DIY Artificial Star

[tempestwizz]

As part of the re collimation of my TOA recently, I needed a fixed star in a convenient location. After looking at some you tube offerings I decided to make my own.
Fibre optic cable has a pipe size of about 64 microns. I used a spare fibre cable I had lying around with ST connectors. The ST neatly push into a 2.5mm hole.
In an off cut of rectangular aluminium I had lying around also, I drilled a 2.5 mm hole in one side, and a 5 mm hole in the facing side. I pulled a white LED out of a defunct Aldi torch and stick it in the 5mm hole.
For power I was going to use a 12 volt battery I also had laying around. Given about a 2 volt drop across the LED, I needed a resistor to absorb the other 10 volts (ish). For an anticipated current of about 10 mA that would need a 1k ohm resistor. I found a 1.2k ohm, close enough.
With power connected to the LED via the resistor (and the correct way round so that the LED lights) I plugged one end of my fibre into the other side.
At the far end of the fibre, I had a bright pinpoint light source.
I drilled a 2.5 mm hole in some timber which I made fit inside some plastic pipe and put it on a spare tripod. Plugged my lit fibre into the hole, and voila, an artificial Star.
For a 130mm aperture system, It seeds to be at least 10 metres away to fall under the Raleigh limit for Star size.
Thought I’d share, and see if I can post pics.

Brian

[Atmos]

That’s pretty cool, the kind of thing I may find myself needing to make at some point.

[skysurfer]

Can be even easier as 2.5mm is way too large and the star is at 10 meters brighter than Venus.

Paste duct tape over the LED, or use a short PVC tube in which you center the LED and paste duct tape over the end of it which is facing you(r telescope).
Pinch a very small hole with a needle in the center of the duct tape cover and ready.

[tempestwizz]

The 2.5 mm is the size of the fibre optic connector nose, not the diameter of the ‘star’. The Star diameter is constrained by the diameter of the light conducting section within the fibre itself. Depending on the type of fibre it is usually either 50 microns or 64 microns I think. The actual fibre is thicker at around 120 microns, but the outer jacket does not transmit the light.
I think the fibre size is probably more repeatable than a pinprick in some obscuring media. Also the fibre is quite flexible and lightweight for placement. For another also, the ends of the fibres in the connectors are polished providing an even and scrambled light source from the 64 micron hole. The polarisation and othe phasing oddities that may arise from a close sourced LED are not so predictable. After a few metres travelling down a fibre, all or any of the odd modes are smoothed out.
Cheers.

[Martin_S]

i went the lazy way and placed a glass ball off my xmas tree on a fence post and used the suns reflection for my 6"sct then finished of at night with a star test

[tempestwizz]

Yes, that’ll work too, but in my case my scope was fixed on a bench so that I could could work comfortably and without too much movement during adjustment. Also so that I could work in the subdued lighting of my closed workshop to minimise any off axis light dilutingwhat already dim airy disc rings I had. I arranged for the Star to move into my desired position rather than point the scope at a static target. Whatever works for your situation is fine.