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Old 05-02-2021, 07:07 PM
Stefannebula (Stefan)
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Narrowband imaging with fast scopes

Hello all

I am imaging at F2.8 (SharpStar HNT 150 F.28) and I have just been using entry-level 7nm Optolong Ha, Sii and Oiii filters. I see some pretty nasty halos with these filters so I have been considering upgrading.

I have also been reading about the center wavelength shift that occurs at faster focal ratios, so I have been considering getting some 'fast' filters that are specifically tuned to account for this shift.

I know Baader has some high-speed filters but from what I've read they likely have a larger bandpass ~12nm. I am looking for something more in the range of 3-5nm. I know Chroma makes some, and Astronomik has a new series of fast narrowband filters but I haven't heard much about how either performs.

Does anyone here have experience with any of these 'fast' filters? Or could I get away with imaging at F2.8 with regular 5nm filters?

Thanks,
Stefan
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  #2  
Old 06-02-2021, 10:25 AM
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DiscoDuck (Paul)
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This from Astrodon may help.

In particular...
"This is not significant with our 5 nm
narrowband filters for most scopes slower than about f/3. The 3 nm filters may lose perhaps 20%T at f/3, but still useable."
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Old 06-02-2021, 08:31 PM
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multiweb (Marc)
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I have used a standard 7nm baader Ha with an hyperstar on my C11 and didn't have any issues with halos.
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Old 07-02-2021, 10:13 AM
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Peter Ward
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As mentioned above, AstroDon 5nm have no problems with fast optics.

I have been recently using both Baader and AstroDon filters, the Baaders do kick out halos on brighter stars.

The "dons" however, while not cheap, have been flawless.
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Old 07-02-2021, 11:02 AM
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gregbradley
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That has been my experience also. I have had Baaders before (not the latest gen though) and the green filter seemed the worst for halos.

I don't get halos from Astrodons except maybe under extreme scenes.

I image often at F3.8.

Greg.
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