Quote:
Originally Posted by CalvinKlein
I guess a doublet would be quite adequate for narrowband imaging where you are more than likely re-focussing for the different filters. I might have to give my very 'eavy, very 'umble 500/102 achromat a go with NB
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True, but there is still out of band signal leaking through even the best narrowband filters during longer exposures - it was readily visible around brighter stars with my ED doublet and 3nm Astrodons, so I would expect significant halos around brighter stars with achromat even with the best 3nm filters, and sharpness will most likely be also reduced in the extended objects.