Transcript Telescope Tear-Down

Telescope Tear-Down
Anatomy of a
114mm f/8
Newtonian Reflector
The Newtonian Telescope
The Mirror Cell
Lock
Adjust
COLLIMATION
• Aligning the optical axis
• Centreing the light cone in the secondary
mirror and eyepiece
The Optical Axis
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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 Collimation
The 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
1 - Secondary mirror position
• Position mirror under centre of focuser tube
Secondary Mirror Alignment
2 - Aim the secondary mirror
• Centre reflection of primary
• Should see whole mirror - don’t cut off light!
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