LED Astronomer's Flashlight for under $5
I have found that purchased astronomer's red flashlights are too bright. With less than $5 in parts I built a small, dim LED flashlight.
I settled on a 680 ohm resistor for backyard viewing inside the city (neighborhood lights, etc.). A higher resistance resistor (dimmer LED lamp) is more appropriate for dark sky viewing.
Battery Holder with built-in switch: Radio Shack #270-409
5mm Wide-Angle red LED, 1.7 volt, 20mA, 800 mcd: Radio Shack 276-309
Resistor: 680 ohms (higher resistance for dark sky use), 1/4 watt.
Open up the battery holder (must remove a screw).
Remove the screw from the little cover at the switch end of the battery holder. Note that the cover is heat-welded in place, so you need to use a knife to break the heat welds.
See the position of the resistor and LED.
Drill a hole for the LED in the location shown. Make sure the hole is a little small so that the LED will have a snug fit.
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