I live in a neighborhood with a lot of light pollution so I've made a light shield that blocks a lot of neighborhood light. In addition, the light shield can be disassembled to pack flat when transported.
Why use a light shield?
A light shield reduces observing fatigue because both eyes are open during observing. Without a light shield the observer may close one eye while keeping the other eye open which results in fatigue. This is particularly beneficial in light polluted areas, but is also beneficial under dark skies.
A light shield can increase the limiting magnitude, allowing the observer to view fainter objects because there is less distraction from ambient light.
The light shield is effective in blocking light from the side. However, it does not block light from directly behind the observer. A (photographer's) hood could be used in combination with the light shield to block light from directly behind the observer.
I have included the dimensions for my light shield.
DISCLAIMER: I arrived at this design after many iterations. Dimensions in my design should be used AS A GUIDE only. You will have to modify this design to work with your focuser. Here are links to my design:
The light shield also acts as a dew shield for the eyepiece. The lower part of the light shield is cut out to allow air circulation and to prevent your breath from fogging the eyepiece on cool nights.
I bought black plastic from Tap Plastics in Portland, Oregon.
Here are some photos of the light shield:
Note that there is a piece of black cloth stapled to the bottom edge of the plastic
to prevent light from "leaking" into the shield.
All the 1/4" holes are either punched with a hole punch or drilled with a 1/4" drill bit.
I placed the plastic between two pieces of thin plywood to drill the holes.
This photo shows one of two tabs that hold the light shield together.
The light shield mounts on the outside diameter of the focuser.
You must have a snug fit between the light shield and the outside
diameter of your focuser for this design to work.
The tabs are stapled in place using a paper stapler.
Note that the focuser hole is a little to the right of center because my right eye is my stronger eye.
You can put the focuser hole in the center or toward the left if you choose.
This is how my focuser appears without the light shield installed.
Note that I've added a dew shield to the TelRad finder scope.
Some of my astronomy projects:
12.5" F4.5 String Telescope
Two Cylinder Equatorial Platform with Floating South Mount
Flex Ring (Flexible upper ring used with four strut string telescope)
String Telescope Concepts
Truss Tube to String Telescope Conversion
Greg's Right Angle Telrad
Please contact me with any comments or questions. firstname.lastname@example.org