Well, this Flat-Box is also quite flat, hence the name :-)

It is based on the electroluminescent foil sold by Gerd Neumann from Astronomik. The original foil is way too bright for a flat box - some cameras (like my SXV-M25) do switch download mode around 4-5s exposure, for some cameras with slow mechanical shutter the exposure time has to be significantly less than the shutter time. The Astronomik foil was dimmed by stacking 5 or 6 pieces of quality printing paper (no artifacts, water marks etc) and two layers of milky white ("opal") semi-transparent plastic.

The electroluminescent foil, paper and opal plastic are all attached to small sheet of 5mm "model-grade" plywood. The layers of opal plastic are also separated by small frames made from 5x10mm "model-grade" dovels. Voltage converter and small plastic box where the cable harness was hidden are also attached to the "backbone" plywood. Another piece of 4mm plywood acts as cover protecting the plastic from being scratched in transport.

The entire stack is quite rigid and protects the delicate foil pretty well, while still being very lightweight. OK some weight is also important, as the foil itself while placed on an aperture of my telescope could be easily blown away by a delicate gust of wind (the ad-hoc solution was to place 2 cans of beer on the foil :-). The external dimensions are ca 30 x 30 x 3cm and it fits nicely inside my laptop bag.

The foil shows some bias towards blue, which is OK for CCD cameras more sensitive in red, although I have not tested it yet with Ha filter.