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Old 04-03-2015, 08:20 AM
LewisM
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All Baader filters parfocal

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?
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Old 06-03-2015, 03:45 PM
LewisM
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Old 06-03-2015, 04:11 PM
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Peter Ward
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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.
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Old 06-03-2015, 05:41 PM
LewisM
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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....
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Old 06-03-2015, 10:11 PM
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Quote:
Originally Posted by LewisM View Post

Question - Did SBIG use UV/IR cut glass on the ST-2000XM chamber cover glass or chip slip glass?
No. A/R coated only.
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