Whats your recommendation for a dual narrowband filter on a fast f/2 system?

Don’t have any experience, but there is a F2 Version of L-extreme filter:

https://optolong.com/cms/document/detail/id/276.html

Both the Antlia ALP-T HIGHSPEED and Optolong Lextreme HIGHSPEED filters can improve the transmission rate, but they still have a significant portion of the spectrum cut off.

The ALP-T 5nm high-speed has worked best for me. I also own the IDAS NBZ 12nm, but isn't as useful from B9 skies. If you can hold off on a purchase, Antlia mentioned that they are making a high-speed version of their new 3nm dual filter. Not sure how far away they are from releasing one, but I had asked about it last month when I saw the regular dual filter drop on Agena.

I have a bit of experience with this. I have a RASA, started with a 2600MC & dual band filter, moved to 2600MM & baader high speed filters.

For dual band filters, I've never been happy with the Optolong filters (L-Enhance, L-Extreme). They have tight bandpasses (especially L-Extreme & L-Ultimate), but the halos are brutal. My recommendation for anyone with a fast system is the IDAS NBZ. A slightly wider bandpass, but the quality of the stars and halos is top notch. No better filter for high speed systems in my mind.

For the mono camera, I use Baader Ultra-Highspeed filters. They are fantastic, and definitely the best ones that I can suggest for high speed systems when using mono. 

With regards to switching filters, I swap everything manually. It's pretty much impossible to add a filter wheel to a hyperstar / rasa, so you're stuck manually swapping. When shooting narrowband, it's a pretty trivial issues (I just shoot a single filter for each night). When shooting RGB, it's a big PITA. I definitely wish I had a OSC for shooting broadband.

Arny:

I decided to make a big investment and switch to a monochrome camera and use the Baader fast filters, and I never looked back.

Hi Rostokko,

that concern is exactly what worries me and going mono came to my mind as well - only that going mono would mean swapping filters by hand -- or living with loosing a lot of light collection area by cramping a filter wheel between camera and Hyperstar. 

Which route did you take - manual swap or filter wheel?

Arny

I do switch filters manually - I wouldn't even consider a filter wheel with hyperstar. I use the Starizona drawers, which are well made.
To be honest, it's not that big of a deal for me: I set things up to shoot, say, Ha for the night, and I create a plan which shifts through 2-3 targets - all of them in Ha; I would probably do that anyway to capture them where they are the high in the sky; being tied to a single filter per night just makes me wait longer to capture all the subs I need, but when I'm done, I have subs covering the 2-3 targets I chose.

smart strategy Rostokko - I will try that out!