Here’s a basic guide that’s good enough for visual use ……
Collimating a Newtonian Reflector Telescope
Tools needed
Cheshire collimating 1.25mm eye piece
Laser collimator eg: Orion LaserMate Mk 2
Allen key or Phillips head screwdriver
Collimation is the process of aligning the telescope optics ( secondary mirror and primary mirror ) to the central point of the telescopes focuser. Light enters the telescope opening , reflects off the rear primary mirror to the front secondary mirror and then directed up the focuser tube to an eye piece or camera sensor.
It is important to accurately align the optical system in a Newtonian Reflector telescope to ensure the reflected image ( eg: Star ) is precise and not distorted in any way once it is focused. Both Secondary mirror and Primary mirror have 3 adjustment screws for 3 points of adjustment.
Secondary mirror can be adjusted for tilt, rotation and longitudinal adjustment
Primary mirror can be adjusted for tilt in 3 planes.
The Secondary mirror is adjusted first followed by the Primary mirror last.
Step 1 - Remove all lids and covers from telescope. Place the laser collimator fully home into the focuser with its bulls eye target cut away section facing square to the rear end of the telescope or towards the big Primary mirror and tighten up focuser grub screws. Switch on laser collimator.
Step 2 - Adjust the small Secondary Mirror using the 3 secondary mirror or front adjustment screws ( normally Phillips head ) on the front of the telescope until the red laser dot is precisely in the centre of the big Primary Mirror’s tiny white donut central target. This takes some practice to get it centered. Once centered leave the laser collimator switched on.
Step 3 - Now go to the rear of the telescope and look along the telescope to the focuser and the laser bullseye target of the laser collimator.
Ideally you do not want to see a laser red dot in the collimators bullseye target, instead you want to see just a faint even red glow of the laser around the bullseye target central small black hole. To adjust , loosen the 3 Primary mirror locking knobs ( anticlockwise a few turns ) and then adjust the other 3 Primary mirror collimation adjustment knobs to achieve an even red laser glow around the central bullseye target and small central black hole.Once adjusted as best as possible, carefully and lightly tighten up ( just a bit ) the 3 Primary mirror locking knobs. You may have to check the even red laser glow again as it may have moved slightly as a result of tightening up the 3 locking screws. This also takes some practice.
Step 4 - Go to the front of the telescope again and check to make sure the Secondary Mirror collimation adjustment still has the laser dot centered precisely in the centre of the big Primary mirror’s tiny white donut marker.
Step 5 - Once satisfied both Secondary and Primary mirrors are collimated correctly, switch off the laser and remove from focuser. Your telescope is now Collimated ready for use.
NB: You can also use a Cheshire 1.25mm collimation eye piece in the focuser to double check the laser collimation adjustments.
This site is also very popular for first time owners of Newtonians …..,
https://www.astro-baby.com/astrobaby...ian-reflector/
Cheers
Martin