ATM part 5 – dew protect on secondairy & flocking
Yesterday I crafted a simple dew-buster for the secondairy mirror in my 8″ dobsonian. It’s a tube OTA so the secondairy doesn’t really fog up that quickly but I did need a way to burn away any dew that might get to it eventually.
The plan was quite simple: I would glue some NiChrome wire to the back of the little mirror with silicone kit and solder the ends to a holder for 2 recharchable AA batteries. That’s 2.4V to work with so I’d have to stick a little under 30cm’s of the wire onto the backside of the mirror. This would then give off ~1.6 Watts of power and that was in theory easily sufficient for this mirror size.
Yesterday I took the soldering iron to hand and made it work. Well, it didn’t at first. Apparently you have to sand the tips of the NiChrome wire first to remove the gold coating. This coating is not conductive so no electricity was getting through the wire at first. So I sanded the NiChrome wire, and resoldered the electricity wires back on. After this little rework the mirror warmed up quite nicely. Dew-buster ready!
Removing the spider vane to do all this also gave me the chance to flock the inside of the cardboard, and actually quite shiny, OTA. I always use velours for this. The lower end of the tube will be done at a later time when the primary mirror is out for a new coat. For now it is a nice improvement. #smallsteps
After putting the secondairy back in I had to collimate the telescope. Luckily the cheshire I ordered two weeks ago on AliExpress also arrived yesterday! A cheshire is a simple device and I gathered I’d try one for under €20 from AliExpress. Buying one here in the shops will set you back at least €35 so I went for the el cheapo option. It worked. The cheshire looks fine and perfectly usable.
Next up in ATM’ing my dobsionian is having a new coat on the primary mirror applied by Sterrenwacht Almere. But this I will do not before August. The views are sufficient even with the damaged coating.