I’ve come up with this test report of Optolong and ZWO filters not only because we are the main Optolong importers and ZWO distributor in the UK, but because I myself also wanted to see what we sell and whether we should expect any problems, which is of course very important if one wanted happy customers… It was also a response to an article I read on the Cloudy Nights forum: https://www.cloudynights.com/topic/602155-testing-optolong-and-baader-narrow-band-ha-sii-filter/ As you will see this is not a quantitative report, but it will show the tendency and that Optolong and ZWO had good intentions and made positive improvements and that it is safe to buy their filters that were manufactured comparatively recently (i.e.… Read more »