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Old 07-05-2021, 06:12 PM
kosborn (Kevin)
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kosborn is offline
Join Date: Mar 2018
Location: Canberra
Posts: 375
HI Alex,

I started with 31mm ZWO narrowband filters with an ASI1600mm and found there were horrible internal reflections as the filters are anti-reflective on one side only. I ended up replacing them with Astronomik filters which work really well. From the reading I've done, 31mm filters are the smallest possible for the ASI2600mm, depending on your focal length. Probably 2" is the best way to go. This web page: has a good calculator to work out minimum filter size for your set up.

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