This may or may not help but here are some things on filters. On the Lumicon site it's useful to see that there are exit pupils which suit each filter. I started out with 1.25" Baader filters (UHC and O-III) but it wasn't long before I had a few 2" eyepieces in which these filters are useless. The 2" eyepieces were at longer focal lengths (bigger exit pupil) where the extra barrel size is needed and this is also where the filters were actually more useful. So, if you have some kind of adapter or extension tube in which the 1.25" eyepieces sit that has 2" filter threads I'd say buy the 2" version of the filter to future proof a bit. That's my experience anyway. I use the Astronomik 2" UHC filter and love it, especially in light polluted skies.
http://www.lumicon.com/store/pg/15-L...a-Filters.aspx
A test to see if what Lumicon say is true...
http://www.lcas-astronomy.org/articl...gory=eyepieces
Filters and the targets they help with...
https://www.cloudynights.com/article...parisons-r1471