From: Dale Eason 
To: "Jerry B. Hillman" , atm{at}shore.net
Reply-To: Dale Eason 


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In his book "Star Testing Astronomical Telescopes" by Harold
Richard Suiter Chapter 5.2 Artificial Sources he gives a table of
Reflective Sphere diameters that can be used.  For a 16" F5 a 3.0 inch
diameter sphere or smaller (a silver glass Christmas ornament) will work
well.  He also gives a distance table on page 85.   For the same mirror you
want place the sphere about 47 times the
Focal length away from the scope.  He also gives information on how to
calculate the tables.

You will want the background to be as dark as possible.

As a footnote he writes: "I do not recommend the star test as the sole
method of testing during fabrication.  It is best used as an independent
check of workshop tests.  The star test can be quite confusing when two or
more types of surface deformation are contributing to the errors."

"Jerry B. Hillman"  wrote:

Hi all,
Is it feasible to use the reflected image of the sun off of a ball bearing
to do daytime star testing?
My property is large enough that I can place the ball bearing up to 650
feet away. If so, would a 1/4" ball bearing be big enough? If I could
do this then it would give me many more opportunities to star test. (It is
cloudy today or I would already be trying it.) Clear skies, Jerry




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In his book "Star Testing Astronomical Telescopes" by
Harold Richard
Suiter
Chapter 5.2 Artificial Sources he gives a table of Reflective Sphere
diameters that can be used.  For a 16" F5 a 3.0 inch diameter
sphere or smaller (a silver glass Christmas ornament) will work
well.  He also gives a distance table on page
85.   For the same mirror you want place the sphere about
47 times the Focal length away from the scope.  He also gives
information on how to calculate the tables.
 
You will want the background to be as dark as possible.
 
As a footnote he writes: "I do not recommend the star test
as the sole
method of testing during fabrication.  It is best used as an
independent check of workshop tests.  The star test can be quite
confusing when two or more types of surface deformation are contributing to
the errors.""Jerry B.
Hillman" <JBHillman{at}ev1.net>
wrote:

Hi all,Is it feasible
to use the reflected image of the sun off of a ball bearingto do
daytime star testing?My property is large enough that I can place
the ball bearing up to 650 feetaway. If so, would a 1/4"
ball bearing be big enough? If I could do thisthen it would give
me many more opportunities to star test. (It is cloudytoday or I
would already be trying it.)Clear skies,
Jerry
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