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
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
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
Butt the edges of the Top an Back panels together and
apply tape to the seam. Use several layers to give the joint
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
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.
The "Set & Forget" Precision Thermostatic Dew-Heater Controller
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Copyright 2014 by
Ronald J. Keating, Jr.
All Rights Reserved.