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How to Make an Astronomical Telescope

A simple telescope enlarges an image by flipping it on it's way to your eye. Extra lenses are needed to reflip the image so you see things right-side up. Since stars and planets have no "right side up" orientation, an astronomical telescope doesn't need the extra lenses and length required to right the image. The fewer lenses light passes through, the sharper and brighter the image. Isaac Newton's reflector telescope design takes advantage of this with a simple design that maximizes magnification while minimizing distortion and light loss.

Things You'll Need

Telescope primary mirror
Mirror cell commercial mount
Diagonal mirror mounted on spider the size of the sonotube
Focuser
Eyepiece to fit the focuser
Sonotube 2 inch greater in diameter than the mirror
Finder scope and mount

Instructions

Assembly
- 1
  Position the mirror on the mirror cell mount and gently tighten the mounting brackets. Do not adjust the collimating screws. Test fit the primary mirror assembly into the base end of the Sonotube so the bottom of the cell is even with the bottom of the tube. Measure the distance from the base of the mirror cell to the center of the surface of the mirror. Measure the same distance from the bottom end of the sonotube and mark the side. Remove the mirror while attaching other parts.
- 2
  Set the focuser on top of the sonotube at the upper end and measure the distance from the center of the Sonotube to the top of the focuser tube. Subtract this distance from the focal length of the mirror. The focal length is the distance from the mirror to the point where it focuses. This measurement can be found in the documentation for your mirror. Measure from the mirror mark you made at the bottom end of the Sonotube and mark the subtracted distance on the side of the tube. If the center to focuser distance is 7 inches and the focal length is 28 inches, then you will measure from the mirror mark 21 inches and mark the tube. This is where the secondary mirror will be positioned and the focuser will be attached. Cut the tube off about 4 inches above the focuser mark.
- 3
  Drill a hole in the Sonotube the diameter of the focuser tube at the spot where you made the upper mark. Set the focuser over the hole and screw it into place on the side of the tube.
- 4
  Mount the secondary mirror to the spider mount according to directions. Position the spider mount inside the upper end of the Sonotube so that the center of the secondary mirror is directly below the center of the focuser tube and screw the legs to the side of the Sonotube. Make sure the legs of the spider are exactly the same distance from the base of the tube so that the secondary mirror is lined up correctly with the center of the primary mirror.
- 5
  Screw the finder scope mount to the side of the Sonotube a quarter way around the tube from the focuser. The scope should be parallel to the main tube. It can be aligned by setting up the scope in the daytime and focusing on a distant object with the main scope. Adjust the finder scope so that the crosshairs are directly on the object in the eyepiece of the main scope.
- 6
  Slide the mirror cell assembly into the base of the telescope tube so the base of the mounting cell is flush with the base of the tube and screw into place. Collimate or align the mirror with the secondary. Look through the focuser tube. You will see an image of the secondary mirror reflected in the secondary from the primary. Adjust the collimator screws so that the image of the secondary is centered in the secondary mirror. Slip an eyepiece into the focuser tube end when ready to view the skies.
- 7
  Attach the telescope to a commercial mount or homemade Dobsonian mount according to the instructions that come with the mount.

Astronomy