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- GSO 8-inch TRUE CASSEGRAIN
CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Building a Cheap Effective Light Shield
Like many amateur astronomers, I suffer from a light polluted neighborhood environment. We have a street lamp to the southeast, all night spots on houses to the south, southwest, and northwest. My house blocks all light from the north and east.
When I can get fully dark adapted, I can see magnitude 5.2 stars from this site so the sky can be seen reasonably well if the light trespass from the neighbors can be blocked. In addition cars pass by at irregular intervals. To stop the light trespass, I have built 6.5'x 5' light shields at a cost of about $10-15 each. The first one is somewhat more expensive since you may have to buy the "general equipment". Each takes 1.5-2 hours to build if all parts are present. I chose this size as it is easy to get in and out of my garage door. The shields nest and take up only a little room in the garage. If you follow the gluing instructions, they can be easily disassembled for transport.
Initially, three of these devices have been successful at shielding me from all of the lights above and all car lights going by my house. I can now remain with dark adapted eyes for hours in my neighborhood. Ultimately, I made 6 and now have a 12x16 "dark room" in my front yard. I can do reasonable astrophotography from within.
If you look carefully at the pictures, you will notice that the design for holding the plastic sheeting has evolved from rubberbands and clamps, to Velcro. All of the designs work reasonably well, including the ones suggested by users below. Each has its own little problems:
Rubberbands deteriorate over about a year and need to be replaced.
The Velcro glue is inadequate to handle heat and cold. I used "Duro" brand contact cement to stick the Velcro to the PVC. It has held for several years. On the plastic sheeting side, I use staples to secure the Velcro.[staples.jpg]
Using duct tape as suggested below works well, but the shield cannot be taken apart readily for travel.
If you try the plastic bag idea, I would love to hear from you. I can't imagine trying to get it over the top.
Clear (and dark) skies!
To build a 6.5 foot x 5 foot light shield, you need the following:
General equipment: [parts.jpg]
Can of PVC cement $4.95 (good to make many light shields) --see Jim McKay's comments
1 roll (10ft x25 ft) of 3 mill black plastic sheeting (enough for 8 shields) $.4.95 Some of the black plastic I saw was not opaque and let a little light through. Check that it is opaque before you buy.
Hack saw $8.95
1 bag sturdy 7" circumference rubber bands (cheap?). (needed to hold velcro on while glue dries)
For each shield you need the following:
- 3 x10ft pieces of 1" PVC pipe $1.48 each ($4.44 total)
- 4 x1" PVC Tees $0.88 each ($3.52)
- 2 x" PVC 90 degree elbows $0.78 each ($1.56)
- 12 Medium (1.25" wide) binder clips ($2.59) (not needed if Velcro is used)
- 15 inches of Velcro tape (not needed if binder clips are used)
Note: ¾ inch PVC pipe is too small and a bit too flexible. I have made successful ones with 1" and 1.25" PVC. 1" is my preference.
- Cut 1 PVC pipe into 2 x 5'0" pieces
- Cut 5'7' pieces from the other two 10 foot pipes
- From one of the 4 ' 5" remnants, cut 2 x 6" pieces and 3 x 1 foot pieces
- From the second remnant, cut 1 additional 1 foot piece
- Glue 90 degree elbows to each end of 5 foot section (be sure they point same way (Piece #1)
- Glue the center hole of tee to each end of the other 5 foot section (be sure that they line up parallel as in picture; see Jim McKay's note) (Piece #2)
- Glue 2 1 foot section in to ends of 3rd tee
- Glue 2 1 foot section in to ends of 4th tee
- Glue 6 " piece into center hole of parts from step 3 and 4 (Piece #3 and #4)
The two 5'7" pieces are pieces 5 and 6.
Once the glue has dried, the frame is assembled. I put a very small amount of grease on the unglued joints to be sure I can easily separate them when desired.
Attach 4 clips to the top (piece 1) and the sides (pieces 5 and 6) using the rubber bands and space about equally. (I usually run the rubber band through the handle on the clip and then wrap both sides over the tube). In this way the clips are tight enough not to move about on the tube.
Alternatively, use a good contact cement (paint on both the pipe and back of Velcro, allow to get tacky, and press together). A rubber band is useful to hold the Velcro fast until it has completed the drying process.
Assemble the frame as in the pictures. Here is a picture of a completed single frame unit.
Cut a 6 foot piece of the black plastic off the roll. Hang the strip (it is 10 foot wide) over the frame so that both sides are equal. Cut the plastic sheet in half. This gives you two 6 foot x 5 foot sheets. Clip one of the sheets (five foot part horizontal) to all 12 clips and your light shield is complete. You may or may not wish to trim the bottom inch or two off the bottom of the sheet. (mine drag the ground by about an inch and keep ground level light our nicely.
Connecting 2 light shields
Two light shields can be hooked together by building a modified foot. A picture of the double foot is shown, and a 3-6" central pipe can be used. At 5" (shown) light coming through the edge of one light shield is blocked by the second. To use this you remove the single feet from one side of each light shield and plug in the double foot.
Suggestions from people who have done the project:
After this was originally published, several suggestions have been made. One user replaced the clips with duct tape. This works but the device is less portable.
Another user suggested that you use a heat gun or hot glue gun to seal two plastic sheets together to make a bag that can be slipped over the support.
Jim McKay wrote:
Thanks for posting the plans for building the light shield. I've built two to help block the light from two sources and they have been very handy. I just wanted to point out a couple a things that I discovered along the way.
The pvc glue set up faster than you think. It is very important that you trial-fit the pieces that are being glued together and mark them for proper orientation before you put the glue on. I initially thought that there would be some time to move them around before the glue set up, but I was surprised to find out how fast the stuff sets up. Luckily, the pieces were in fairly good alignment. I was more careful with the rest.
The plastic sheeting that I was able to find was slightly thicker than the sheet that you used and I consequently found that the binder clamps wouldn't hold on to it tight enough. I ended up getting some 5/32" rubber vacuum/windshield washer hose from an automotive parts store and cutting small lengths of it, slitting it along one side and sliding it over one end of the binder clips. This held the plastic pretty tightly and it no longer slipped out of the clips. Prior to using the rubber hose I did try putting little pads of hot glue on the plastic sheet and that worked also.
Many thanks for putting up the plans.
- DHEB likes this