Are all Baader 50mm unmounted filters parfocal?

[meade expert]

I am trying to find out if then entire Baader 50mm LRGB and Narrowband sets all parfocal with each other?
Does anyone know?:shrug:

[Tandum]

I'm heading in that direction and was assuming they are parfocal.
I'm pretty sure the newer ones are all 3mm thick and they are 50.4mm round.
I only have the NB set so far.

[meade expert]

I have a friend in the States that is using 50.4mm unmounted ones with 2 inch narrow band ones in the same sbig filterwheel and the 2 inch ones are slightly different focus.
I'm thinking of buying the 50mm ones but I need to know there isn't a focus issue between narrowband and normal LRGB?

[Peter.M]

I am 90% sure that narrowband filters will always have slightly different focal points regardless of brand. I have a set of the baader narrowband filters and I would not focus with one and use the other. I dont find this to be too restricting though because for narrowband images you need to aquire alot of subframes to decrease noise so getting all of them in one night is impossible.

[Tandum]

I had a full set of 36mm Baaders in a 7 filter SX carousel a while back and they where mostly parfocal. By that I mean some scopes didn't see them as parfocal (some refractors) but others did (all reflectors). I definately wouldn't mix mouinted and unmounted or different sized filters and expect them to be parfocal.

[RickS]

Parfocal is a vague term. I have a set of "parfocal" Astrodon LRGB filters. They all focus at slightly different distances and on my Tak FSQ-106ED at f/5 they are not parfocal. The maximum difference in focal distance is between red and blue at just under 90 microns compared to a CFZ of 55 microns. On my GSO RC10 at f/8 (with a much more generous CFZ of 140 microns) they are fine.

So, YMMV, especially with faster scopes.

Cheers,
Rick.

[Peter Ward]

Par focal really only means "same thickness". While Baaders are indeed the same thickness spec. , you will however find there are small batch variations from one production run to another.

Convergent light cones (i.e fast optics) exaggerate filter thickness variations.

If you are using a refractor, spherochromatism will show focal differences from the Red through Blue of the spectrum.

The degree to which your objective is corrected will hence determine whether or not you still need to re-focus.