ha veiwing filter ??

[astrokat]

can you get a filter that enables you to look at nebula thats mostly ha eg ic 1805 heart neb

thanks toby

[Space Bat]

There woudn't be a point as you can not see Ha at night - due to the eyes sensitivity dropping off when your eye is dark adapted.

Sensitivity of our eyes at night with Ha at 656nm is recognised to be 0%

Chris

[brianb]

Hydrogen nebulae which emit Ha will emit hydrogen beta too. Hb is in the blue/green part of the spectrum, right at the peak of the dark adapted eye. Hb deep sky filters are widely available ... though I must say that they are not that useful, mostly because nebulae which shine by hydrogen emission only tend to be rather faint, and a dark sky is far more helpful than a narrowband filter for viewing them.

In any case an ordinary didymium / CLS type anti-pollution filter will pass hydrogen beta and remove most of the skyglow.

[astrokat]

thanks guys