Telescope Tear-DownAnatomy of a

114mm f/8

Newtonian Reflector

The Newtonian Telescope

Lock Adjust

The Mirror Cell

COLLIMATION

• Aligning the optical axis

• Centreing the light cone in the secondary mirror and eyepiece

The Optical Axis

• The direction the telescope is pointing

• All light from the focal point reflects parallel to optical axis

• Line from centre to focal point

• Axis intersects mirror at 90 degrees

• Focal point halfway between centre and mirror

• See reflection of eye where axis intersects mirror

Adjusting the Primary Mirror

• Still see reflection of eye where axis intersects mirror

• For parabolic mirrors the optical axis should intersect the mirror in the CENTRE.

• Align axis with tube to avoid tube blocking light.

Quick Primary CollimationThe view down the tube

• When reflection lines up with secondary we see the optical axis

• Adjust primary to centre optical axis

• Primary now roughly aligned with tube• Secondary reflection in centre of primary mirror• Reflection of camera lens (eye) in centre of mirror

Secondary Mirror Alignment

• Position mirror under centre of focuser tube

1 - Secondary mirror position

Secondary Mirror Alignment

• Centre reflection of primary

• Should see whole mirror - don’t cut off light!

2 - Aim the secondary mirror

Final Primary Collimation

• Reflection of eye is on the optical axis

• Move eye to centre of primary mirror

How close?

• Only eye reflection & centre matters

• F/8 => 11mm radius

• F/6 => 5 mm radius

• F/5 => 2.7mm radius

• Radius = Focal ratio3 x 0.022 mm