PerfectStar B Focus Controller

Building on the success of the classic PerfectStar Focus Controller, PerfectStar B (PSB) is the next generation controller, with enhanced speed, torque, and programmability. It is also a step up in production quality, featuring metal construction, engraved labeling, and better cables and connectors.

But the essence of PSB is its support for bipolar stepper motors. The classic PerfectStar, like most focus systems until now, uses unipolar stepper motors. Unipolar motors were probably originally chosen because they require less sophisticated electronics to drive them. But bipolar motors offer many technical advantages, and since they are now widely used in many areas, highly integrated driver chips are now readily available.

Bipolar motors are inherently more efficient than unipolar, both for a given size and for a given power consumption. That is, they provide more torque in comparison to an equivalent unipolar motor. But the big advantage comes from using a more sophisticated driver chip. In focus control systems using unipolar motors, the motor windings are simply switched on and off in a defined sequence, with no regard for signal integrity. The step rate is therefore limited by the need to let the signal settle after each switch. The driver chip in PerfectStar B actively monitors and controls the current flow to suppress “ringing”, which allows for much faster step rates.

The result is that at medium and fine focus speeds, PSB delivers focuser movement with no lag. Turning the knob on the handset is just like turning the knob on the focuser itself, except that it moves in precise increments, and without vibrations.

PSB also gives the user more control of the motor drive parameters. In addition to selecting the step period, the user can specify the drive current for both moving and idle stages. Therefore, you can optimize control for either speed or torque, and optimize braking for strength or power consumption.

Moving to bipolar motors is the right move for the future, but it also brings freedom from the compatibility constraints of older focus systems. In particular, the connections for unipolar motors typically use ribbon cable, which is not really a good choice for this application, but is dictated by mechanical constraints of the DB-9 connectors of this defacto standard. PSB uses modular connectors and standard ethernet cables, which are readily available in a variety of lengths, colors, and special features such as shielding.

PerfectStar B Features:

    • Direct USB connection (ASCOM driver included)

    • Manual control via multi-speed knob (focus by wire)

    • Four “speeds” (coarse to fine focus)

    • Backlash compensation

    • Temperature compensation

    • Auto-focus (with 3rd party software)

    • Recessed LED status indicators

    • Motor braking to hold position

    • Programmable step rate

    • Field flashable firmware

    • Programmable drive current

    • Programmable braking current

    • Faster step rates (no lag at fine and medium speeds)

    • Metal enclosures

    • Coiled handset cable

    • Option connector for future enhancements


    • PerfectStar B motors are available for many telescopes. They use the same type of coupling/mounting as classic PerfectStar motors

    • The PSB controller is also compatible with bipolar motors from select vendors

    • PerfectStar B is NOT compatible with classic PerfectStar motors or other (3rd party) unipolar motors, although support for such motors may be added in the future as an option.  

Pricing and Availability:

The PerfectStar B controller is available now.

  • PerfectStar B Controller:   $229
  • AC Adapter:                      $20
  • DC Power Cord:                $15
  • 2m USB cable:                   $5
  • 5m USB cable:                  $10


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.

Leave a comment