Artificial Star

C.C.: LX90 Yahoo group.
I remember someone posting a link to their site. I don't remember if
the post was here or in S.A.A. so I'll also post to SAA in hopes of finding
him.

The main page had a "projects" link to another page, on that page was a
list of projects which one of them was an Artificial Star. That showed
Radio Shack equipment and the math for hole diameter and distance. I'm
building one of these and would like a refresher course specifically from
that site. Was it someone here and could you post the link?


--
Michael A. Barlow

Found!
http://users.bigpond.com/lansma/projects.htm
Thanks anyhow,
--
Michael A. Barlow

"Michael Barlow" wrote in message
...
C.C.: LX90 Yahoo group.
I remember someone posting a link to their site. I don't remember if
the post was here or in S.A.A. so I'll also post to SAA in hopes of
finding
him.

The main page had a "projects" link to another page, on that page was
a
list of projects which one of them was an Artificial Star. That showed
Radio Shack equipment and the math for hole diameter and distance. I'm
building one of these and would like a refresher course specifically from
that site. Was it someone here and could you post the link?


--
Michael A. Barlow

On Sun, 31 Oct 2004 12:53:03 GMT, "Michael Barlow"
wrote:

C.C.: LX90 Yahoo group.
I remember someone posting a link to their site. I don't remember if
the post was here or in S.A.A. so I'll also post to SAA in hopes of finding
him.

The main page had a "projects" link to another page, on that page was a
list of projects which one of them was an Artificial Star. That showed
Radio Shack equipment and the math for hole diameter and distance. I'm
building one of these and would like a refresher course specifically from
that site. Was it someone here and could you post the link?

The best artificial star is a small ball bearing.
Mount a 1/4" ball bearing on a black card or piece of
wood. When testing the scope, point a flashlight (attach
it to the top of a camera tripod) at the ball bearing.
The flashlight can be right next to the telescope.
Making artificial stars by punching holes in metal or
cardboard is a waste of time. Usually, they are not round,
they have flaws that show up in the star test unless you
are far enough away from them so that they are not
resolvable. With a scope of any size, this means a large
distance, increasing the chance that localized heat waves
will interfere with the testing.

The best artificial star is a small ball bearing.
Mount a 1/4" ball bearing on a b

I folded a piece of aluminium foil about 8 to 16 times. I then put a small
sewing needle in a drill press and came down on the folds untill it just
punctured the fold. Then I looked for the smallest hole I could find with a
10x loop. Eventually I put one of pieces in an enlarger and made a print and
enlarged the h--- out of it. Suprisingly it was quite round.

On 31 Oct 2004 21:32:59 GMT, (HAVRILIAK) wrote:

The best artificial star is a small ball bearing.
Mount a 1/4" ball bearing on a b

I folded a piece of aluminium foil about 8 to 16 times. I then put a small
sewing needle in a drill press and came down on the folds untill it just
punctured the fold. Then I looked for the smallest hole I could find with a
10x loop. Eventually I put one of pieces in an enlarger and made a print and
enlarged the h--- out of it. Suprisingly it was quite round.

Another problem; The smallest hole is not the one you are looking
for. You are looking for the largest hole possible that cannot be
resolved. Reason? You have to provide illumination for the star
and a larger hole provides more, unless the illumination source
is smaller than the pin hole which is very unlikely.
-Rich

RichA wrote in message . ..
On Sun, 31 Oct 2004 12:53:03 GMT, "Michael Barlow"
wrote:
snip The best artificial star is a small ball bearing.
Mount a 1/4" ball bearing on a black card or piece of
wood.

The ball bearing or Christmas tree decoration tricks are the preferred
inexpensive methods - and the one I use personally. If needed for
indoor bench work, at significantly greater expense, commercial
pinhole aperatures are available through Edmund:

http://www.edmundoptics.com/onlineca...productID=1794

- Canopus

I bought a Picostar

http://www.digitalastronomy.com/html...mation_aid.asp

It works perfectly with adjustable magnitudes from 1 to 8 and only needs to
be 20 metres from my 6" scope which just fits into my yard.

I was a bit sceptical at first but it works as advertised and I'm really
happy with it.

--

Regards,

Eddie Trimarchi
~~~~~~~~~~~
http://www.astroshed.com
http://www.fitsplug.com

"Michael Barlow" wrote in message
...
C.C.: LX90 Yahoo group.
I remember someone posting a link to their site. I don't remember if
the post was here or in S.A.A. so I'll also post to SAA in hopes of
finding
him.

The main page had a "projects" link to another page, on that page was
a
list of projects which one of them was an Artificial Star. That showed
Radio Shack equipment and the math for hole diameter and distance. I'm
building one of these and would like a refresher course specifically from
that site. Was it someone here and could you post the link?


--
Michael A. Barlow

On Mon, 01 Nov 2004 03:31:14 GMT, "Eddie Trimarchi"
wrote:

I bought a Picostar

http://www.digitalastronomy.com/html...mation_aid.asp

It works perfectly with adjustable magnitudes from 1 to 8 and only needs to
be 20 metres from my 6" scope which just fits into my yard.

I was a bit sceptical at first but it works as advertised and I'm really
happy with it.

I'd suggest anyone interested in star testing read "Star Testing
Astronomical Telescopes" from pg. 80 onward.

I'd suggest anyone interested in star testing read "Star Testing
Astronomical Telescopes" from pg. 80 onward.

Yes it's a great book, I've had it since it was first published.

But I really only bought the Picostar for daylight collimation.
--

Regards,

Eddie Trimarchi
~~~~~~~~~~~
http://www.astroshed.com
http://www.fitsplug.com

"RichA" wrote in message
...
On Mon, 01 Nov 2004 03:31:14 GMT, "Eddie Trimarchi"
wrote:

I bought a Picostar

http://www.digitalastronomy.com/html...mation_aid.asp

It works perfectly with adjustable magnitudes from 1 to 8 and only needs
to
be 20 metres from my 6" scope which just fits into my yard.

I was a bit sceptical at first but it works as advertised and I'm really
happy with it.

I'd suggest anyone interested in star testing read "Star Testing
Astronomical Telescopes" from pg. 80 onward.

"Michael Barlow" wrote in message . ..
Found!
http://users.bigpond.com/lansma/projects.htm

If the star is only for collimation purposes, matching scope's
resolution is not necessary. But if it is intended for testing
correction error, the thing to begin with is to determine max
tolerable amount of error induced to a particular system due to the
star being relatively close. Even as little as 0.1 wave s.a. induced
can significantly change test result. For instance, system with
inherent 0.25 wave overcorrection and 0.1 wave induced undercorrection
will test 0.15 wave overcorrected, while system with 0.25 wave
inherent undercorrection would show 0.35 wave undercorrection. For
reliable test results, the induced error shouldn't be greater than
~0.05 wave.

Needed star distance for any given amount of induced error depends on
the aperture, F# and design. For parabolic mirror, the induced error
is reduced to ~0.05 wave (overcorrection) at 150(D/F)^2 feet, for D in
inches (the error here increses nearly in proportion to decreasing the
distance).

For doublet achromat, induced error diminishes to ~0.05 wave
undercorrection at 18D^2/F feet, and for the commercial f/10 SCT at
5D^2 feet (likely to have a mixed bag of over- and undercorrection for
different zones). These figures are approximate, because they vary
somewhat with particular system parameters, but do give a good general
idea.

For even medium size apertures these distances are large enough that
super small openings are not necessary. Optimum size for an 8" f/10
SCT would be ~0.2mm.

Vlad