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50.8mm, 50mm, 2" filters???


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I'm thinking about stepping up the filter size, but I'm at loss regarding the many different sizes around the 2" mark...

The new Atik EFW3 comes with wheels in either 2" or 50.8mm according to FLO. To me that's pretty much the same dimension. Astrodon sell 50mm unmounted, so what version of this FW would I need?


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You get slightly more clear aperture with the 'unmounted 2 inch' option. The threaded filter holders of the 'mounted' variety eat slightly into the aperture. We have both systems parallel here in the dual Tak106 rig at F5. To be honest the difference is not that great and not enough to worry about, but unmounted would be the better choice. At F7 on the TEC 140 there is almost no vignetting with the 2 inch mounted.

Of greater significance is the fact that Astrodon don't do 2 inch mounted, so if you want to go for their NB filters this is the carousel you'll need. 

I only know these setups as '2 inch mounted' and '2 inch unmounted' so I'm not sure which is which in mm but I suppose the unmounted are the slightly larger ones. Do check that!!!


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12 minutes ago, ollypenrice said:

Do check that!!!

Yes indeed!


I'm confused by the options here. Giving it another thought I realize that 2" is 50.08mm and not 50.8mm but that hasn't solved the mystery.

All I ever used was 1" or 2" mounted filters. Gives me something to hold on to as I handle them...


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