Hubble 5-star Artificial Star(s)

Q1: Where do you place the 5-star?
The 5-star can just sit on a tripod top, on a table, or even on a rock; you only need to aim the star roughly towards (no precision aiming needed) to your telescope; then aim your telescope to the 5-star. The 5-star provides a very wide angle for a very easy usage.

Q2: How far should the 5-star be placed from the telescope?
For a Newtonian, the 5-star should be placed in distance to you scope about M times of the focal length. M is 336*D/F^3 (May, 1991, Sky and Telescope, Roger Sinnott), where D is the diameter of the mirror (in inches) and the F is the focal ratio. I.e., if your scope is 10" F/5, then the M is 336*10/5^3 = 26.88. So the 5-star need to be M * (D * F) = 26.88 * 10 * 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 should be more than enough.

Q3: Which of the 5 stars to use for the star test?
Choose the smallest possible star, but which still give you clear defocused image. You may need to dim the stars with the new batteries by twisting the LED head cap. Basically you change the brightness by adjusting the alignment among the LEDs and the pinholes. You need to change batteries if all stars are too dim to see clearly.

In theory, the diameter of the pinhole should not be larger than the M * Airy disk = M * 1.22 * l * f /D (where M is the distance factor (see Q2), l is the wavelength, D is the aperture diameter, and f is the focal length)

Q4: How to 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 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 inches).

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 50X of your scope's diameter (in inches). Use a 2X, or 3X Barlow lens if necessary;You should see an uniformed, 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 the final judgment of the collimation of your telescopes and all other collimation tools and methods! Due to the seeing limit, you will most likely not be able to see the Airy disk with a real star!

Q5: How to 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.

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