[Startrek (Martin)]

Alex,
I use my 2600MC with the Optolong L Extreme filter under Bortle 8 Sydney and Bortle 3 South Coast both under full moon and new moon with excellent results on specific emission nebula.
These filters are not dedicated light pollution filters but narrowband filters with a specific bandpass on Ha and Oiii wavelengths namely 7nm. So under heavy LP and moon glare you still have gradients to deal with
In Sydney I still have to deal with LP and Moon glare gradients using the L Extreme but at least the signal is there , you just have to mitigate the noise in post processing and the emission detail is definitely there.
Down south obviously the gradients are no where near as severe using the filter under the moon and the results are excellent.
During the new moon down south ( Bortle 3 ) the filter works brilliant especially for OSC narrowband images on objects like Lagoon, M17, M16 , Prawn , Lobster nebulas and many others ( some objects emit more Oiii and Sii than others but most have strong Ha ) The L Extreme doesn’t work that well on reflection nebula like M20 and others and was never designed for galaxies or clusters etc….
Splitting the channels to produce a bonafide Narrowband image is difficult but can be done with a OSC. I use Compose in Startools with some success, although some folk on the forum are producing excellent NB results from Pi and PS
I started using the ZWO Duoband ( 21nm and 13nm ) with good results and then moved on to the L Extreme ( 7nm ) which produced far better results. I believe the Antlia “Golden Filter” is the latest product for OSC narrowband at 5mn bandpass on Ha and Oiii
Optolong were supposed to manufacture a 3mn filter called L Ultimate but it’s yet to hit the market.
I’m not sure but I think Antlia make a OSC narrowband filter for scopes with focal ratios as low as f2 , maybe have a look ?
The only downside to these OSC Narrowband filters is some folk experience large halos around the brighter stars ( refractors and the like ) and the filter does affect Star colour which can be dealt with using a good Star mask in post processing. Other than that they are a really great accessory and are improving all the time.
I might progress to the Antlia next year or the L Ultimate if it ever eventuates.

Cheers
Martin