Collimation:

1) Roughly checking: Take eyepiece off, look into eyepiece holder. The diagonal (or secondary mirror) should be centered. The reflection image of primary mirror should be centered. The image of your eye should be centered. To do this 'Sight Tube' is useful collimation tool to ensure all are centered. If things are not centered, goto next step

2) Start collimation: insert sight tube into eyepiece holder (picture shown Orion collimating eyepiece which is hybrid between sight tube and Cheshire eyepiece) adjust insertion depth to ensure clearly see outer edge of diagonal when look through the sight hole. Lock it by tighten the thumbscrew. Point telescope to day sky away from sun and look through the site hole. Sight tube can be used only on day time but Cheshire eyepiece can be used on night time by using external light source e.g. flash light. The collimating eyepiece manual can be down load at Orion Customer Support section. The instruction can also be applied for sight tube as well. Please see D.I.Y section.

3) Adjust diagonal if diagonal is not centered. Adjust central bolt in and out until the diagonal mirror is centered in view. It may needs to release three pivot bolts while do this. Turn pivot bolts until the reflection of the primary is centered. I made a center spot on primary mirror for centering guide. The center spot have no diverse effect due to it hide under diagonal shadow.
At first time I can't center the diagonal as central bolt seem to be too short. Then I removed a rubber pad (3mm thick) and gain sufficient adjusting distance.

4) Adjust the primary: loosen three lock bolts (the long ones) adjust three short bolts until the eye image (the reflection of sight hole or reflection of bright annulus of Cheshire eyepiece) is centered. The supplied lock bolts were too short, then I changed with the longer ones, according to the offset distance form base ring & mirror cell support is quite high.

refer to Orion
Left: After centering diagonal. The diagonal is centered under focusing tube but the reflection of primary and the reflection of sight hole are off centered.
Center: After completed diagonal tilting adjustment (by 3 pivot bolts) the center spot of primary is centered at cross hair. But the reflection of sight hole is still off centered.
Right: When completed primary alignment, the reflection of sight hole is centered.
Mel Bartel collimation page gives an excellent overview & procedure for newtonian reflector.

star test
Star test is very accurate testing method should be done after completion collimation above.
The briefly procedure : (1) point telescope to bright star (2) slowly rack the image out of focus, if the Image is unsymmetrical, the scope is out of collimation.
The quick collimation (from Sky & Telescope, Jun 2001, page 125): (1) Move the image around FOV by adjusting RA/DEC control knob until receive symmetrical image (2) Adjust primary to move the image to be centered. Repeat whit higher magnification eyepieces for more accuracy.
For more information on star testing, Thierry Legault is precise/concise web page and gives viable procedures. The cassini division of Saturn should be seen with collimated telescopes.
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