19.10.19 Vignetting continued.

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Saturday: The sun showed for only a short while. My 6" f/8 has a solar, light cone diameter of about 30mm at the etalon group 200mm inside focus. I also confirmed 11-12mm Ø at focus. Which suggests that much of the light never enters the 20mm Ø etalon. The front AOK, etalon adapter has an internal baffle which could be "borrowed" to support the GPC.

I mocked up a few OTA light cones with two straight edges. Only a 50mm f/10 has a solar, light cone small enough @ 20mm Ø at 200mm from focus to pass through the PST etalon. Every aperture larger than this will throw a large light annulus [halo] around the etalon.

I checked a 60mm f/10, 90mm f/10, 120mm f/10 and a 150mm f/10. Each, in turn, throws a bigger halo around the etalon. It is obvious that solar disk image size increases with focal length. Each increase in aperture at f/10 will increase the focal length. Image size = FL/109.

The obvious question is whether this matters. Does heavy, mechanical vignetting affect image resolution? Can we go on adding aperture, ad-lib and gain resolution with each step up in objective size? It would seem so. I intend to try some small baffle stops in front of the etalon to see if can easily detect any difference in the image.

Sunday: Trimmed the veranda doors and then continued with the dome chain drive. I used a piece of thin plywood as a pattern to save wasting aluminium plate.  It is a struggle to achieve the correct angle so that the friction wheel remains perfectly tangential to the dome base ring. If it isn't tangential it steers the dome in or out at that point. When the crank was at the SE corner I must have hit the right spot by accident. I am struggling to avoid a tight spot in the new position. I have marked all the steering and support rollers so I can monitor, from a distance, whether they are turning. Brief watery sunshine around lunch time but not enough to be useful.

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