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Old 27-04-2021, 11:57 AM
ftclausen (Fred)
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ZWO ASI120MC-S and Coronado/Meade PST

I am looking into using the ZWO ASI120MC-S with my existing Coronado PST (using Skywatcher HEQ5 mount). This imager is attractive because I'm just getting started with imaging and is also good for other (night time) Solar System targets using my 6" Newt (Bintel GSO)

However, based on my research, I've found there are some caveats using the ASI120 with a PST:
  1. Attaining focus - it seems focus happens "too deep" in the eyepiece tube
  2. Newton rings - some images have those ring effects

I believe the focus issue can be solved with a Barlow (or part of a Barlow?). Machining my PST is not an option.

For the Newton rings apparently you can tilt the camera slightly to deal with this.

What are people's experience with the ASI120 + PST combo lately? Is it workable?
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Old 27-04-2021, 03:18 PM
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Fred, you wont get Newton rings with a colour camera, what you will get is loss of definition due to the Bayer matrix in the colour camera. I believe that the older PST's have a shorter eyepiece tube and can reach focus with a camera. Using Flats can help with Newton Rings. Maybe a visit to Solar Chat Forum could be an option.

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Old 27-04-2021, 03:22 PM
N1 (Mirko)
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I have had these exact same issues with the Lunt 35Tha and ASI120. Reaching focus was just possible by using the ASI's low profile face plate that came with the camera, and the Newton rings could be reduced by binning and/or barlowing but I liked neither very much. Also, the 120's FoV was just a little too small to fit the full disk. Overall it's manageable but I wasn't overly thrilled. Prom photos are easier with this combo though. And yes, the colour cam may not have the newton ring issue. Ken (Merlin66) is working on the flats solution, so watch his threads too.
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Old 27-04-2021, 04:23 PM
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Merlin66 (Ken)
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I've used many PST's and many cameras, but to be honest I've never tried a OSC camera on solar Ha, so can't say what NR issues you may have.
My experience however, would lead me to agree that the Bayer matrix would suppress the NR at the cost of definition.
My experiences so far with the use of flat on full disk solar images, using the ASI 1600 is proving successful.
See my thread:
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Old 28-04-2021, 08:32 PM
ftclausen (Fred)
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Thanks for the info all! I'll do some careful measuring the confirm what kind of PST I have (I think it is the Meade flavour) and read the usage of flats thread link below.
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pst, zwo

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