Looking for Advice on SII & OIII Filters - Halo Issues with Askar D2

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Menelaos avatar
Hi everyone! I need some advice on narrowband filters. I currently own the Askar D1 and D2 filters. The D1 is fantastic great colors and truly halo-free. However, while the D2 produces nice images, I’ve been struggling with halos, which is quite frustrating. Askar advertises these filters as halo-free, and considering their price point, I expected better performance. I initially opted for the more expensive range, assuming it would guarantee better quality. While researching alternatives, I came across the Altair filters. They are more budget-friendly but also claim to be halo-free. Does anyone here have experience with them? I am specifically looking for SII - OIII dual band filters. Any recommendations would be greatly appreciated!
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andrea tasselli avatar
Which ones, the 4nm or the 6nm ones? And at what focal ratio? They have been tested (and the test has been reported in AB a couple of months ago) and results seem quite positive. As far as I can recall the OIII+SII filters were found halo-free (if the terms is applied correctly).
Menelaos avatar
andrea tasselli:
Which ones, the 4nm or the 6nm ones? And at what focal ratio? They have been tested (and the test has been reported in AB a couple of months ago) and results seem quite positive. As far as I can recall the OIII+SII filters were found halo-free (if the terms is applied correctly).

I would go for the 6nm since i’m looking something equivalent for the Askar D2
andrea tasselli avatar
And what about speed of the scope?
Menelaos avatar
andrea tasselli:
And what about speed of the scope?

F 5
andrea tasselli avatar
Seems well within the margins. I'd recommend going for the 6nm one, hopefully they are available (the OIII-Ha isn't).
Richard Carande avatar
I have the D2, and there are no noticeable halos with mine except on the brightest stars, and in Oiii only.  It's much better than the Oiii halos from the L-eXtreme I have.  Maybe you can exchange the filter if you give the vendor a call.  I have been happy with the D2.
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danieldh206 avatar
Astronomik filters from Germany are worth looking at. https://www.astronomik.com/
High quality and fast shipping, and not expensive like Chroma.
Michael Jarvis avatar
I own the Askar D2 and have had good imaging with it.  I have generated several images using the D2 coupled with the Optolong L-extreme filter.  Image train consists of RedCat 51 and ASI 2600 MC Pro.  Integration times vary 10-20 hrs for emission nebulae.  There are some image-dependent halos but these are relatively easy to deal with using Pixinsight (invert/SCNR process).   Check out Cuiv's or Tony de Nardo's YT workflow videos.  Hope this helps.
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John Wells avatar
Thank you for posting this topic as I've been holding out on the Askar D2 due to the cost, and only just came across the Altair 6nm as an option.

It has been hard to find any useful review of it… I assume it is a rebranded filter from somewhere but hard to figure out where.
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andrea tasselli avatar
John Wells:
Thank you for posting this topic as I've been holding out on the Askar D2 due to the cost, and only just came across the Altair 6nm as an option.

It has been hard to find any useful review of it... I assume it is a rebranded filter from somewhere but hard to figure out where.

It's not a rebrand.
2024-09-10_Dual-Band_Filter_Comparison_FBrill_official.pdf
John Wells avatar
andrea tasselli:
John Wells:
Thank you for posting this topic as I've been holding out on the Askar D2 due to the cost, and only just came across the Altair 6nm as an option.

It has been hard to find any useful review of it... I assume it is a rebranded filter from somewhere but hard to figure out where.

It's not a rebrand.
2024-09-10_Dual-Band_Filter_Comparison_FBrill_official.pdf

I couldn't have asked for a more comprehensive review, thank you!
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David Néel avatar
Got the two altair 4nm (Ha OIII and SII OIII). No halo.
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