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How to Test a Telescope Mirror

Most experienced amateur astronomers will tell you that it is a uniquely rewarding experience to craft your own telescope. This generally involves grinding a mirror into a parabolic shape that will accurately reflect the night sky. Once you feel you have gotten the mirror's dimensions right, it is important to test for accuracy. Several test are available to help you in your quest to see the night skies in all its extraordinary wonder, but most backyard astronomers use a simplified Ronchi test to check their mirror's calibration.

Things You'll Need

Telescope mirror
Light bulb
Thin lined paper, stripes 2-3 mm apart
Small cardboard box
Box cutter
Freestanding light socket

Instructions

- 1
  Take your light socket and place it against the center of the outside of the small cardboard box. Using a marker, trace around it so you have a precise hole in which to place the socket. Make sure it is placed where the light bulb will not touch any of the sides.
- 2
  Cut a hole with your box cutter where you have drawn the circle, be careful to not stray too far outside of the line lest your hole be too big to hold the socket firmly. On the opposite side of the box, cut a 1 inch by 1/4 inch slit, lengthwise.
- 3
  Place the socket in the hole and screw in the light bulb. Test the bulb by plugging the socket in, unplug, and set aside.
- 4
  Using a darkened workspace, position your mirror where it can take a beam of light from the light source. Place the lined paper in between your mirror and your light source. Check the image in the mirror. If the image of the lines is distorted, then your mirror may need some fine tuning. If they are perfectly straight, then your mirror is in good shape.

Astronomy