benefits of a ha filter

[iwols]

hi all just,mainly into dso and using an ed80 ,atik 414ccd and lrgb filters on a heq5 pro mount,and just wondered what the benefits of an ha filter would bring,flo do a ha 7nm and 35nm,which of  these two would be a good start on there own or do i need the hb,oiii and sii as well any explanations appreciated thanks

[ollypenrice]

A great many of the best targets for your focal length and chip size will be emission nebulae, most of which radiate strongly in the H alpha line. A normal red filter passes all the Ha signal but what the Ha filter does is block everything except light given off by the glowing hydrogen. This allows us to see its structure very plainly, with lots of contrast. This can be used to make a monochrome image...

 

or we can add the Ha to the red channel to enhance an LRGB...

In some extreme cases almost all of the interest comes from the added Ha layer.

OIII can be used in a similar way added to blue and green but Ha is more productive by far. Another Ha advantage is that it is relatively, but not totally, moon-proof. The narrower the bandpass the better, so go for 7nm as a maximum bandpass. I also have a 3nm and greatly prefer it, especially in the moon.

Finally you can make false colour images using other narrowband filters. This is very useful in the fight against light pollution if you have it.

Olly

Edit. Recently I've found that only the first of my Smugmug links appears on here as an image. Does anyone know why that is?

[Knight of Clear Skies]

Another benefit of an Ha filter is that it can help isolate faint nebulosity from a dense starfield. For example, here's a wide shot of Cygnus:

Without the filter some of the faint structures would have been lost against the mass of stars. With Ha filters the narrower the passband the better. Mine is 12nm, a narrower one would have suppressed the stars even more.

[ollypenrice]

18 minutes ago, Knight of Clear Skies said:

Another benefit of an Ha filter is that it can help isolate faint nebulosity from a dense starfield. For example, here's a wide shot of Cygnus:

Without the filter some of the faint structures would have been lost against the mass of stars. With Ha filters the narrower the passband the better. Mine is 12nm, a narrower one would have suppressed the stars even more.

Excellent point. Narrowband stars are deliciously tiny, which is a huge benefit in widefield imaging within the Milky Way. The 3nm Ha stars are incredibly tiny but this does mean that sometimes you have to slew to a bright star to focus or refocus.

Olly

[iwols]

thanks guys looks like 7nm is a happy medium cheers