Offset distance for Baader filters

[astrosathya]

Hello Everyone,

I have 7x 36mm Baader filters in my QHY Filter wheel. I use a simple Orion 80ED with a manual focuser. I have two questions basically.

a) How important is refocusing between the LRGB Ha OIII and SII filters? 

b) If important, then how do I manually calculate the offset distance between them assuming the filters aren't parfocal?

[david_taurus83]

They are supposed to be almost parfocal but I suppose the only way to be sure is to test each filter. I will be interested in this as I have ordered the very same set.

[astrosathya]

1 hour ago, david_taurus83 said:

They are supposed to be almost parfocal but I suppose the only way to be sure is to test each filter. I will be interested in this as I have ordered the very same set.

I've not had favourable weather to test all of them. I've used only the 7nm Ha filter and its brilliant. Light Pollution is a thing of the past when I use this filter. I hope to use all 7 this season.

[david_taurus83]

Yes the main reason I have decided to go mono and filters is the ability to image from my back garden. Need to travel to a dark site with my DSLR which I don't mind but the weather needs to be in agreement on a Friday or Saturday night and those nights are few and very far between!!

[astrosathya]

4 minutes ago, david_taurus83 said:

Yes the main reason I have decided to go mono and filters is the ability to image from my back garden. Need to travel to a dark site with my DSLR which I don't mind but the weather needs to be in agreement on a Friday or Saturday night and those nights are few and very far between!!

Precisely. I think all of us who reside in big Cities, be they London, NY, Tokyo, Bangalore etc., are best off with NB filters.