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The extension sleeve fits between the telescope and the focuser and fits the GSO RC telescope's 2” Crayford focuser.
GSO RC telescopes have a long back focus which allows the use of off-axis guiders and systems to reduce the focal length. However, this long back focus can also be problematic in many cases. The focuser has to be fully extended and even then extension sleeves have to be used, too. This is neither an optically nor mechanically recommended solution.
The extension sleeve’s advantages are clear. The focuser is always in an optimal position. There is no interference caused by levers being too long. The illumination is also better as the extension sleeve's free bandwidth is significantly greater.
