Strange Flats with Antlia Pro 3 nm filters

[Thierry_Beauvilain]

Hello,

I got some strange circled patterns on preprocessed  pictures (with Siril 1.0.6).

When inspecting my flats I saw some vignetting and concentric circles and other strange things.

My setup is:

- Refractor APM LZOS 130 F6,

- APM Riccardi M82 Flattener (52 mm image circle) with M82 to M68 adaptor ring,

- M68 Zeiss rapid ring,

- M68 Baader tilt ring,

- QHY M OAG in M54,

- QHY CFW 3L 7 2'' filters with full set of Antlia Pro 2'' mounted with M48 threads LRGB + Ha OIII SII pro 3 nm

- QHY 600 M PH

- Home made flat box with ceiling light box with 224 led with white translucent polycarbonate + transluscent paper and white diffusing polycarbonate: much larger than the APM 130 aperture,

On luminance nothing appears and on others lots of things see attached pictures.

I compared with an Astronomik 2'' mounted filter in an Altair filetr box but with my previous camera a Canon EOS 6D MkII moded with astrodon filter and no rings on flats the sole vignetting is due to camera body.

Has anyone already got this with ANtlia filters  ?

What are your thoughts about that ?

 

Thanks a lot for your replies.

 

Clear Skies !

 

Thierry

[Elp]

I would say your flats are way too bright as I am currently going through a similar thing. I had to dim my led tracer panel to its lowest setting and use two 3mm opal acrylic sheets and one 3mm dark grey transparent acrylic sheet to dim down the amount of light significantly so I could take flats at 7.5 second duration through an lextreme filter.

[Oddsocks]

Hi Thierry..

The problem you describe is a known issue with the Riccardi Flattener, if you Google "Reflections with Riccardi Flattener" you will find many similar reports.

I understand that the problem is due to the curved concave shape of the rear element of the Riccardi, which reflects back to the sensor the rejected light from the skyward facing side of the filter.

The further the filter is from the Riccardi flattener the smaller the diameter and brighter that inner circle becomes.

You have proved that is the case with your luminance filter image, which naturally has a low back reflection and passes nearly all the light to the sensor, the RGB and narrow band filters will all have a higher level of rejected back reflection which is then returned again from the concave rear element of the Riccardi to the sensor, forming a smaller bright circle in the image.

You have also shown that placing the filter directly adjacent to the Riccardi results is no bright circular artefacts, which tends to support the theory.

The level of brightening will be influenced by the quality of the anti-reflection coatings of the filters, the distance the filters are from the flattener and the quality of the anti-reflection coatings on the rear element of the Riccardi.

To prove if the theory that the design of the Riccardi flattener is the underlying cause you can either take some flat images thorough an empty filter slot in the wheel, which should show either no circle, a much smaller circle, or a back reflection of the camera sensor, or, take the Riccardi flattener off the telescope and shoot some flats without the flattener, which should show no circular brightening with any of the filters.

I have no experience of Antila filters or how effective their anti-reflection coatings are but the quality of the filter coatings will be playing a part in this image quality problem.

HTH

Will.

[tooth_dr]

Very interesting that the Ricardi reducer is causing the issue.

I have an APM LZOS refractor and use the M63 version of the APM Riccardi reducer.  I used a smaller APS-C sensor and havent noticed these reflections in my flats.   I'm using 36mm Chroma NB filters.

 

[Oddsocks]

50 minutes ago, tooth_dr said:

Very interesting that the Ricardi reducer is causing the issue.

I have an APM LZOS refractor and use the M63 version of the APM Riccardi reducer.  I used a smaller APS-C sensor and havent noticed these reflections in my flats.   I'm using 36mm Chroma NB filters.

 

Your image field with the smaller APS-C sensor is probably lying entirely inside the brighter circle, so you would not necessarily be aware of the issue.

The diameter of the brighter circle is a function of distance between the filter, the Riccardi flattener and the sensor, which are all variables between one user and another and of course you are using well regarded Chroma filters, which along with Astrodon filters have top-grade anti-reflection coatings.

It's an interesting subject though and has been rumbling along for many years now.

Will.

[tooth_dr]

16 minutes ago, Oddsocks said:

Your image field with the smaller APS-C sensor is probably lying entirely inside the brighter circle, so you would not necessarily be aware of the issue.

The diameter of the brighter circle is a function of distance between the filter, the Riccardi flattener and the sensor, which are all variables between one user and another and of course you are using well regarded Chroma filters, which along with Astrodon filters have top-grade anti-reflection coatings.

It's an interesting subject though and has been rumbling along for many years now.

Will.

I’ve also a Baader 7nm filter in my wheel, I’ll try a flat with that later.

Baaders new reflex coated filters produced awful haloes with my setup, and swapping to Chroma solved it.  It seems the RIR may cause it, but it’s how the filters deal with it that varies a lot. 

[Starflyer]

19 hours ago, Thierry_Beauvilain said:

Hello,

I got some strange circled patterns on preprocessed  pictures (with Siril 1.0.6).

When inspecting my flats I saw some vignetting and concentric circles and other strange things.

My setup is:

- Refractor APM LZOS 130 F6,

- APM Riccardi M82 Flattener (52 mm image circle) with M82 to M68 adaptor ring,

- M68 Zeiss rapid ring,

- M68 Baader tilt ring,

- QHY M OAG in M54,

- QHY CFW 3L 7 2'' filters with full set of Antlia Pro 2'' mounted with M48 threads LRGB + Ha OIII SII pro 3 nm

- QHY 600 M PH

- Home made flat box with ceiling light box with 224 led with white translucent polycarbonate + transluscent paper and white diffusing polycarbonate: much larger than the APM 130 aperture,

On luminance nothing appears and on others lots of things see attached pictures.

I compared with an Astronomik 2'' mounted filter in an Altair filetr box but with my previous camera a Canon EOS 6D MkII moded with astrodon filter and no rings on flats the sole vignetting is due to camera body.

Has anyone already got this with ANtlia filters  ?

What are your thoughts about that ?

 

Thanks a lot for your replies.

 

Clear Skies !

 

Thierry

Sorry if I missed it somewhere in the thread, have you tried flipping the filters over?  When I was reading up on Chroma filters the manufacturer was adamant that filter orientation didn't matter, they're plenty of threads on CN that prove otherwise.

[tooth_dr]

On 08/11/2022 at 12:57, Oddsocks said:

Your image field with the smaller APS-C sensor is probably lying entirely inside the brighter circle, so you would not necessarily be aware of the issue.

I did rattle off a couple of flats using a 2" Baader 7nm Ha filter and the bright circle is definitely visible.  

[GTom]

I am not sure if we see vignetting or light reflection on your copy. There are no sharp edges like in the original post. Still, reflected light is a problem that needs to be mitigated to our best capacities. I wonder if using Baader's 3.5nm filter that I got would make any difference.

[Adam J]

On 30/07/2023 at 22:52, GTom said:

I am not sure if we see vignetting or light reflection on your copy. There are no sharp edges like in the original post. Still, reflected light is a problem that needs to be mitigated to our best capacities. I wonder if using Baader's 3.5nm filter that I got would make any difference.

just to be clear, are the flats not working? You don't explicitly say or show a stacked image.