PerfectStar Focus Motor

perfectstart_focus_motorThe PerfectStar Focus Motor is a premium stepper motor designed to provide precise control of focus with many types and models of telescope.  Although intended specifically for use with the PerfectStar Focus Controller, the motor unit is also compatible with controllers from many other manufacturers.  

Based on a top-quality stepper motor from Hurst, it provides the reliability and precision needed for demanding astrophotography applications.

The motor is enclosed to protect the motor from dust and moisture. Likewise, the aluminum mounting collar encloses the focuser shaft (and reduction mechanism where present) 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.


Basic features include:

12V Unipolar stepper motor and gear reduction from Hurst Motors
Low backlash (remaining backlash is compensated out by the controller)
Industry standard DB-9 motor connector
3.5mm phone jack for optional temperature sensor
High impact plastic enclosure protects from dust and moisture
Aluminum shaft enclosure supports motor and protects focuser shaft and reduction mechanisms
Two-piece shaft coupler allows easy attachment to many telescopes
Thumbscrews for fast and easy connect and disconnect

The aluminum mounting collar is the only part that is significantly customized for a particular model of telescope (one piece of the coupler is also drilled to match the shaft diameter for your scope).  In the typical case, installation is simply removing a focus knob (two knobs for a dual-speed focuser), attaching a coupler to the focuser shaft in place of the knob, positioning the motor unit over the end of the focuser shaft, and tightening the thumbscrews against the bell housing of the focuser shaft.  Not all focusers have a suitable bell housing, but many do, including Feather Touch (and the Feather Touch-supplied mechanism on Astro-Physics scopes), William Optics refractors, and Astro Tech refractors, to name a few that have actually been used with the PerfectStar Motor.  For SCT use see PerfectStar SCT.

When a dual-speed focuser is used the motor can couple to either the fine- or coarse-focus shaft (with appropriate selection of the motor gear reduction).  Using the fine-focus shaft is preferred on top-quality focusers such as the Feather Touch because it provides near zero backlash.  However, with some focusers there is too much slippage in the fine-focus reduction, so coupling to the coarse-focus shaft is recommended to provide accurate absolute position performance.

Every PerfectStar Motor includes a 3.5mm jack for a temperature sensor, which is needed for temperature compensated focus operation and recommended for all installations unless you already have a means of reading the temperature at the telescope.  The temperature sensor is a small copper tube with a 3.5mm phone plug on one end.  It can be plugged directly into the PerfectStar Motor unit or you can use an extension cable (an ordinary stereo audio cable with 3.5mm plug on one end and jack on the other) to allow placing the sensor on the telescope tube itself.  The sensor has a resolution of better than 0.1C and an absolute accuracy of 0.5C.  Temperature compensation keeps the telescope in perfect focus by adjusting the focuser position to compensate for the small amount of change in the telescope tube dimension as the temperature changes.  For most accurate results, use the extension cable to place the sensor in contact with the telescope tube.

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 standard round cable with molded connectors can also be ordered as an upgrade.


Motor unit:   $195  (includes flat ribbon motor cable)
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 Motors are now being accepted.  Units for certain popular focusers may be in stock, but in most cases it will require fabricating the mounting, which 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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