NII extraction from Ha data?

[Adam J]

So have been thinking about doing a duel imaging rig and one of the things i was mulling over is a second Ha filter to go with that (on paper at least)

So if I have a Astrodon 5nm Ha in one scope and a Astrodon 3nm Ha in the other could I take the difference between the 3nm and 5nm and in effect extract the NII channel from that delta?

Any thoughts?

Adam

[newbie alert]

It would be interesting to see the difference between the 2...

[The Lazy Astronomer]

3 hours ago, Adam J said:

duel imaging rig

I think mr Spielberg beat you to it 😁

Sorry, childish, but couldn't resist.

On topic: l can't see why this wouldn't work in principle. The 3nm Ha seems to transmit around 30% NII, so I guess you'd be be looking at an effective transmission of around 65% NII once subtracted.

Like everything in this hobby, I suspect in practice it might not be as simple as it first appears. Personally, I'd probably opt for a dedicated NII filter if NII imaging was my aim. 

[Adam J]

14 hours ago, The Lazy Astronomer said:

I think mr Spielberg beat you to it 😁

Sorry, childish, but couldn't resist.

On topic: l can't see why this wouldn't work in principle. The 3nm Ha seems to transmit around 30% NII, so I guess you'd be be looking at an effective transmission of around 65% NII once subtracted.

Like everything in this hobby, I suspect in practice it might not be as simple as it first appears. Personally, I'd probably opt for a dedicated NII filter if NII imaging was my aim. 

NII imaging is not my aim, more wondering if it might be a useful side effect that would push me to get a 3nm instead of a second 5nm. 

Adam