30.03.2020 PST Etalon tuning. New AR on NE limb!

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Monday 30th, 47/44F, The wind has dropped but there is rather a lot of cloud coming from the north east. The forecast is full sun later.

11:10 Already set up with the open etalon available for the full tuning range. Not enough sunny periods to do more than center and focus the 120MC camera so far.  

11:20 A bit more sun. Changed to the ASI174 Mono camera. Discovered there is no extreme range of etalon tuning. The tuning adjustment disk hits the top plate [with its negative lens] on the rise. Which limits the adjustment in that direction. Going downwards there is an obvious limit to compression when the torque required to tune increases rapidly.

There is a severe asymmetry to the brightness of the sun's disk. This changes with tuning but cannot be eliminated. It is also very dependent on frame size.

The next question is whether the etalon is optically symmetrical. Is there a best orientation? The sponge ring has left a slight surface mark on the etalon. So I, quite naturally, returned it to that position. Assuming that the factory deliberately chose that orientation after testing. Should I try the etalon in reverse? It takes only a few moments to reverse it. I might as well do it now. While I am waiting for all this cloud to clear the sun.

12:00 Marginally better surface definition? The images are with the reversed etalon 640x480 with 2x WO Barlow. SharpCap, AS!2, ImPPG & PhotoFiltre7. Cropped.

1215 Better images with cropping and enlargement for local detail.

12.35 Still lots of cloud with very brief sunshine. Another capture and deliberately sharpened.

14.00 48/43F Back from lunch. Cloud continues to tease but coming from the north east and east now. The forecast is for clear skies after 15.00.

15.00-16.00Continued to capture and process but the seeing wasn't very good. The wind has really picked up too.

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