|
Stars still pass through Ha filters due to their inherent brightness, I've imaged using a 13nm Astronomic, a 7nm Baader and a 3nm Astrodon, I can tell you right now, the 3nm is a pain in the backside to focus, the 7nm is doable on anything brighter than say, Mag 5, the 13nm I would rarely bother to slew to a brighter star to focus, I could almost always find a star bright enough to evaluate focus within the field of view of a given target..
A 7 and 13nm Ha filter also let in NII, Close SII and a few other emission lines, a 3nm lets only Ha pass. they are almost infuriating to focus... I use up to 10sec focus exposures on a mag 2 star at 3nm, otherwise maximDL's autofocus routine will fail... in any uniform star field, it can be up to 30 seconds before you actually start to see stars...
|