Artifical Star

Artificial Star

I present here details of how I 'constructed' an artificial star to collimate my LX200.

[Click on the images below for a larger 640x480 version]

	First I obtained a short length of fibre optic cable, it was used as a patch cord on some network switches. These standard short wavelength cables usually have a 62.5µm diameter core. By using a full cable length you retain the connectors and the 'polished' cable ends, if you cut the cable then it will probably still work but you will have ragged fractured ends and the light may not be emitted as evenly.
	The cable came with some flexible rubber protective 'caps' over the ends of the fibres. Keep these - they are useful!
	The light source is simply my white LED torch. I cut the end off one of the protective caps so I now had a tube. Simply push one end of this tube over one of the LEDs in the torch, then push the fibre optic cable into the other end. Viola - you have now coupled the fibre to the LED. This photo shows the arrangement, you can see the light coming out of the other end of fibre in the larger picture.
	To use the assembly as an artificial star, I simply push the free end of the fibre cable through the bottom of a cardboard box, and put the torch behind the box. The box acts a bit of light shield and keeps the 'star' in semi-darkness. I find that at night the torch only needs to be raised to about half brightness to be effective.
	How far away do I place the star? Well the maths using Dawes limit suggests that a 62.5µm source needs to be 25m away for a 250mm diameter objective (0.5 arc-secs) I use a effective eyepiece focal length of about 4.5mm (9.4mm + 2X Barlow).