mirror flop," where the primary mirror shifts slightly during tracking, causing image drift that a separate guidescope cannot detect. Because the QHYCCD OAG picks off light *after* it has reflected off the primary mirror, it sees and corrects for this mirror movement, leading to significantly sharper long-exposure images.
Which QHYCCD OAG model (S, M, or L) should I choose?
The correct choice depends on the back-focus requirements of your specific imaging train (camera, filter wheel, and corrector/reducer). Each model has a different thickness. You should choose the model that allows you to place your main camera sensor at the precise back-focus distance specified by your telescope or flattener optics.
Can I use the QHYCCD OAG with a full-frame camera and a fast f/4 Newtonian?
Yes, but careful placement of the prism is key. In fast optical systems, the prism can cast a shadow on the main sensor if placed too far into the light path. You should position the prism just outside the field of view of your main imaging sensor to pick off guide stars from the edge of the corrected field without creating vignetting.
What kind of guide camera works best with the QHYCCD OAG?
A sensitive, monochrome guide camera with small pixels is ideal. Models like the QHY5III series are excellent choices. Their high sensitivity allows them to detect fainter guide stars in the small field of view provided by the OAG's prism, which is especially important at long focal lengths or when imaging through narrowband filters.
