Homemade Electronic Focusers For

Obsession 20", ST80 & ETX90 Telescopes

Components come from old "Dead" CD Rom parts.

For My 20" Obsession, two 12V "Reversing" Control Boxes give me a full range of focusing control, one at the scope...as well as one 35' away...this effectively give me all the control I need while imaging during the coldest of weather.

ST80 homemade focus motor...uses the same controllers as the obsession. It's not pretty but it works great. All recent astro images were taken using these focusers.

For my ETX90, a single control box (new model like in the video) gives focusing control at up to 35' away. The old hand control unit is shown below...it is no longer used...

Meade 505 Cable for Autostar.

Homemade ETX Motorized Focuser Set. 

I made the motor assembly out of an old non-functioning CDrom drive. The motor that opened the CD tray was perfect, and it had flat sides which made mounting it easier. Mounting the motor was a simple affair. I first attached a length of thin steel (1" wide x 2.25"long) to one of the bottom mounting holes on my ETX90ra. Then I "hot-glued" the motor to the steel in the proper orientation. I wired a Female RCA plug to the motor for the control signal. Of course all motors in a CDrom drive are 12v, so I simply attached 6volts (4AA batteries) to reduce the speed and torque of the motor. The pulley already mounted to the motor was perfect (3/8"). So all I had to do was cannibalize one large plastic pulley (1.25") from the CDrom drive to affix to the focuser shaft. However, the center hole of this pulley was a little too large for the focuser shaft. I simply inserted a 1/2" length of rubber band through the pulley's hole, leaving half exposed on each side. I then slid the pulley onto the focuser shaft. It fits snuggly now. I then mounted the original ETX focus knob back on the shaft to allow manual use at any time. I am using a simple rubber band for a power transfer belt...however, I spent a few minutes trying several sizes out before I settled on one. The power supply has a 3' length of cable with a male RCA plug at the end, it attaches to the handpad (and stays warm in the house with me). The long cable is simply a 40' length of speaker wire, with a male RCA plug on each end. The handpad is a lot more complicated to explain. It contains a small circuit I designed to reverse the polarity of the motor according to my handpad commands. I should add that it has no switches or electronic components. I actually used small incredibly thin strips of springy steel and arranged them to contact solder points located beneath the steel strips. 2 steel strips per function (focus in, focus out). Smooth, flexible plastic covers hover above the springy strips and save your thumb from pain. When you press either function you are depressing two springy steel strips onto two solder points, completing the circuit, and making the motor turn forward or backward. I have used this motorized focuser for 5 months now and my pictures speak for themselves. The focuser responds like this: A tap on the "Focus In" button produces a quick burst about the equivalent of 1/2 of a knob turn...while a tap on the "Focus Out" button produces a very small "micro movement" perfect for fine focusing. It works flawlessly...all while I sit in my warm house...and this is priority #1 if you live in the northeast like I do.