Ha Filters

[mick pinner]

could someone please let me know the difference in imaging between 4Nm and 13Nm Ha filters. thanks.

[gbeal]

Mick,
Not scientifically of course as Kiwis are not overly edumicated but the 4Nm will allow less of the "other" light in, JUST the Ha, whereas the 13Nm will allow a wider selection of light, Ha as well as "normal". Stars will be less visible in the 4, and more in the 13.
I use the Baader 7Nm.
Gary

[Merlin66]

Gary said it all.
Unless there's some new artificial lighting emitting around the Ha wavelength - don't know of any, there's not much else in the sky which gives out light in or near Ha than nebulae or stars...

[AlexN]

Its worth noting, the smaller bandwidth filters will require longer exposure times... Shots taken with 2~4nm filters usually have TINY little pin prick stars, where as at 13Nm, stars almost appear as normal..

[winensky]

I use an Astronomik 13nm bandpass Ha and it provides quite natural star diameters, (due to the fact that it picks up a portion of the red end of the spectrum as well), very reasonable exposure times at f/4 and almost complete elimination of light polution/moon light. Also, 13nm filters tend to be less expensive. 4nm will remove more wavelenghts and so further reduce the effects of light pollution and non-systemic noise but at the price of requiring longer exposures. I have included a couple of examples of my Ha stacks I think about 1hr. and 30min.total respectively with my 13nm filter taken with fairly average gear. Hopefully, someone else could post a 4 nm. example.

Cheers.