Narrowband filter with a Newton F/4 ??

Hello,
I'd like to buy Ha and OIII narrowband filters because I live near a big town. The problem is that I have a skywatcher 200/800 F/4, and you know that big apertures and narrowbands are not friends… So my question is, if I have a F/4 telescope, will it works with a 6nm filter or I should use a 12nm ?
Thanks

Max Gillet:
you know that big apertures and narrowbands are not friends…

First time I hear this! Baader, Astronomik, Optolong make good NB filters. My suggestion is to search for your telescope in the AB search tool and pick up the narrowband images that you see. I noticed that you use a Canon 700d as camera, do you have also a monochrome camera or do you plan to buy one?

Hi Max,
F/4 is not very open, you could even use 3 nm but these filters are expensive and the gain is low. For optics with F/2.8 one needs to be more careful. Good NB filters around 5-6 nm are by far the best option for you. If you are in an urban area, I highly recommand not to buy 12 nm, you will get too much light pollution and as a consequence much lower contrast in your pictures.
Clear skies,
Andreas

Andrea Alessandrelli:
do you have also a monochrome camera or do you plan to buy one?

No it's for my Canon, I know it's not the best to use with narrowband filters but the monochrome camera will come later

Andreas Zeinert:
Hi Max,F/4 is not very open, you could even use 3 nm but these filters are expensive and the gain is low. For optics with F/2.8 one needs to be more careful. Good NB filters around 5-6 nm are by far the best option for you. If you are in an urban area, I highly recommand not to buy 12 nm, you will get too much light pollution and as a consequence much lower contrast in your pictures.
Clear skies,
Andreas

Ok that's perfect, I will buy a 6nm Ha and OIII filters. Thanks for the answer !

Last full moon I use a Castell UHC Filter: It let pass O-III and H-Alpha/S-II.

This was the result on my Lacerta modified 200/800 Newton (Newton ohne Namen). The mirror is the same from SkyWatcher.

https://astrob.in/403007/0/

Due a filtermismatch at full moon before … I used only a CLS + IDAS-D2 Filter at the same object:

https://astrob.in/397385/0/

The Sky background was heavy green :-) But this could be corrected while processing….

But narrowband on Bayer Matrix is hard…..

Siegfried

i would suggest the baader 4.5 nm filters..they are great ,dont have halos etc.
cheaper then Astrodon.

https://www.baader-planetarium.com/en/filters/deep-sky.html

As others have said, no problem with narrowband filters on a fast Newtonian telescope. I use 3nm and 5nm Astrodons all the way down to f/3.6 on a reduced FSQ106 with no ill effects.

I also use a 250mm f4 Newt with 3nm Astrodon Ha, O3, S2 & N2 filters with no problems

When I was talking to the guys at Chroma, they said that their 3 nm filters were good down to f/3.1. Below that, the angle of incidence becomes too steep and the center wavelength shifts. Anyway, I've been using 7 nm ZWO filters since January 2017 and recently got a 6.5 nm Ha from Optolong and a 3 nm OIII from Chroma. I've used all on my f/3.9 Newt with great results.

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