"PerfectStar" Focus Controller

[Greg Marshall]

Astro photographers all know that perfect focusing is both essential and difficult. A motorized focuser is a big help because it allows finer control while avoiding the vibrations typically induced by turning a focus knob by hand. However, simple DC motor systems cannot provide enough precision and absolute positioning systems using stepper or servo motors are usually very expensive.

To solve this problem at Wa'chur'ed Observatory I developed the PerfectStar focus controller and now offer it to you. PerfectStar supports stepper motors for absolute position control in both manual and computer-driven focus control. The motor interface is compatible with Robo Focus units, which means that it can be used with motors provided by Moonlite focuser and others. The functionality is basically the same as Robo Focus and others, but with some enhancements:

* Direct USB connection (no COM port to select and keep track of)
* Temperature sensing at the telescope rather than inside the controller
* "Virtual Focus Knob" for manual control that works like a 3 speed focuser

An ASCOM-compliant driver is included to provide computer control, including auto focusing and temperature compensation (using 3rd party application software). Temperature compensation measures the ambient temperature (at the telescope) and adjusts the focus position to keep your image in perfect focus as the temperature changes.

The Virtual Focus Knob (on optional hand controller) is different from most focus controllers. Rather than requiring you to control the movement by how long you depress a button, you simply turn the knob as if it were the focus knob on the telescope. The difference is that this knob has "detent" positions corresponding to specific step counts, so you know exactly how much you are changing the focus position. Three speeds are available: 1, 5, or 25 steps per detent.

PerfectStar also has programmable backlash compensation to maintain precise position control even when changing direction. Auto focus software generally avoids this issue by always approaching from the same side of optimal focus, but with PerfectStar's backlash compensation you can adjust focus (either manually or through a computer) without worrying about backlash.

One advantage of a stepper motor is that it "holds" the last position by leaving one of the motor coils energized when not moving, so focus will not slip as the telescope angle changes. However, PerfectStar allows you to manually lock the focuser and de-energize the motor to save power and avoid trying to move the motor while locked.

With the basic controller you can use a 3rd party focus motor (Robo Focus compatible), provide your own motor, or I can help you configure a motor with mounting and coupling hardware. To keep the price low, I offer the controller with just the essential components; the controller, a 12V power cable, a USB cable (6 feet), motor cable (6 feet), and software CD. This basic package is priced at just $100. Options are:

* AC adapter $15
* 16 feet USB cable $10 (instead of the standard 6 feet cable)
* Hand controller $25

Note that the temperature sensor is part of the motor assembly and is included when I put together a motor kit for you. I can also work with you to provide temperature sensing with any motor choice. I do not have a fixed price for motor kits because they vary with the installation and are quoted to your request. Typically, a complete motor kit is less than $100.

Thanks for your interest and please contact me with any comments and questions. I am announcing PerfectStar here on AstroGab first in hopes of getting your feedback before making a more public announcement.

Clear Skies,
Greg
Wa'chur'ed Observatory