Which filter for osc

[xelasnave]

I thought there was a thread but I can see it and the search feature does not work for me.
I have a ZWO 2600 which will live on my 80 mm Espirit and I am thinking about a dual filter or tri filter of some kind ...however these filters it seems are for light polluted regions and I am in a reasonably dark site...is there any point in getting a filter and if so what one?
It seems to me that such filters brings you c1lose to the benefits of narrow band imaging which appeals...any advice gratefully received.
Alex

[Startrek]

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

[Nikolas]

There is the Optolong L-Extreme and the Antlia duo Gold both are excellent filters.

[JA]

Hi Alex,

Your sky is incredibly dark: Bortle 1 SQM 21.99 !!!! (based on the stated Tabulam location in Lightpollution Map World Atlas 2015 -see below), you don't need any light pollution filters, unless of course you specifically want to do narrowband imaging with your 2600MC OSC colour camera and some dual/tri band filters and split off the channels, but don't you also have a 2600mm that you could use if you wanted to narrowband image?

Best
JA

[The_bluester]

Alex, for full OSC, in your dark skies I would not worry about a filter, the window on those cams is equivalent to a lum filter to begin with (Something that they learned from reflection issues with the ASI294 which was not a full UV-IR cut wideband window) If you want to do NB with it, you can do with actual NB filters and while I cant comment on any other programs, Astro Pixel Processor has debayer algos to extract HA or Oiii or Sii from OSC images shot with NB filters. It also has algos for multi band filters but I have never played with them as I don't have the filter.

NB with the OSC is not as effective as NB with a mono cam, but it is a pretty good second in my experience.

[xelasnave]

Thanks for all your wonderful replies.
I looked and the filter I would get was $600 and there are only 15 left in stock so I felt pressured to act.
I was thinking about the narrow band aspect but I have concluded from all the advice such that I wont buy one l at this stage.
Thanks all your replies helped me greatly I can assure you.
Alex

[M_Lewis]

there are plenty of options out there for decent NB (dual) filters for an OSC. I personally use the IDAS NBZ (so you do not get halo's), and sometimes use the L-Optolong Extreme when I'm imaging certain targets as it has a narrower bandpass as compared to the IDAS. The L-Extreme will give halo's on very bright stars.... (just saying). I use the 2600 OSC, and the dualband nb filters, and also add in a Sii filter on some targets. Some may call that crazy, however after 12 years of doing this hobby, I enjoy making an OSC perform as good as a mono, as there is a dark art in post processing photons.

I would also suggest it is definitely worth exploring, have a look a cuev the lazy geek's channel on youtube. Personally I would stay away from any of the tri-band or quad band filters using an OSC, why - well it's a waste of money on the tri-band (it's not Sii/Oiii/Ha - it's Hb,Ha,Oiii) and quad bandpass filters tend to cause a few issues on OSC sensors.

If i had to recommend one above the rest - IDAS, wins hands down.

[evltoy]

I heard the same thing recently from the fella "The Narrowband channel" he save me a few $$$ :)

[JohnH]

Is here:


https://www.researchgate.net/publication/344786226_Multi-Narrowband_Astronomical_Filters


Well, probably....might be a bit out of date....