All Baader filters parfocal

[LewisM]

I have Baader LRGB and got in a Baader 7nM H-a the other day. The seating and height of the H-a in the carousel is significantly lower (cell height and depth) than the LRGB filters, and the substrate surface itself is a different distance "in" compared to the LRGB's.

Could this cause any parfocal issues, or just better to simply refocus H-a regardless?

[LewisM]

Silence is golden... I hear wind in the willows... :)

[Peter Ward]

Short Answer: re-focus

It should be the same thickness, but, with a convergent light cone, you will see a very slight shift in the focal point by moving a plano-optic closer to the objective.

Also, unless you have all-reflective optics or a superbly corrected refractor, the deep-red focus will very likely be different.

[LewisM]

Thanks Peter and understood. I previously always did refocus with Astronomik H-a, and they all seat the same and substrate distance same. Guess I will again.

Question - Did SBIG use UV/IR cut glass on the ST-2000XM chamber cover glass or chip slip glass? Just considering if I need to use s UV/IR in train with the CLS filter....

[Peter Ward]

No. A/R coated only.