*
The cloud is back and the seeing soft and thermally wobbly.
So I used my laser guided thermometer to measure the temperature of the 6" refractor's main tube. It and the sun, are inclined at about 44° at the moment. I measured 90F, 85F, 75F respectively: Behind the objective, in the middle and at the back plate.
The cloth cladding inside the dome shows much the same stratification despite being completely in the shade.
The main tube has been shielded from sun's direct rays by the objective cell. Which has been pointing directly at the sun all day. The air temperature on my desk is 79F. The outside temperature, in the deep shade behind the building, is 69F.
Would adding a small fan help to circulate air within the 20cm/8" Ø main tube? Or would it merely draw dust inside it? To coat the optics with pollen and rural grime!
My 7" f/12 refractor is standing on its dewshield nearby but fully in the shade of the dome. It measures 77F from top to bottom despite reaching well above the dome's base ring. So about the level of the middle of the 6" main tube. Why the difference?
Is a stratified temperature regime within a solar refractor tube beneficial or negative regards internal [instrument] seeing? The full aperture D-ERF should be blocking the heat before it enters the main tube. Though it still passes some heat. Because I can burn myself at focus. With only the Baader D-ERF as a heat blocker.
I have now turned the dome to shade the 6". I will give it some time to cool and then measure its temperature again. Thin steel does/should not hold its heat. It didn't. The temperature has dropped to 77F from top to bottom. So, does this mean the sun is heating the OTA from within? There is no direct connection between the objective cell and the main tube. There is a turned, birch plywood counter cell.
Another ten minutes and the main tube now measures 77, 74 and 73F respectively from top to bottom. Does this represent the stratification of the air inside the dome in the absence of wind? I measured the surface temperature of various bits of bare timber in the construction at 74-70F descending from high up and down towards the floor.
I have been promised my Titebond III wood glue for delivery by the post office tomorrow. So I can start building ribs from all the arcs. The air temperature has shot up this weekend after months of very cool and wet weather. I could have used the Gorilla Glue but have been avoiding it because of the low temperatures. The advice being to avoid temperatures below 55F. The Titebond claims a much better performance when occasionally damp. [Not submerged!]
No comments:
Post a Comment