A laptop computer is a great companion to your telescope but you'd better protect it from dew. You'll also need to shield the light so it won't annoy others (as well as cover the screen with a red filter). The following instructions will help you build a custom dew and light shield that folds flat for storage.
Corrugated Plastic Sheet
Do not use cardboard or foam poster board as they will sag after they get wet. Pictured at right is corrugated plastic sheet which is readily available at most hardware stores. It's commonly used for campaign signs so if you have a few leftover from the last election just spray paint over the graphics.
Paint the inside flat black to prevent screen light being reflected toward others.
Clear Heavy Duty tape works well and is almost invisible.
Fastens the sides of the enclosure when in use and allows easy folding for storage.
Red Filter Material
While not really part of the dew shield, you should cover the laptop screen with transparent red material. Sloan's Woodshop carries 1/16" thick plexiglass and #997 Red works really well.
The first step is the hardest, deciding how big to make your enclosure. Start with your laptop set up exactly the way you'll use it at the telescope ... put it on the same table, sit in the same chair, tilt the display to the same angle you'll use, use a mouse if you'll use one, and plug in whatever cables will be used in the field. Resist the temptation to make it large, it is better to keep it just large enough to meet your needs. Don't put anything within the enclosure that isn't really needed (the power supply or serial adapter can usually go under the table instead of inside the enclosure).
Start by placing panels of corrugated plastic along each side of the laptop working area. Use the computer a bit and make sure you have enough working room. This will be the W dimension of the back and top panels.
Next place a panel of corrugated plastic resting on the top of the LCD screen and with the front edge directly above the front edge of the computer. This is the minimum depth of the enclosure which will shield it from dew. While sitting in the chair and viewing the computer screen, raise the front edge of the panel until it does not block your view of the computer screen. Now visualize how big the enclosure would be if this were the top. Now raise the front edge of the panel higher and bring it toward you while visualizing the increase in enclosure size. The further you bring the front edge of the panel toward you the better you'll protect the computer from dew, but you'll also have to raise it higher to prevent it blocking your view of the screen. You'll have to determine for yourself what is the best tradeoff. You have now determined dimension T of the top and side panels.
While performing step 3 the panel rested on the top of the LCD screen, however it is best to elevate it about one inch. So for dimension R it is suggested that you add one inch to the height of the LCD screen.
We must now determine the depth of the bottom of the enclosure. It must be at least the depth of the laptop, but I recommend adding a few extra inches. This will make the side panels angle forward at the bottom. When you determine this point, measure from it to the rear of the side panel (dimensions B) and also to the front edge of the top panel (dimension F).
We are now ready to cut the panels. If you have some cardboard lying around you may wish to make a mockup first to insure you are happy with the dimensions.
Cut the top and back panels to the dimensions shown. All corners are 90 degree right angles.
Cut the first side panel as follows:
Start from the corner where B and R meet. This is the only 90 degree right angle.
Mark lines for dimensions B and R.
From the corner B - F measure off dimension F. Then from corner R - T measure off dimension T. The point where these two dimensions meet is corner F - T and you should mark a dot at this location.
Now measure between the 4 corners to insure all dimensions are correct. Then draw lines and cut the first side panel.
Using the first side panel (flipped over to its back side) as a template, mark and cut the second side panel. This insures that the two are identical.
At this point I would suggest painting the interior of the panels black. This will prevent reflected light from bothering other observers.
Lay out the panels as shown above with the inside surfaces up.
Butt the edges of the Top an Back panels together and apply tape to the seam. Use several layers to give the joint some strength.
Fold the Back panel onto the Top panel (the taped seam acts as a hinge) and apply tape around the edges. You have now formed a hinge that allows the panel to be folded for storage.
Flip the panel over so the outside surfaces are face up. The Left panel should be on the left side as shown below.
Butt the side panels against the Top panel and apply several layers of tape to each seam.
Fold the Left panel onto the Top panel as shown below.
Apply tape around the edges forming a hinge.
Fold the Right panel onto the Top panel as shown below.
Apply tape around the edges forming a hinge.
Now unfold the panels.
Apply Velcro to the lower rear corners as show in the photos above. This will hold the enclosure firmly when in use yet allow you to easily fold it up flat for storage.
Copyright 2018 by Ronald & Teresa Keating. All Rights Reserved.