Folded Newtonian Optical Layout

The 6″ flat obstructs 37% of the diameter and 14% of the area of the primary

2″ diagonal – only optical component that was purchased


The problem with spherical mirrors

  • Spherical Mirror
    Diameter = 16″ (400 mm)
    Focal Length = 10′ (120″, 3000mm)
    f/7.5
    Thickness = 1.5″
  • Assume Entrance Pupil = 400mm
    Minimum magnification = 7 mm exit pupil
    57x
    Requires eyepiece = 53mm fl ~ 1degree FOV of sky
  • Maximum magnification
    2mm exit Pupil
    200x
    Requires eyepiece = 20mm fl ~ one quarter degree of sky
  • Eyepiece Built: 2″ diameter
    44mm Focal length – super Plossl design
    Gives 70x mag and 5.7mm exit pupil
    field of view = span of the double cluster

Primary is spherical? What about aberration and coma? What to do:

  1. Ignore it?
  2. Refigure to a parabola? Maybe not.
  3. Correct optically? Use thick positive lens at image plane (Simple PVC)
  4. Deform the mirror to form a sphere into a parabola (pull down center)

We tried # 4 first!


The flexing mirror cell