This is a unit that attaches to the back of a SCT, and has a draw tube that moves in and out to achieve fine focus. My complaint with zero shift focusers currently available, is they are designed for use with a person at the telescope. My long term goal is to operate the telescope and peripherals from inside my house via a computer link. To that end I have started on a zero shift focuser that is controlled by an Intel 80C196 micro-controller. While using the zero shift focuser at the telescope, the observer will be able to use many of the same functions, with position being shown by an LED display.
Actual movement is provided by a small dc motor with internal and external gear reduction.
The motor also has an optical encoder integrated into it that is used for position detection. I hope to finish this project during 2000-2001. Another change may also be in the works as well. An email in the ATM mail-list gave a URL for a site where Don Clement is building a Cassigrain. He shows a zero shift focuser of a unique design.