Review of RigelSys Electric Focuser
by Charles Hall
If you've never used an electric focuser you're missing a real treat. An electric focuser will bring you both features you expect and some wonderful surprises. The primary benefits of an electric focuser are:
1) Fast, effortless focusing
Especially if you have an SCT, you may have to turn the focus knob what seems like hundreds of turns to attain focus, especially when swapping in and out a DSLR for a webcam. In fact my SCT focus knob acts so slowly it's sometimes very hard to tell what direction to turn to bring it into focus.
2) No vibration.
This is the unexpected benefit. Despite the fact that the little electric motor is buzzing and vibrating, the image through the eyepiece remains perfectly steady. With manual focusing you touch the knob, wait for the image to steady, touch the knob again, etc. There is NONE of that with an electric focuser. I guess because it's hanging off the telescope some law of physics cancels out the motor vibrations.
3) Optional remote control.
It goes without saying that without an electric focuser, you cannot implement full remote control of your telescope. I had a Meade 1244 focuser jury-rigged to my SCT and it plugged in directly to the Meade mount and the buttons on the handbox (or RS-232 connection) could control the focus. Since upgrading to the RigelSys system I have the option of a USB connection.
I only gave up on my Meade 1244 lash-up when I got tired of having no idea where I was in the focusing range. Unlike a refractor, my Celestron SCT gives no outward clue of where the focus is its travel: all the way in? all the way out? (It turns out that when you remove the focuser knob and look down the hollow shaft there is a moving threaded rod which moves in and out, but it's not practical to use that as a guide.)
Enter RigelSys. RigelSys offers a somewhat bewildering array of focusing gadgets. In particular they had a version that was a custom fit on my Celestron SCT. They offer two basic motor types, the first is a simple DC electric motor, the second is a stepper motor. In theory the stepper motor insures exact, repeatable control. Both are controlled with a "step" and "step size" signal from the controller, but it's ultimately analog on the non-stepper version.
MOTOR: I went with the cheaper non-stepper version. It bolts on to the Celestron easily. You do have to remove the existing focus knob, which you can replace with a rubber crutch tip if you wish. To focus manually (I *never* do this) you can loosen a single thumbscrew and the motor assembly springs out of the way.
DC CONTROLLER: The "nFOCUS" controller for the motor is a little black box with a light, an on/off switch, and two big buttons. There's also a socket for the motor cable and two fine adjustment controls (which I don't touch). It takes three AA batteries, which seem to last a very long time.
To use it you press one big button to focus IN, the other big button to focus OUT. While moving IN or OUT, you can then press the second button as well and the speed increases dramatically. In practice this motion is very easy and intuitive, you rest two fingers on the two buttons and you have total control. I just leave the controller hanging in the air by its cable until I need to adjust focus.
USB INTERFACE: I also bought the "usb-nFOCUS" interface. It connects to the "nFOCUS" controller via a coiled cable and also has a USB connector and a temperature sensor. Once installed on your PC, the "GCUSB nFOCUS" app not only shows you a relative indicator of where you focuser is set but also allows automatic temperature compensation. It is ASCOM compliant and is your gateway to other ASCOM programs. However if you use both the manual buttons on the controller at the same time as the USB interface the position indicator on the PC screen will no longer be in sync.
I thought I would use the USB interface a lot, but in practice I don't. Maybe I learned my lesson about trying to image with too many devices in a single night and my life has simplified.
RigelSys also includes some information about a free automatic focussing app called FocusMax that works in conjunction with your imaging device. I haven't tried that yet.
I find an electric focuser to be indispensable. The RigelSys offerings are an excellent solution. The more sophisticated stepper motor version offers even more precision, but as you can see from my review the more basic motor and its hand controller more than meet my needs. With the usb-nFOCUS interface I am also ready for the next step, whether it be remote control, temperature compensation or fully automatic focusing. It doesn't hurt that Leon Palmer of RigelSys provides excellent customer support and that the stuff he sold me has been totally trouble-free!
This setup costs me $235 ($185 for the motor and controller, $60 for the USB interface). The stepper motor and controller (usb-nSTEP) would have been from $65 to $175 more depending on options. RigelSys offers several bundled pricing options, so you should check their website for current pricing (www.rigelsys.com) but this gives you an idea of what you're in for.
Once you've have one of these you'll know it's money well spent!