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Message: <blockquote data-quote="denco@comcast.n" data-source="post: 1428151" data-attributes="member: 25300">Without having to sign up to the Astromart forum what are the components of FK61. Does it specify this in the article? Does it say what type of ED glass has the best performance when dealing with CA. Does all ED glass contain some small percentage of fluorite crystals like the Zeiss FL or do they use something else in their chemistry. It sound like pure crystalline fluorite is one of the better performers when it comes to controlling CA in lenses from my Astromart article. An interesting topic and I am sure Roland Christen would know quite a bit about it. I would really be interested to see how the Chinese ED glass compares to say the glass used in AP telescopes. Dennis</blockquote>