Making a "Fake Star" for Optics Testing

I am looking for suggestions on how to create a "Fake Star" that I can use
for indoor - daytime - optics testing. I have tried a laser pointer on a
wall but I cant seem to get the point to resolve to a clean "Star Like"
image in my scope.

I am sure this has been done - and I have even found one company that sells
such a device with little explanation as to its construction or use on the
site:
http://www.sunflower.com/%7Eclafever...ml/ezstar.html

It looks like some kind of a light box that fits over the end of a scope?

Any ideas on how to construct something that would be useful for testing
optics?

As always - thanks in advance!!

~derek

"Derek Overdahl" wrote in message
...
I am looking for suggestions on how to create a "Fake Star" that I can use
for indoor - daytime - optics testing. I have tried a laser pointer on a
wall but I cant seem to get the point to resolve to a clean "Star Like"
image in my scope.

I am sure this has been done - and I have even found one company that
sells
such a device with little explanation as to its construction or use on the
site:
http://www.sunflower.com/%7Eclafever...ml/ezstar.html

It looks like some kind of a light box that fits over the end of a scope?

Any ideas on how to construct something that would be useful for testing
optics?

As always - thanks in advance!!

~derek


Derek,

Try aiming your laser at a good sized ball bearing (or a silver Christmas
tree ornament?). You might find the ball bearings online as I see them all
the time at NEAF & Stellafane sold for this purpose although I believe they
are usually used outdoors with the sun as illumination...
Bruce

On Thu, 05 Aug 2004 00:48:51 GMT, "Derek Overdahl"
wrote:

I am looking for suggestions on how to create a "Fake Star" that I can use
for indoor - daytime - optics testing.

If you want to evaluate optical accuracy, the light from your source
needs to be firstly a point source, and secondly far enough away that
all light rays entering your scope are close as possible to parrallel.

This means that the light source should be as far away as possible, ie
over 100 metres depending on the aperture of the scope. If not , the
'star test' will show false spherical abberation.

"Derek Overdahl" wrote in message ...
I am looking for suggestions on how to create a "Fake Star" that I can use
for indoor - daytime - optics testing. I have tried a laser pointer on a
wall but I cant seem to get the point to resolve to a clean "Star Like"
image in my scope.

I am sure this has been done - and I have even found one company that sells
such a device with little explanation as to its construction or use on the
site:
http://www.sunflower.com/%7Eclafever...ml/ezstar.html

It looks like some kind of a light box that fits over the end of a scope?

Any ideas on how to construct something that would be useful for testing
optics?

As always - thanks in advance!!

~derek


The best thing is shining a light along the site line of the scope onto
a ball bearing. This gives you a non-resolvable disk as opposed to the
pin holes some use which are generally resolvable unless you have a
huge distance to space it from your scope. Also, remember to keep
the distance considerable (50' for a small scope) to avoid spherical
aberration effects of not being at infinity.
-Rich

Try a far away radio tower.

Derek;
I test optics all the time for a living. Here is what I use.

I get a 1/4" ball bearing from a bkie shop and use a 1/4" diam. source
of light at a distance of 1'. The perfect thing is one of the new
high intensity white LED key chain lights with a switch to keep it
on. They have them at outdoor stores.

You only need distance if you are evaluating optics. For collimation,
you can be as close as 30'. I use this set-up at 300 X to 400 X.

I hope this helps.

Steve D. White
TeleVue Optics N. American Rep.


www.televue.com

I have used one telescope looking directly into another. Any pinhole
light source viewed backwards through a telescope comes awfully close
to giving you an artificial star. Caveat - not everyone has two
scopes, and I would recommend that the scope you are using for
creating the light source be larger in aperature than the scope you
are collimating.

Gil