Backyard Astronomy


Flat-Field Light Box

In the spring of 2008 I took one more step toward my goal of total remote control of the observatory equipment. I rebuilt a light box originally constructed for a 9¼" SCT so it would work with my 130 mm APO, and be bright enough to allow short exposures. In addition, I attached the light box to a wall partition using Velcro, so when the mount is parked, the telescope points at the light box, as shown in this photo.

Light Box

I replaced the original white LEDs with four super-bright one-watt white LEDs made by Liteon (part number LOPL-E011M). These LEDs truly are super-bright! A flat frame with the luminance filter requires an exposure of only 0.4 seconds (unbinned), and with the hydrogen-alpha filter, the exposure is just 10 seconds. These exposure times are on the order of 5% of those required using the original LEDs. Needless to say, I'm very pleased.

The frosting on the cake is that I can switch the light box on and off remotely, using the Ethernet power controllers shown here. Now all I have to do to take flat frames is to park the mount, turn on the light box, and start exposing.

This photo shows a close-up of one super-bright LED. It's mounted on a circuit board and uses a 10 Ohm 1 Watt current-limiting resistor. All four LEDs are powered from a 6-volt regulated DC power supply. Each LED draws 290 milliamps, for a total of 1.16 amps from the power supply. Here is the circuit board artwork (pdf, 111KB), should you want to make your own.

Light Box LED

As this photo shows, each LED is aimed toward a corner reflector/diffuser, not directly toward the rear panel of the light box. In addition, a baffle blocks side-light from the LED that created hotspots on the rear panel. The light box is about 14" square and is 6½" deep from the front to the rear panel.

Light Box LED

Updated September 7, 2016