Focusing with SHO Filters

Acquisition Auto-Focusing Narrowband Deep Sky
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schmaks avatar
schmaks avatar
After my light with narrowband, I can tell that my focus is off.

When it comes to focusing, do you need to refocus with each filter separately?

I haven't yet received my EAF but am thinking it may be necessary to proceed with narrowband.

Thoughts?
Engaging
David Nozadze avatar
David Nozadze avatar
Hi Schmaks, 

I always refocus on each filter change. Even with parfocal filters and high end apochromatic scope, the focus point of various vawelengthes differ slightly. 

D
Concise
AstroDarkSky avatar
AstroDarkSky avatar
One thing to check on is if the software you use offers 'filter offsets'. With your EAF, you take focus point measurements in each filter as a base line ahead of time and then you just focus a single filter during image runs. Then the software moves the focus position for you during a filter change for you. So another auto focus run isnt needed just because you changed filters.

With NINA for example, you can you run a quick focus run with your Lum and focus offsets can be used to position the focus point -50 steps when it switches to Ha for example. There's a a plugin that calculates those offsets for you if you dont want to measure them manually.

Hope this helps! And yes, you can measure and see that parfocal filters are not exactly parfocal from the same company and some vendors are more precise than others with their specification.
Helpful
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