As is often the case, a simple “I think I’ll make this little modification to my outfit” turned into “What was I thinking?” My primary goal was to add a calibration light source to my LowSpec. How hard could that be? In the end, I redesigned my LowSpec to enable a dual light source, for use with calibration sources or a flatting source and a calibration source. I also implemented grating angle automation, and used a ZWO helical focuser rather than the fiddly focuser in the LowSpec design. I wrote the software for Arduino control of the hardware, and a python program to allow me to operate the whole thing from my laptop. In the meanwhile, the mount decided it didn’t want to recognize the declination axis anymore, so the mount went back to the manufacturer for an overhaul. As I readied for what I thought would be the final system test, the telescope itself decided to go haywire, so I ultimately had to tear the telescope down and rebuild it. Now, finally, I’m back in business, and I thought maybe someone on the forum might be interested in what I did.
I used a custom-ordered “neon light” gas tube, with 80% Argon and 20% Neon as the calibration light source. It is excited by a 3Kv power supply, and is completely enclosed so there’s no possibility of high voltage leaking to anywhere it can do harm. Including that light source was quite complicated, as even a tiny leak could fry thousands of dollars worth of equipment, let alone it could fry ME. I experimented with MANY different designs and arriving at the final design was one of the most time-consuming phases of the project. In the end, the containment works very well and also prevents the leakage of stray light from the lamp.
The light is directed onto the slit by a mirrored shutter, which is opened and closed by an externally mounted servo like the mirror in a Single Lens Reflex camera. (I might have drawn design inspiration from that obviously time-tested design.) The second shutter is not mirrored and is very handy for shooting darks. Eventually I will place a halogen bulb in an enclosure on the second light port, and the solid shutter will serve the additional purpose of diffusing the flatting lamp. I’m looking forward to having flatting capability.
The grating is rotated with a stepper motor and a 1/32 microstep controller. I feel like I went way overkill with the stepper I chose, but the same stepper is used in many 3D printers, so it is easily available and does the job. As I’d never worked with stepper motors before, it was a lot of fun learning how they work and how to control them. As a result, positioning is nicely repeatable, which will allow me to build up a reference spectrum calibration library.
On June 19, a full year after i took the old LowSpec off the telescope, and a year and 8 months after I began the design of the new calibration capability, I acquired my first spectral image. I’m pretty proud of myself!