Why I bought the ten position filter wheel was the availability of a Nitrogen [NII] 3nm filter. The continuum 5nm red filter also looked useful for reducing NB flare etc around bright stars.
Here is an explanation how a 5nm or wider HA filter covers both HA and [NII]. The detail in HA images can be due to Nitrogen at 658.4nm [NII].
http://dg-imaging.astrodon.com/galle....cfm?imgID=148
For more info on Astrodon NB filters see here.
http://www.astrodon.com/products/filters/narrowband/
When I ordered the Astrodon filters the 3nm [NII] and continuum were not in stock. I will get them when they are available.
Should make for interesting NB images when there is little or no SiII 671.6nm.
Any thoughts on this?
Below is M27 with four NB filters from Astrodons site.
Bert