In September of 2006 I set about making my portable astronomy setup (Losmandy GM-8 with William Optics Megrez 80 and SkyWatcher guide scope) more successful. One of the things to do this was to improve focusing capabilities when using digital cameras. Focusing even a simple camera like the Canon EOS 350D can be quite a challenge out in the field with less than ideal conditions and a medium focal length telescope. The Orion Accufocus was the path I took.
Requirements and options
When considering the focus situation I was going through many options from building my own focus motor using stepper motor, gearbox and drive kit to buying another RoboFocus.
My Meade LX200 setup uses a RoboFocus by HomeDome connected to a JMI NGF-C focuser. This works excellently without any problems at all. However it’s a little expensive to repeat in a hurry for the portable setup. Also, I liked the idea of some simplicity, not necessarily requiring all the components and cables of something as complex as the RoboFocus.
It turned out that the Orion Accufocus was cheaper to buy than I could build my own focus motor. That together with a local supplier having one in stock made the decision for me. I am unsure if there are any direct compeditors to the Orion Accufocus, I didn’t se one in my searches but I’m sure there is.
What’s different between the Orion Accufocus and the RoboFocus? Lots. Most of it obvious. The not so obvious ones are: The Accufocus does have backlash, a reasonable amount but surprisingly I haven’t found it a problem. The Accufocus runs on batteries so you need a spare on hand, but save on a cable.
Remember that whilethe Orion Accufocus is a motorised focuser solution, it is not an auto focus solution. For auto focus on a telescope you need to be able to connect the focuser to a computer, something like the RoboFocus will handle autofocus easily where as the Accufocus is not suited to this task.
A few basic stats
Cost: AU$89
Operation: In & Out buttons and speed control.
Installation: Quite straight forward depending on what you mount it on, but the motor does have convenient screws and supplied brackets.
Installation
Fitting the motor to my William Optics Megrez 80 was surprisingly easy. I cut/drilled/bent a piece of aluminium to do the job. I mount it on the base of the Megrez where the tripod plate would normally bolt on (see pictures).
The shaft size does not suit the Megrez but that was easily solved by wrapping insullation tape around the shaft until it was the correct diameter. That is a far from ideal sollution, a metal machined sleve would be much more accurate and suitable, but the tape does a suprisingly good job.
The unit comes with a little velcro to attach the hand controller somewhere. Remember to put it on/near the OTA not on the tripod where it won’t move with the OTA when the telescope slews!
Installing the Orion Accufocus on my William Optics Megrez 80 took me about 3 hours total, and I’m no expert at machining etc but can use a drill and hack saw.
Usage
Responsiveness: The Accufocus is very responsive to button presses. The buttons are easy to press for short bursts or hold down. The motor seems to have enough grunt to respond accurately.
Backlash etc: While I noticed the motor does have some backlash before I installed it, I haven’t found it to be a noticable amount in practice. I think this is largely because of the motors minimum speed still being relatively fast, soaking up the backlash without me noticing.
Speed: The motor has a variable speed dial, slow to fast. The range is not huge but is useful none the less. Slow is not as slow as the RoboFocus. Fast is faster than the RoboFocus. For fine focusing of a CCD the slow speed is almost not slow enough, you have to be very careful with your presses.
Movement: Movement is very smooth and I don’t notice any vibrations or other problems with the motor.