H-Alpha filter and the moon

[gorann]

What I (and probably others) would like to know is if a 3nm Astrodon beats a slightly cheaper 3 nm Chroma, or a much cheaper a 3.5 nm Baader, and a much much cheaper 7 nm Baader (and what about the 6nm Astronomik)?

In short, should I just be happy with my 7nm Baader?

[wimvb]

1 hour ago, gorann said:

What I (and probably others) would like to know is if a 3nm Astrodon beats a slightly cheaper 3 nm Chroma, or a much cheaper a 3.5 nm Baader, and a much much cheaper 7 nm Baader (and what about the 6nm Astronomik)?

In short, should I just be happy with my 7nm Baader?

Wider filters let more light pollution through, which ends up filling the pixel wells, and adding noise. Narrower is better. But as a manufacturer, you have much more relaxed production specs for 7 nm filters. Afterall, at 7 nm it will be easier to hit the (Ha) emission line, which is much narrower than the filter passband width.

Besides passband width, the glass needs to be of excellent quality, and the filter needs to have good AR coating on both sides. Finally, the specs need to be met even for low f-ratios. (Light will not enter the filter at only right angles.) Overall filter quality is not only determined by line width.

[gorann]

It may be that Chroma stopped producing 3nm Ha filters since I can only find 8 nm Ha filters on their web site and OPT appear to have run out of them. Could be that they are just so difficult to produce (as you say @wimvb ) that it is not worth while commercially, but it would be a pity since I read somewhere that Sara rated them as high as Astrodon.

[ollypenrice]

10 hours ago, gorann said:

What I (and probably others) would like to know is if a 3nm Astrodon beats a slightly cheaper 3 nm Chroma, or a much cheaper a 3.5 nm Baader, and a much much cheaper 7 nm Baader (and what about the 6nm Astronomik)?

In short, should I just be happy with my 7nm Baader?

Goran, I'm glad you posted this because I didn't know Baader had introduced this one. I can see myself giving it a try! I must now try to find if they are doing a tighter bandpass OIII filter as has been rumoured for some time.

Thanks for the heads up!

Olly

[gorann]

Now when you asked Olly, I had a look at the Baader Planetarium site and they only list Oiii 8.5 nm right now (but maybe the site is not updated or maybe you could be a beta tester?). OPT lists 3 and 5 nm Chroma Oiii filtes that are considerably cheaper than Astrodon, but still pricey and they all seem to be on back order which may be a bad sign.

By the way Olly, do you have any experience regarding the performance of the Baader 3.5 nm Ha compared to Astrodon 3 nm Ha and Baader 7 nm?