I just whipped up my first dew shield for my 8" SCT, and figured I would share a little about the process and a few things I might improve the next time around.
Lots of folks have posted about using reflective insulation (basically just mylar bubble wrap) under the Reflectix brand for dew shields. I managed to find some at a local Ace Hardware in a 16" x 25ft roll for about $20. Lowe's and Home Depot also carry it on their website, but they didn't have it in-store. I saw a different, cheaper brand at HD, but I'm glad I got the Reflectix brand. It feels a little stiffer and sturdier, so it shouldn't sag under its own weight like the cheaper stuff might. Overall, I utilized:
- Reflectix 16" x 25ft reflective insulation (I only used about 36" or so of the stuff.)
- Gorilla Glue heavy-duty spray adhesive - 4oz (Walmart craft section)
- Black felt (Walmart fabric section)
- Gorilla Glue (Walmart hardware section)
- Black hook-and-loop tape (I had this from another project)
To make the dew shield, I wrapped the front of the scope in the insulation to get an idea of circumference, and then added a couple of inches to it. Then, I cut a slot in one side to fit past my Losmandy radius block on the front of the scope. This served a couple purposes: 1. It obviously just makes it fit deeper onto the front of the scope for stability. 2. It hooks the dew shield around that radius block to secure it so it cannot blow or fall off. I also used spray adhesive to add a 1.5" wide strip of additional insulation to the edge of the insulation. Once the dew shield is attached over my dew heater, it'll have a nice even fit. And the 16" width of the material has about a 4" overlap with the scope, so it fits the typical (diameter * 1.5) ratio for the shield length at about 12" of extension from the end of the scope.
After cutting the slot, I used the spray adhesive to attach the black felt to the insulation. I sprayed the insulation at angles from the center out toward the edges to avoid getting adhesive on the edges and having it stick to things. If I did this again, I would even spray the edges. I'd cut the black felt a bit longer and then wrap it around the back side of the insulation. I was able to do this in some areas, but not others, as I didn't leave enough fabric there. I added a strip of black felt to help cover the exposed edge of the insulation where it meets along the length of the tube.
I used Gorilla Glue to adhere the hook-and-loop tape in a full strip to completely wrap around the scope. I didn't want it coming loose at all, so wrapping a full circle around the scope should keep things secure. We'll see if the glue adheres for the long run.
I experimented with sewing 1/2" wide hook-and-loop strips along the long edges where the insulation meets again. This lets me seal that edge and prevent any light or thermal leaks, but I can peel it open and roll up the dew shield for compact transport. This worked surprisingly-well. I'd suggest a heavy-duty needle in your sewing machine for something like denim or heavier material. But, I was able to sew the strips right to the edges of the material and it turned out pretty good. I may sew the long strip that wraps around the entire scope at some point, if the Gorilla Glue begins to fail.
If I make another dew shield, I would make the black felt oversized so I could wrap it an inch or two around the outside of the insulation and cover up all the edges, maybe even running a single line of stitching to keep the edges secured to the insulation so they don't peel up if the spray adhesive fails. I'd also just sew on all of the hook-and-loop strips and skip the glue. Overall, though, I'm pretty happy with how this turned out.
Edited by Noobulosity, 15 November 2019 - 01:32 PM.