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How to Install a Curved Telescope Spider

A telescope spider holds the secondary mirror in place in Newtonian, Newtonian Dobson and Cassegrain reflector telescopes. Spider mounts with curved arms are often used in reflector telescopes as they reduce the effect of diffraction on the image reaching the eyepiece. Curved spider mounts have one to four arms. Two have the least effect on image quality while three and four are easiest to mount for amateur astronomers.

Things You'll Need

Telescope spider
Cardboard
Pencil
Protractor
Ruler
Electric drill
Drill bits
Mounting screws
Screwdriver
Matte black paint
Brush

Instructions

Calculate Offsets
- 1
  Adjust the threaded bolt running through the spider vane connected to the diagonal mirror so there is about three-quarter's of an inch between the spider vane mount and the back of the diagonal mounting.
- 2
  Measure the distance V from the center of the spider vane, where the vane will be attached to the tube, to the center of the diagonal mirror. Include roughly one-half inch for fine adjustment between the spider vane and the diagonal mount.
- 3
  Measure the distance T from the end of the tube to the center of the eyepiece hole.
- 4
  Calculate D, subtracting V from T. D will be the distance from the end of the tube to the concentric circle inside the tube where holes to mount the vane will be drilled.
Drill Spider Vane Holes
- 5
  Make a circular cardboard template the same diameter as the inside of the telescope tube.
- 6
  Mark the center of the template and draw a line through it from one side to the other -- one diameter.
- 7
  Use a protractor to measure the angle to each hole -- ninety degrees each for four-vane spiders, one-hundred and twenty degrees for three-vane spiders and one-hundred and eighty degrees for a two-vane spider.
- 8
  Mark the edge of the template for each angle arc.
- 9
  Place the template in the top edge of the tube.
- 10
  Mark the edges of the tube where each radius for each arc hits the circumference of the template.
- 11
  Mark the distance D from the edge of the tube where you have marked the tube at right angles toward the other end of the tube for each hole.
- 12
  Measure the diameter of the holes in the spider vane. Pick a drill bit slightly smaller than these holes. Drill the holes in the tube. Make sure to clean the holes after they are drilled.
Mount the Spider
- 13
  Put the spider into the telescope tube.
- 14
  Align the holes in the end of the spider vanes with the holes in the tube.
- 15
  Attach the spider with screws or screws and bolts between the spider and the tube.
- 16
  Dry brush black matte paint on any bolts on the vane that may not be matte black to ensure no extra light interferes with the image.
- 17
  Attach the secondary mirror to the spider and adjust with the bolt between the vane and secondary until it is centered in the eyepiece hole.

Astronomy