PerfectStar Focus Motor for SCT

perfectstar_sctThe PerfectStar Focus Motor for SCT is designed to provide precise control of focus with Schmidt-Cassegrain Telescopes (SCTs).  Although intended specifically for use with the PerfectStar Focus Controller, the motor is also compatible with controllers from many other manufacturers.  

The standard mounting for the PerfectStar motor works well for most refractors and Newtonian reflectors, but required customization to work with the typical SCT focus mechanism, which works by moving the primary mirror rather than moving a draw tube.  With the PS SCT Motor it is now very easy to install a focus motor on an SCT.

The motor is enclosed to protect the motor from dust and moisture. Likewise, the aluminum mounting collar encloses the focuser shaft to prevent dust from getting into this sensitive mechanism.  Connectors are mounted on the enclosure body for the controller connection and for the optional temperature sensor.

There are 2 different versions of PS SCT; one for scopes of up to 8” aperture and one for larger models.  The smallperfectstar_sct1er version uses the same motor as PerfectStarLite, while the larger version uses a Hurst motor.  The motivation for having 2 sizes is that the motor assembly must be kept as small and short as possible to avoid interfering with the camera and other parts of the optical train.  Since the SCT focus mechanism provides a large mechanical advantage (and a very predictable load on the motor), it is possible to use the smaller motor with smaller telescopes, where the physical size is most limited.  For the 8” EdgeHD, the motor is just 3.5” in length and easily clears typical cameras, with or without the focal reducer.

PS SCT is designed specifically for the Celestron EdgeHD series, but most SCTs use the same focus mechanism and it is likely that other models from Celestron are directly compatible.  SCTs from other manufacturers can often be fitted with minimal customization.

perfectstar_sct2Installation of PS SCT on an EdgeHD telescope is very simple:  The rubber focus knob is pulled off from its sleeve, exposing the sleeve and the retaining plate.  The retaining plate is then removed and replaced with a bushing that will support the focus motor.  A delrin coupler is then attached to the sleeve and the motor slides over this assembly, attaching to the bushing with thumbscrews.  The thumbscrews make it easy to remove the motor for storage or transport, if necessary.

Other features of PS SCT are the same as for the classic PS motor, except that the motor in the smaller version is not a Hurst motor, and this is reflected in the price difference between the 2 versions.  Temperature compensation is available in either version.

The motor unit comes with a 6 foot cable to connect to the controller.  The standard cable is a flat ribbon because this provides the lowest weight and a low-profile connector, but a perfectstar_sct3standard round cable with molded connectors can also be ordered as an upgrade.



Small Motor unit:   $145  (for up to 8” aperture)
Large Motor unit:   $225
Temperature sensor:    $25

See the PerfectStar Focus Controller for details on this enhanced controller and its options.  For information on other motor options, please contact me.


Orders for PerfectStar SCT Motors are now being accepted.  The smaller version is usually in stock.  The large version may take several weeks. Orders requiring a non-standard gear reduction ratio may also take additional time and a 50% deposit to allow ordering the motor from Hurst.

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About Greg Marshall

I am a retired electronics engineer and after a few months of enjoying my leisure I began to miss doing product development. My astronomy hobby always needed new solutions to unique problems, so I decided that whenever I came up with a good solution I would try to make it available to others.

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