Telescope Tear-Down Anatomy of a 114mm f/8 Newtonian Reflector.
Transcript of Telescope Tear-Down Anatomy of a 114mm f/8 Newtonian Reflector.
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Telescope Tear-DownAnatomy of a
114mm f/8
Newtonian Reflector
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The Newtonian Telescope
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Lock Adjust
The Mirror Cell
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COLLIMATION
• Aligning the optical axis
• Centreing the light cone in the secondary mirror and eyepiece
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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
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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.
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Quick Primary CollimationThe view down the tube
• When reflection lines up with secondary we see the optical axis
• Adjust primary to centre optical axis
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• Primary now roughly aligned with tube• Secondary reflection in centre of primary mirror• Reflection of camera lens (eye) in centre of mirror
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Secondary Mirror Alignment
• Position mirror under centre of focuser tube
1 - Secondary mirror position
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Secondary Mirror Alignment
• Centre reflection of primary
• Should see whole mirror - don’t cut off light!
2 - Aim the secondary mirror
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Final Primary Collimation
• Reflection of eye is on the optical axis
• Move eye to centre of primary mirror
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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