Dealing with huge vignetting

[Blanconuclear]

Hello everyone,

In my fourth astrophotography session with my new Takahashi FSQ85 telescope, I decided to take 300s exposures of the Markarian Chain. For my previous photos of emission nebulae, I have always used narrowband filters (L-eNhance and IDAS NBZ) with my QHY 294PROC and obtained good results. However, this time I decided to remove the filter from the filter tray and leave it empty to prevent the entry of parasitic lights, as I have done before with my previous TS80Q telescope. I took 57 exposures of 300s.

The result was an exaggerated central vignette that could not be eliminated with flats. This is due to the missing filter in the filter tray, combined with the focal length of the BabyQ with the coupled reducer. The session data are:

• Takahashi FSQ85 EDX
• QE Reducer 0.73x
• Baader Planetarium UFC 2" empty filter holder
• QHYCCD 294PROC
• 57 x 300s lights
• 20 flats
• Darks + bias

I have tried to remove the vignette using DBE in PixInsight, GraXpert, and Photoshop (with the stretched image using STF), but I cannot completely remove it without losing a lot of the original signal. Ideally, I would like to remove it before stretching the image in PixInsight. I am considering discarding the data and trying again in a future session. Do you know of any way to remove it without losing signal?

Thank you and clear skies,
Francis.

 

[cloudbait]

Hello everyone,

In my fourth astrophotography session with my new Takahashi FSQ85 telescope, I decided to take 300s exposures of the Markarian Chain. For my previous photos of emission nebulae, I have always used narrowband filters (L-eNhance and IDAS NBZ) with my QHY 294PROC and obtained good results. However, this time I decided to remove the filter from the filter tray and leave it empty to prevent the entry of parasitic lights, as I have done before with my previous TS80Q telescope. I took 57 exposures of 300s.

The result was an exaggerated central vignette that could not be eliminated with flats. This is due to the missing filter in the filter tray, combined with the focal length of the BabyQ with the coupled reducer. The session data are:

• Takahashi FSQ85 EDX
• QE Reducer 0.73x
• Baader Planetarium UFC 2" empty filter holder
• QHYCCD 294PROC
• 57 x 300s lights
• 20 flats
• Darks + bias

I have tried to remove the vignette using DBE in PixInsight, GraXpert, and Photoshop (with the stretched image using STF), but I cannot completely remove it without losing a lot of the original signal. Ideally, I would like to remove it before stretching the image in PixInsight. I am considering discarding the data and trying again in a future session. Do you know of any way to remove it without losing signal?

View attachment 18421

Thank you and clear skies,
Francis.

I don't think that's classical vignetting, which should fall off geometrically. It's more like a shadow phenomenon.

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[Blanconuclear]

Thank you for the quick response.
I do indeed see the reasoning behind your suggestion, and I will need to dedicate some time to apply it. I see that I may have issues with M86 since it is located right on the edge of the circle. I will need to modify the circular mask so that it does not affect it.