I'm a fairly newbie in astronomy. I'm just starting to be able to find some deep sky objects using the star hopping technique. But I live in a contamited area (should be suburban but it's very near Madrid) and faint objects are really hard to see. The only nebulas I've been able to observe are the Orion Nebula, a bit of the Lagoon Nebula and the Ring nebula.
Looking for a filter, I found one in AliExpress that it's supposed to pass H-Beta and both lines of O-III. It's not a UHC filter since it does not pass the red wavelenghts. It's sold as an H-Beta filter but with a 25 nm passband it also passes O-III. Supposing it meets its specs, do you think it would be a good filter? It's somehow similar to Orion Ultrablock.
I've attached the transmission diagram.
My scope is a 6 f/8 dobson.
Thanks in advance.
Edited by ivazquez, 24 September 2020 - 05:46 AM.