Off-center halos around bright stars in FSQ-80FC images - Forums

Topic starter

8 hours ago

Any thoughts on what might be causing the off-center faint halo around bright stars? This is a single stretched frame with no calibration done to it only a simple adaptive stretch. The issue is clearly seen in the bright star in the right side of the frame where the halo is off-set away from the center of the frame. 📷 test.jpgThe particulars are:

Takahashi FSQ-80FC

PlayerOne Zeus mono

WandererAstro Snowflake filter wheel

Antlia new “Dark” series filters (50mm)

This issue shows up on all filters. The issue shows up on all bright stars and the off-set seems to be proportional to the distance away from frame center.

Any help greatly appreciated.

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andrea tasselli

Frequent contributor

7 hours ago

Your filters, most likely. Try without any filter.

Jeffery Richards

Topic starter

6 hours ago

Andrea, not disagreeing but don't straight filter halos typically show up centered around the bright stars? This is clearly skewed away from the center of the image frame.

A side note is that all of this equipment is brand new.

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andrea tasselli

Frequent contributor

6 hours ago

Depends were the reflection occurs. In refractors there is path length dependency on wavelength as well as (in doublets as well as in some of the triplets out there) magnification dependency on wavelength, hence the off center effect. Yours is a fast doublet, and as good as it might be, I guess it is to be expected for out-of-focus images. At any rate the test is simple to make, just remove one filter and see if the effect persists, hopefully not.

Jeffery Richards

Topic starter

5 hours ago

The new FSQ is actually a 5 element f5.6 double fluorite petzval design with a 50mm image circle.

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andrea tasselli

Frequent contributor

5 hours ago

It’s an air-spaced doublet with a 3-element field flattener, thus of a petzval design.

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Jeffery Richards

Topic starter

4 hours ago

I wonder if part of the issue is that these are the Antlia “Dark” series filters and I am currently using them in a Bortle 5 area (they will end up being used in Bortle 1).

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andrea tasselli

Frequent contributor

2 hours ago

That has nothing to do with propensity (or not) to generate halos. As yourself said, the halos are seen across all filters so it isn’t a matter of broader wavelength range (which would only apply to the R+ and the L filters, the other being “normal”). Personally I’d avoid straddling into IR territory with a refractor but that said, I shan’t think the issue is with your sky brightness.

Alex Nicholas

2 hours ago

It will 100% be your filters. They are off center based on how far off axis the star is in the image… if you put the star in the top left, the halo will be see off centered towards the top left of frame. If you put the star bang in the center, on axis, the halo will be centralised… you can prove it to yourself by measuring the halos size in pixels and calculating the distance from the sensor that the halo is… it will be on either your filters rear face, or on the internal corrector lens, reflecting off the filters front face.

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Jeffery Richards

Topic starter

1 hour ago

Thanks Alex/Andrea! I agree and have reached out to Antlia for their input. I’ve been pretty happy with the regular Pro filters on my iDK and when I go out to install the new FSQ, I may try swapping the filters between the two to see if I can live with things.

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