An astronomy-centric posting of a reasonable solution to a common observing problem we have at Darling Hill Observatory. Between the amateur astronomers who live and die by go-to scopes and the purists who rely on memorization (and occasional luck) lie those of us with non-automated scopes (and binoculars) but finite amounts of time at night. The quick solution is a notebook (such as my workhorse MacBook Pro) and any one of a number of astronomy programs, be they free (and very good) open source programs like Celestia or the ever-updating Starry Night Pro. The problem, of course, is the tendency of laptop screens and all of those bright little LEDs to completely ruin night vision. The solutions are red acetate covers (the same ones used to cover flashlights, observatory lights, and anything else glowing at the Observatory).
The problem I had looking around online for such covers was the inability to find the "just right" acetate weight, such that the screen is sufficiently red but bright enough to not spend additional time squinting at the computer screen after squinting in the eyepiece. The roll-your-own solution (with a few nice features) involves two sheets of acetate and a roll of 2" gaffer tape.
The procedure is simple enough (click for larger images if any need for clarification).
1. Start with two pieces of 18" x 24" (0.005) Red Transparent Clearlay (acetate). The size is important, as the folded and taped result makes for a perfectly-sized sliding cover on a 15" MacBook Pro (and you can adjust to taste for other laptops). If you're in the Syracuse area, you'll find this acetate at Commercial Art Supply (way in the back) for around $4.00/sheet.
2. Fold both in half (now 12" x 18") as evenly as possible, preferably with your favorite astronomy picture book.
3. Gaffer Tape. The joy of gaffer tape. NOT duct tape. Gaffer tape (to the uninitiated) is a cotton-based pressure-sensitive tape that sticks to itself beautifully with the strength of duct tape but without the smell of duct tape. Drummers will have plenty left over from muting toms. Again, you can find gaffer tape at about $10/roll at Commercial Art Supply (well worth it in the long run). In order to make the two sheets of acetate stay together, run one pass of gaffer tape around the outside of the crease of one sheet of acetate…
4. …then place this sheet of acetate within the second sheet and run two more passes around the crease of the outer sheet. It is important to not use too much tape in this cover to keep the weight down (you will be using this in pitch black conditions and will invariably tip your laptop over. Don't make it even easier on yourself).
5. The taped pair will look as such. Make the final tape wrap shorter than the thickness of the tape (so the perpendicular pieces cover the exposed end).
6. One piece of edge tape on each side wrapped around front and back to close them off.
7. The final step is to tape around the sides. This is the important customizing last step, as you can adjust the fit of the cover for your laptop screen. Slide the cover over your screen and pinch both sides until the cover is snug. Then, simply wrap the tape around the sides twice (once may be too easily ripped, more than two is just excess weight) such that the tape lines up with the pinch marks. In the case of a 15" Macbook Pro, 18" x 24" acetate and 2" wide gaffers tape make for a perfect fit by taping up to the outer edges.
8. Final product. Three sides covered by gaffers tape, the bottom is four edges and three pockets.
Four edges and three pockets. Simplicity itself. This provides you with a way to adjust the amount of screen reddening without adjusting the screen brightness. The series below shows increasing screen covering in an instance of Starry Night Pro, including the uncovered screen, the three pockets, and simply placing the whole cover over the screen.