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Samir, If you are willing to make a comparison of the 13 and 6nm filters I just picked up a Canon EF 200mm f/2.8L II USM Lens. I believe you also have this lens. Lets pick a target, iso number and length of subs ect. Perhaps not a perfect test but it might be fun.

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Hi, it's actually that specific lens (and others) that have steered me towards a pop-in, clip filter. As I said, it's a very looong story. Used to be that the only pop-in Ha filter available was a Hutech, but that had to be used with a UV/IR blocker (because it leaked some IR). My DSLR at the time had clear glass. When I acquired another modded DSLR (with UV/IR blocker) Hutech had stopped selling the filters. So I bought the Baader 7nm 2" Ha. An excellent filter, narrower than my 13nm Astronomik. At the time Astronomik had problems with manufacturing their 6nm Ha, even though they were still being advertised. I was in correspondence with the owner of Astronomik. When they finally sorted out the fabrication issues, they also offered a pop-in version. This was a godsend! Usable with the 200mm lens wide open (also with all my lenses from 14mm to 600mm). The difference between the 6nm and the 13nm is actually immediately obvious. The image through the viewfinder is much dimmer, and autofocus is rarely possible with the 6nm. Last time I autofocused on a street light about a mile away. I do have an image with the Astronomik 13nm and the 200mm lens here but not much use for comparison. Like most stuff in astrophotography, without a controlled, side-by-side comparison one can easily end up with the wrong conclusions. Stuff like light pollution and post processing are very critical. Of course, just being able to use your 200mm lens at f2.8 instead of f4.5 (2" filter attached at the front of the 200mm lens with step-down rings) is worth quite a bit. So far the only nagging issue I have experienced was that in a C14 Hyperstar the Astronomik clip filter showed more flare from bright stars than my 2" Baader, but I had not used both filtyers on the same star field; so was it the star field that had much brighter stars? or the filters? I doubt that the flare had anything to do with the filters, but if somebody reports something similar then it would be worth examining.

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