Here is an article that could be useful to some of you.
The advantage of having an artificial star is obvious; we don't have to wait
for good steady skies for testing our scope optics. We can test our optics
anytime, even in daylight! But problem with all the current artifical stars are
:
1) Very expensive...some sites are selling them for over US$100! That's crazyfor a point of light
2) Many propose to use silver Christmas ornaments. Problem is..you need a large field with good distance for this. And of course, you need bright sun shine. For our weather, I don't think it's fun doing star test under a hot sun.
3) The last method was proposed by Richard Berry in one of the S&T. He
suggested to use a LED light with a 4-5mm eyepiece in front of it. The output of the eyepiece will be 10-15 times smaller than the original LED depending on how far the eypiece is away from the LED. Problem is, you need to get a PVC pipe to hold the light and the eyepiece in a straight line. Simply too troublesome for people like me.
The problem with artificial star is that you need a very tiny point of light.
If your point of light is not tiny enough, then your scope need to be very far away. We all know that space is a rare commodity in Singapore, so we don't have that luxury. That's why commerical artificial star is very expensive, their light is only about 100 microns acrioss.
However, I have found a cheap method in making a very tiny point of bright light that's good enough for testing your scope optics. What you can do is use fibre optic cables. Get a short length of fibre optic cables with one end a female plug, and the other end a male plug. Then buy a cheap LED torchlight. I bought a super bright one the other day at Sim Lim Tower for $18.00. The fibre optic cable that I have comes from my sound card bundle. Plug the female end of the cable onto the LED bulb. If they can't interface properly, use a tape or whatever to secure the connection. Switch on the LED torchlight and you will see a bright tiny light over at the male end. The light is less than 1mm across.....perfect for an artificial star! (actually the strand of fibre optic is smaller than that)
Because the source of light is so tiny, you don't need great distances for your star test. Suiter has a formula here to calculate the right distance, but with the fibre optic light, just bring it far enough for your scope to focus and you should have the right distance.
Try it and have fun star testing
How to make an artificial star the cheap and easy way
Vince, what will be the right distance according to suiter's formula if i use a multimode fiber (core is 62.5micron)? which simlim shop sells the superbright LED torchlight?However, I have found a cheap method in making a very tiny point of bright light that's good enough for testing your scope optics. What you can do is use fibre optic cables. Get a short length of fibre optic cables with one end a female plug, and the other end a male plug. Then buy a cheap LED torchlight. I bought a super bright one the other day at Sim Lim Tower for $18.00. The fibre optic cable that I have comes from my sound card bundle. Plug the female end of the cable onto the LED bulb. If they can't interface properly, use a tape or whatever to secure the connection. Switch on the LED torchlight and you will see a bright tiny light over at the male end. The light is less than 1mm across.....perfect for an artificial star! (actually the strand of fibre optic is smaller than that)
Because the source of light is so tiny, you don't need great distances for your star test. Suiter has a formula here to calculate the right distance, but with the fibre optic light, just bring it far enough for your scope to focus and you should have the right distance.
thanks,
arief
the right distance will depend on the size of the scope...ariefm71 wrote:Vince, what will be the right distance according to suiter's formula if i use a multimode fiber (core is 62.5micron)? which simlim shop sells the superbright LED torchlight?However, I have found a cheap method in making a very tiny point of bright light that's good enough for testing your scope optics. What you can do is use fibre optic cables. Get a short length of fibre optic cables with one end a female plug, and the other end a male plug. Then buy a cheap LED torchlight. I bought a super bright one the other day at Sim Lim Tower for $18.00. The fibre optic cable that I have comes from my sound card bundle. Plug the female end of the cable onto the LED bulb. If they can't interface properly, use a tape or whatever to secure the connection. Switch on the LED torchlight and you will see a bright tiny light over at the male end. The light is less than 1mm across.....perfect for an artificial star! (actually the strand of fibre optic is smaller than that)
Because the source of light is so tiny, you don't need great distances for your star test. Suiter has a formula here to calculate the right distance, but with the fibre optic light, just bring it far enough for your scope to focus and you should have the right distance.
thanks,
arief
If you are talking about an 8" scope...50-100 metres should be good enough.
The distance between the pinhole-based artificial star and scope, according to Suiter's recommendation, is 24 times the nominal focal length of the scope, which is 49m for my 8" f/10 sct.the right distance will depend on the size of the scope...
If you are talking about an 8" scope...50-100 metres should be good enough.
The diameter of pinhole for such distance, considering 0.56 arcseconds resolving power of my 203mm objective, should be 0.13mm. However, since I'm using a fiber optic strand with a very small diameter (0.0625mm), I only need the following distance to test my star:
d = D*206265/a = 0.0625*206265/(0.56*1000) = 23m !
Last edited by ariefm71 on Fri Jul 30, 2004 11:57 pm, edited 1 time in total.
Found a really good article off cloudy nights that talks about how to make a really really cheap artifial star. I figure that most people will have the materials lying around their houses, if not, buying the stuff they don't have shouldn't cost more than $10-20. Also has a handy reference to Suiters formula on distance per size of artificial star.
http://www.cloudynights.com/lab/technical/star.pdf
http://www.cloudynights.com/lab/technical/star.pdf