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Old 03-06-2021, 03:40 PM
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Merlin66 (Ken)
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Merlin66 is offline
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 8,328
Solar imaging -various cameras v's Newton Rings

Over the years I've used various cameras for solar imaging. Started in White Light, then Ha single stack, later double stack and more recently CaK.
Due to me seeing down here on the Bellarine I use ED80s with x2 or x2.5 barlows/ PM. this gives me around f18 to f20.
I've gravitated to the ASI 1600, (which replaced a "defective -for solar imaging", ASI 183) for both White Light and CaK. Normal sampling around 0.8 arcsec/pixel.
For Ha (DS at 0.4A) I found initially the ASI 174 gave poor sampling, hence the change to the ASI 1600. I've battled Newton Rings with the ASI 1600 for a while. Tried various flat filter stacks and the obvious T2 tilter, both with limited success.
After a couple of frustrating sessions I went back and tried the ASI 174 - the sampling may not be ideal but it did not suffer from the dreaded NR.

I also have an ASI 178 (2.4 micron), which I hadn't tried on solar....i was impressed! the 5 x 7.4mm chip at prime focus of the ED80 gave a bit over 80% disk coverage and.....no NR!

OK, two solutions for Ha -the ASI 174 or the ASI 178.

How to get rid of those NR with the ASI 1600 - is it even possible??
I tried various tilt settings once again on the ZWO T2 tilter, up to the max of the adjustment screws. This was a tilt of 1.8 degree. Still NR!
In frustration, I removed the ZWO screws and replaced them with much longer M3 screws from the workshop.
The first setting was way overboard, but what the hell...well, well, well after some re-focusing there were NO NR visible on the full disk image.
I figured the "best" solution lay between my excessive tilt (3.2 degree) and the ZWO max of 1.8 degree.
It took a few twiddle, image, check sessions to find a "minimum" tilt angle for the ASI 1600 where no NR were visible..for my camera and set-up this turned out to be 2.6 degree.

I now appear to have a working solution to the ASI 1600 used on the Ha DS set-up.

Any of the cameras - ASI 1600, ASI 174 or ASI 178 for WL or CaK
For Ha, ASI 174, ASI 178 or ASI 1600 (with 2.6 degree tilt)
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