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• If the seeing is steady and you have found and are tracking a moderately bright
star, very close to the center of the eyepiece at medium low magnification then
you are ready to slightly defocus the star image.
What you should see is a diffraction pattern or rings around rings around rings. This
pattern of rings should (if you are in perfect collimation) be concentric, or forming a
perfect "doughnut" like shape. You should have a fuzzy edged doughnut forming a
perfect circle of rings inside of rings inside of rings. These rings can be faint, and if the
seeing conditions are poor or the atmosphere to turbulent (not steady skies like described
above) you may not be able to see them at all.
Perhaps you will see these rings, but the perfect concentric doughnut I described above
will look more like an Egg with a hole in it! Not to worry, this is what we were looking
for and is by far the most likely cause of any slight loss in image sharpness, contrast or
less than stellar telescope performance.
If you have an Egg, not a Doughnut then you will want to move the defocused image
slightly off center in the direction of the hole. Do this so when you make your
adjustments, the image will be moving back towards the center of the field of view.
• Once you have off centered the image in the direction of the hole, you are now
ready to adjust the SMALLER screws on the back of the telescope.
• Use the smaller Allen key adjustments closest to the outside of the telescope as
you are looking at the back.
• You are now ready to make the elliptical egg into a perfectly concentric doughnut.
• Please note there are adjustment screws closer "In" towards the focuser (these are
for collimating the focuser do not use these for this Star Test adjustments)
Once you have made your defocused star a concentric ring of diffraction rings, you can
replace the Low/Medium powered eyepiece with a higher magnification eyepiece.
Repeat the process until you have achieved your best collimation.
If you can not achieve collimation the above way, then either the Primary Mirror,
Secondary Mirror or, as unlikely but not impossible, the Focuser may be
mechanically off. If so, then it is easiest to check the Primary Mirror first. If it is true,
then move to the Secondary Mirror check and finally to the Focuser.
Primary Mirror
•
Find an evenly illuminated wall greater than 20 feet away that you can point the
telescope towards.
• Remove everything from the focuser drawtube at the back of the telescope and
focus so the tube is completely inside the telescope.
• Put your eye approximately 2" from the edge of the focuser and look straight
down the inside edge of the focus tube (do not center your eye down the focus
tube, your eye is looking down the focuser on the inside edge).
• Look at the Outer Edge of the CENTRAL BLACK DOUGHNUT as your eye is
along the edge of the focuser.
Vixen Optics a Division of MrStarGuy, Inc. Copyright 2006
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