Canon 200mm f/2.8 with Optolong dual band filters causing strong image gradients

Optolong L-Ultimate filter 11 replies127 views
Carlos Rincón avatar

Hi everyone,

I’ve been experimenting with a Canon 200mm f/2.8 lens combined with the Optolong L-Ultimate filter, and I’m consistently getting strong gradients across the image. From what I’ve read, this may be related to a kind of shift banding effect caused by the interaction between the filter and the fast lens.

The same thing also happens with the Optolong L-eXtreme, although in a less pronounced way.

Has anyone experienced this issue? Do you know if there is a reliable way to eliminate or at least mitigate these gradients during capture?

Thanks a lot in advance for any advice!

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bigCatAstro avatar

Does the gradient still happen if you stop down the lens and what image editing software are you using to remove gradients?

Brian Puhl avatar

Please give us a screenshot of what’s going on.

Being a wider field of view, I’d more likely believe this is a external gradient caused by light pollution.

andrea tasselli avatar
If it is really Stokes shifting there is nothing you can do about it. This said, L-Extreme and even more so L-Extreme do NOT work well with fast systems.

This said, if you can live with a stopped down aperture you can place the filter ahead of the lens proper, via step-down rings.
Mikołaj Wadowski avatar

Are the gradients visible in your master flat? If so, are they visible after flat calibration?

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Carlos Rincón avatar

bigCatAstro · Sep 21, 2025 at 05:29 PM

Does the gradient still happen if you stop down the lens and what image editing software are you using to remove gradients?

Many thanks for your feedback. I´m shooting @f:4 and the gradents are still there. I normally remove the gradients with MGC and it works quite well normally except in the corners where I have to crop the image a litltle bit.

Carlos Rincón avatar

Mikołaj Wadowski · Sep 21, 2025 at 09:49 PM

Are the gradients visible in your master flat? If so, are they visible after flat calibration?

Many thanks Mikolaj. Yes, they are but after calibration the gradient are still there, Not no strain biut still there. This is not the case when I shoot with the same filter and the RC8”. The filter causes gradients and they are vanished after calibration.

Carlos Rincón avatar

andrea tasselli · Sep 21, 2025 at 05:59 PM

If it is really Stokes shifting there is nothing you can do about it. This said, L-Extreme and even more so L-Extreme do NOT work well with fast systems.

This said, if you can live with a stopped down aperture you can place the filter ahead of the lens proper, via step-down rings.

Many thanks Andrew, I think this is a fantastic idea. Probably with the filter in front of he lens the effect will disappear. And actually I will not loose that much luminosity. The 2” filter is 50,8mm so in a 200mm lest it will stop down from f:2,8 to f:4 which actually is the f stop I´m actually using. Great idea!

Carlos Rincón avatar

Brian Puhl · Sep 21, 2025 at 05:32 PM

Please give us a screenshot of what’s going on.

Being a wider field of view, I’d more likely believe this is a external gradient caused by light pollution.

Hi Brian, many thanks for your feedback. I would say is not light pollution. I use the lens with less restrictive filters (Optolong L pro) and the light pollution gradients are completely different and not so strong. The gradient caused by the filter is green/red so that’s why i believe is caused by a band shift effect. Attached a screenshot of a masterligth w/o any processing and after removing gradients with MGC and processed in PixIsight.

📷 Velos_Xtreme_V6_mas_reduccion_estrellas.jpgVelos_Xtreme_V6_mas_reduccion_estrellas.jpg📷 Captura de pantalla 2025-09-22 a las 7.51.55.png. Captura de pantalla 2025-09-22 a las 7.51.55.png

andrea tasselli avatar
We all get it.
bigCatAstro avatar

Carlos Rincón · Sep 22, 2025, 05:44 AM

bigCatAstro · Sep 21, 2025 at 05:29 PM

Does the gradient still happen if you stop down the lens and what image editing software are you using to remove gradients?

Many thanks for your feedback. I´m shooting @f:4 and the gradents are still there. I normally remove the gradients with MGC and it works quite well normally except in the corners where I have to crop the image a litltle bit.

I would try using the GraXpert process module in Pixinsight and see what you get after a background extraction. At least do a comparison between processes and see if your results are different.

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Carlos Rincón avatar

bigCatAstro · Sep 22, 2025 at 12:58 PM

Carlos Rincón · Sep 22, 2025, 05:44 AM

bigCatAstro · Sep 21, 2025 at 05:29 PM

Does the gradient still happen if you stop down the lens and what image editing software are you using to remove gradients?

Many thanks for your feedback. I´m shooting @f:4 and the gradents are still there. I normally remove the gradients with MGC and it works quite well normally except in the corners where I have to crop the image a litltle bit.

I would try using the GraXpert process module in Pixinsight and see what you get after a background extraction. At least do a comparison between processes and see if your results are different.

I´ll try it. Many thanks