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  #18  
Old 08-02-2014, 12:53 PM
glend (Glen)
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Join Date: Jun 2013
Location: Lake Macquarie
Posts: 7,121
Thanks for that Don, it is very useful. So my 102mm/600mmFl F5.9 refractor is in the range of filterable, that's good news. When you say an f6 will "need alot" what exactly does that mean in terms of these cutoff numbers?
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