Hubble 5-star Artificial Stars
To most accurately test and collimate telescopes, reflectors, catadioptric, and
refractors, you must perform a star test. However, to do so, you need a star. Sadly, a real
star is not always available due to poor weather conditions or location. Even when a star is
available, you will need a good tracking system for doing star test as the star is always
moving. Also air turbulence may affect your test, and the real star may not even reveal the
true quality of your telescopes or give you a perfect collimation.
An artificial star is an excellent alternative to the real star. With an artificial star, star tests
can be accurately conducted anytime and anywhere. However, the problem with the
artificial star is that you need many different sizes of artificial stars for different telescopes
of different apertures with different focal ratios, and even for the same telescopes but at
different distances, and under different lighting environments.
The innovative Hubble 5-star Artificial Stars is the perfect solution to the star test problem. It
has 5 bright white LEDs with 5 precision pinholes (50/100/150/200/250 microns). The
Hubble 5-star Artificial Stars enables you to test virtually all telescopes, regardless of
aperture size, focal ratios, distance, and lighting conditions.
- You can instantly find out which star is best for your particular telescope at any
particular distance and lighting environment by simply choosing the smallest
possible star that still gives you a clear and defocused image.
- You can even adjust the brightness of the stars by twisting the LED cap.
- You can mask out any 4 of the 5 stars with a provided magnetic mask.
With Hubble 5-star Artificial Stars, telescopes are now easy to test and collimate!
Special Introduction offers:
The single unit: $24.95 ($19.95 +$5 Shipped Worldwide)
(regular price $29.95)
The 2 unit pack: $46.40 (Shipped Worldwide)
(regular price $55.50)
Shipped via HKPS airmail from Hong Kong,
6-10 business days delivery
Copyright 2009, All Rights Reserved
Q1: Is there a printed document for the Hubble 5-star Artificial Star(s)?
There is no printed document. But we will maintain this online FAQ up to date as a brief
document to the 5-star. Here is the printable version of this FAQ.
For complete and detailed instruction on the collimation and star test, please refer the
must have book by Harold Richard Suiter, Star Testing Astronomical Telescopes, Second
Q2: Where do you place the 5-star during the test?
The 5-star can just sit on a tripod top, on a table, or even on a rock. You need to aim the
star roughly towards (no precision aiming required!) to your telescope; then aim your
telescope to the 5-star. The 5-star provides a very wide angle for a very easy usage.
Q3: Which of the 5 stars do I use for the star test?
Choose the smallest possible star that still gives you a clear defocused image. You may
need to dim the stars with the new batteries by twisting the LED head cap. You change the
brightness by adjusting the alignment among the LEDs and the pinholes. Change
batteries if all stars are too dim to see clearly.
Q4: How far should the 5-star be placed from the telescope?
The 5-star should be placed at a distance from the telescope about M times of the focal
length of FL; M is 336*D/F^3, or 336*D/(F*F*F) for a Newtonian(May, 1991, Sky and
Telescope, Roger Sinnott), where D is the Clear Aperture (in inches) and the F is the focal
ratio. E.g., if your scope is 10" F/5, then the M is 336 x 10 / 5^3 = 336 x 10 /(5 x 5 x 5) =26.88.
So the 5-star need to be M x FL = M x D x F = 26.88 x 10 x 5 = 1344" away, or about 34 m
away. In general, a minimum of 20 for the M is suggested by Suiter.
The above distance is for the real star test, for the collimation purpose; about 70% of
above distance is good enough.
As long as you have enough back focus to focus on the close by object, you will be
surprised how close you can get for the collimation. You may need to add one or two
focuser extension tubes.
Q5: How do I perform the collimation with the 5-star?
First you should check if the scope is in rough collimation by observing a strongly
defocused star image (about 10 wavelets, or move focuser in or out until seeing about 5-
10 rings). All rings and shadows should be concentric; if not, please perform the
collimation according to the instruction of the telescope until all rings and shadows are
concentric. You should do this at a magnification of 25X of your scope’s diameter (in
Coma due to misalignment of a 10" F/8 scope:
Then you need to do a fine and final collimation by observing the focused 50 microns
star image, the famous Airy disk with a magnification of at least 50X of your scope’s
diameter (in inches). Use a 2X, or 3X Barlow lens if necessary. You should see a
uniform, complete, and concentric Airy disk and diffraction rings if the scope is in
perfect collimation. Follow the same procedure to do minor adjustment on your scope
until you reach a perfect collimation.
This is most accurate method to collimate your telescope. In a real star the seeing
limit make it unlikely for you to see the Airy disk or to achieve this level of
Some excellent review articles on 5-star:
An Astromart Article by Greg Nowell
A Cloudy Nights Review Article by Bill Faatz
A Cloudy Nights Review Article by Steve Bennetsen
An Astronomy Technology Today Review Article by David Snay
The Easy Way to Align Your Telescope's Optics: Indoor Artificial Star Collimation
by Derek Wallentinsen
Some feedbacks from our customers:
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happy. Clear skies to you and may your summer days be warm and full of sales!
-Works a treat! Great Astro bargain. Highly recommended. Very Fast delivery!!!
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-This little thing is fabulous value for the few dollars you are charging. I've been
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Extremely good value at the price you are selling it for.
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-The best $20 astronomical investment I have ever made.
-My SCT was collimated better than it's ever been that night, and, I did the
collimation in broad daylight.
-Wow, it really works, even at 86 ft. I just have to keep direct sunlight off the
artificial star so there's enough contrast to see the "airy disc" and you're good
to go. I can't wait to see it against the stars tonight, my scope was pretty
decently (and quite noticeably) out of collimation. Now I feel it's pretty darn spot
-I first made sure the focuser was properly aligned. I then used a barlow laser to
make sure both secondary and primary were aligned. Then using the artificial
star, I tweaked the primary. I had to move two knobs each about 1/8th of a turn at
most. I then locked the mirror with the locking screws, and pointed up at Polaris.
It was pretty darn spot on…
I measured the holes of both (units) using a scanning electron microscope at
work... The microscope can reliably measure down to less than 10 nanometers
(0.01 micrometers). Considering a single 50 micron laser drilled hole in stainless
steel disc (unmounted and no LEDs) can run $40-50 from commercial suppliers
here in the US, this is a fantastic bargain! Thanks very much.
-Your 5-Star Artificial Star is GREAT! I've never had an easier time collimating my
SCT. Thanks for a great product.
Great product, good price! I wish I had bought this sooner!!
I am wondering why I didn't get one of these long ago...
-My dad is very pleased with his birthday gift. Thanks.
-Great Little item! Collimation's a snap with this tool.
Simply put ,you exceeded by far my biggest hopes.
-Very, very, very great tool. Should have had it years ago. Excellent a+
It's the best astro tool that I ever bought... In my opinion, it looked much better
than a real star.
Every telescope user should have one.
Q6: How do I perform the star test with the 5-star?
Choose an appropriate star for your scope (Q2). After making sure the scope is in
perfect collimation(Q4), follow the normal Star Test procedure to perform the test.
Q7 After inserting the batteries, why isn't the unit turned on?
Please make sure all cells are inserted in right direction, the spring to the negative.
Please re-insert all the cells if necessary to make sure all cells are contacting the
nodes. Try some new cells in necessary.
Q8: How was the Hubble Space Telescope tested after it had been launched into the
The star test was used extensively and exclusively for the diagnosis and verification for
the Hubble Space Telescope in the space.
Referring to the last image attached (The imaging performance of the Hubble Space
Telescope, by C.J. Burrows et al, Astrophysical Journal, March, 1991), "The left two
columns (note that the first and third columns in the first two rows are not clear enough
to be visible) show observed images of bright stars at two different scales, while the
right columns show correspond models. The top two rows show images taken on each
side of the nominal focus position. These images clearly demonstrate the presence of
spherical aberration. Instead of a uniformly illuminated pupil image, the inner or outer
edges are brighter"
Here is a description (F. Roddier, C.Roddier, Appl. Opt. 32, 1993) on how the star
test was conducted on the Hubble Space Telescope (HST) , “we requested that the
highly defocused images be taken in flight by HST so that the method (the Roddier
method) could be applied to estimate the exact amount of spherical aberration.
Because defocusing the imaging also defocus the telescope tracking system, it
was not possible to obtain images sufficiently defocused for the method to apply.
However, defocused images recorded by the HST are not blurred by the
atmosphere and can be taken through narrow-band filter. In this case the wave-front
information is still preserved and can be recovered by using phase-retrieval
The following Star test images are from, Phase-retrieval analysis of pre- and
post-repair Hubble Space Telescope images, John E. Krist and Christopher J.
Burrows, 1 August 1995, APPLIED OPTICS