15.07.2021 PST etalon adjustment.

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Thursday 15th 73F and climbing quickly. Bright but with a milky and cloudy sky. 

As I struggle with the ring-shaped sweet spot on my PST etalon I plan to experiment further.

I shall try different spacing for the etalon from the focal plane. Just to see if affects anything. 

10.07  First image in soft and mobile seeing conditions. Large, 912x912 frame size to check lighting and being on-band across the entire image. Lower right quadrant is brighter and off-band.

With an 800x800 frame size I then tried several etalon distances inside and outside of the standard 200mm inside focus rule. There were variations but none of the resulting images was superior. No easy fix there.

10.50 >After much adjustments without improvement I placed the Baader 1.125 GPC in front of the etalon. No GPC in front of the camera. Had to add an extension and focus out 10mm. Brightness asymmetry continues.

 

11.24 Removed the 1.125 GPC and fitted the 2x GPC on the camera  for a wider field at 800x800. During the process the etalon was rotated by 90°. Resulting in a diagonal, dark bar at 90° to earlier images.

 

 

 

 

11.48 I wrapped the etalon in PTFE tape and changed to the 2.6x GPC. Slightly better?

In theory it would be possible to make a mosaic with the etalon at right angles for the second capture. This might spread the etalon ring-shaped, sweet spot.

 

 

 

 

 

12.20 An interesting chain of filaments. 

 

 

18.59 Last image of the day in mushy seeing conditions. Captured at 800x800 and cropped. The brightness asymmetry never vanished.

I was becoming irritated by the constant stalling of the drives during slews. So I removed the complete RA motor and worm housing. It seemed the ball thrust bearings, which I had exchanged for the normal races were causing too much friction. 

I removed the drive belt and was startled at the variation in friction when the worm was turned in my fingers by its large, timing pulley. I am going to look at plating the ends of the worm housings. I had been using screws with oversized washers to retain the bearings and provide some end loading. 

I made a new, much thinner packing washer in the lathe. Friction seems much more even now. Without the previous end float. [Backlash!]

 15.00. Had to give up because of the heat and poor seeing conditions. 85F in the dome. 82F outside. I ought to get a small desk fan to move some air.

 

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