There are plans for one design here:
http://www.iceinspace.com.au/index.p...63,265,0,0,1,0
I'm in the process of designing and building one of my own. I have yet to test it, but it should give me a 0.16mm "star" if I mount a 9.7mm eyepiece on the front of it. At the present it consists of a point to attach a light source (LED torch), a 5mm aperture, 30cm baffled tube, and eyepiece mount. The 300mm tube combined with the 9.7mm eyepiece gives a 31x reduction in the angular size of the 5mm hole. At a distance of 80m, it should provide an angular size of 0.44", which is under the resolving limit of my scope. The real question is if the magnitude will be adequate. My torch has multiple brightness levels, so I'm hoping one of them will work.
I may build a second one using a 5mm high intensity green LED for star testing purposes. The other option would be a green filter on the eyepiece, but that would require me to change the way that I am mounting it on the tube.
The plus side to this design is that it should be usable over the FOV of the eyepiece, in this case a 50 degree Plossl. Some designs I have seen would have a very narrow usable field, or require some specialized parts to build. I don't happen to have any 0.0625mm fibre optics around (or maybe I do?), so I decided to roll my own.
Regards,
Eric