28.01.2020 Dew heating bands and new tube rings.

*

I was losing so much precious imaging time to dewed objectives, that I decided to invest in combating the problem. While the secondhand hairdrier works well on the front of the lenses it had zero effect on the rear element. I was spending half an hour on full heat warming the objective cell area. So I bought two Astrozap heating bands. One of 6" and one of 7" plus a 4 port HitechAstro controller. The controller came with a cigarette lighter plug. So I also had to buy a 12V 5A PS with cigarette lighter socket.

It all seemed to work. Though the heating effect is very subtle and slow to build up at half max setting on the control knobs. No heat at all from the bands at 1/4 setting despite the red LEDs being brightly lit. The Astrozap bands are both generous in length. As were the cables with each component.

I'll leave it all on at half way and then try it on full to see if things get warmer over a longer time.

5 minutes later: Full on does feel warm now. The heating effect is very centralized on the internal, plastic band. Presumably the outer band will insulate the heating area from the cold air. So this will help to contain and spread the heat. I can only just feel some warmth in the middle of the inner, plastic strip at a 10-to setting.

The 160mm Skywatcher tube rings turned up in the post. These proved to be too small for the thumbscrews to meet properly when wrapped around my 162mm OD main tube. So I had to clamp the joints with setscrews instead of the original chrome knobs. The tube seam fitted at the ring opening. I used stainless steel, hex socket head screws but longer thumbscrews would be far more preferable. One doesn't want to be messing about with Allen [hex] keys when a telescope is dangling from open tube rings high above one's head!

The thread near the screw head needs to be relieved to work properly. You can't tighten something together which has a thread in each half. This is why the original thumbscrews have a smaller, plain shank below the enlarged head. This necessary freedom in the shank also allow the screw to be self-aligning as the two, ring halves close together. The larger, threaded section also maintains captivity when the screw lies only in one half of the ring.

 *