For more information about the pros and cons of off-axis guiders versus guide scopes, see the following:
Chris Vedeler’s Guiding Tips With an Autoguider on a Schmidt-Cassegrain.
An opposing viewpoint is Phillip Perkins’ Off-Axis Guiding post.
For a good summary of the issue, see the end of Greg Hartke's Guide Scope Focal Length Calculations post. Also, peruse the rest of those MAPUG threads for more information on each opposing viewpoint.
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