Well, my suggestion of a small ornament works just fine. When I can use
1000 to 1500x and get good diffraction rings, the hole is small enough.
The ornaments curvature defines the "hole" as it is really the reflection
back to the scope from a -very- small area of the ornament.
Back a year ago or so, someone on one of the groups did some calculations
and came up with a 1.5 inch ornament was equivalent to a point source for
a 10 in scope. I dont remember the calcs, I could probably duplicate
them given some time but dont plan to. To me, the proof is that I can
collimate using my setup and the resulting collimation is better than I
can get with a star 95% of the time. Seeing being the reason the star is
not as good.
Trying to make a small hole round enough and small enough is a hassle.
You automatically get a round source from the ornament so you dont really
care about the size as it is symmetry that you are interested in. If the
hole is a "point" source, you get symmetry. However, the angular area of
the ornament also guarentees symmetry. The expensive "artificial stars"
are just not required.
Now, I am talking "collimation" here and not "star testing" a la Suiter.
There is a difference.
---------
Phil Chambers [ptchamb@No-Spam] (S.F. Bay Area - Calif. USA)
On Mon, 20 Jan 2003, Rob Hawley wrote:
> The concerns cited by Dennis were also echoed on the LX200GPS list. I am in
> no way recommending that vendor. I paid by credit card and am prepared to
> also stop payment if the device has not shipped. I am crossing my fingers
> that will not be necessary. I should note that I contacted the BBB serving
> Kansas and their report does not reflect the level of bad experiences I have
> heard on the newsgroups.
>
> The problem of creating a good star is harder then it seems. The light
> source for a 10" SCT needs to appear no larger than .45 arcseconds or the
> scope will resolve it as a non-point source. I leave to the reader to
> compute the tradeoff of distance vs hole size to get that value. I was quite
> surprised when I did the math. You need a very small round hole and a very
> bright light source. The advantage of the Eztelescope unit was they claim to
> have a very small hole.
>
> If you don't want to take the hassle (risk) with eztelescope.com you can try
> building it yourself. The light source you can get a radio shack (or
> elsewhere). The small hole is more of a problem (see the discussion on
> http://groups.yahoo.com/group/LX200GPS concerning the 25 micron orifices
> available through smallparts.com). That is certainly my plan B.
>
> Rob Hawley
>
>
>
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