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M42 Orion Nebula


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Hi all,

I had another shot at M42 on the 17th Jan. The moon was out in full glory so not ideal but given the beautiful British weather you need to take advantage of any opportunity!

Not a particularly long session with just 25 x 180s lights, darks, dark flats, flats and bias.

I had/have a couple of issues. The first I have seen before whereby the stacked image had a strange oliptical vignetting. I put that down to either lighting from the moon, overcorrecting flats or a bit of both?

Also and as you can see from the images below - most of the stars are slightly elongated but with a 'blip' favouring the bottom left of the star (the best I can describe it). What could be the cause of this? Equipment used is described below:

SW Esprit 100ED, ZWO2600 MC, evoguide 50ED, ZWO120 MM, on an AZ EQ6 all controlled by an ASIAir Pro.

I look forward to your comments and advise.





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Apologies, I said 'images' above and realised the second one didn't post.

Now added :) this is a close-up of the stars where the 'blip' described above can be seen in the larger stars. Could this be a spacing issue and/or tilt? Would this cause the stars to have the same issue across the entire image?

I can also see what I believe is pinched optics but will let others clarify that. It was around -2 and I've 'expected' this as I have heard many an issue with these scopes.

Anyhow, enough of my waffling...:)



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Further to the above (and i am not sure if this helps) but I ran the FWHMEccentricity script in PI on the original image (converted into Greyscale) and the following results emerged.

Admittedly I am a complete novice to this and I am not 100% what this tells me ☺️




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1 hour ago, CaptainKingsmill said:

I'm afraid I can't help you diagnose your problem but I just wanted to say that is a lovely image of M42 regardless :)


Thank you @CaptainKingsmill I am really pleased with it and it is a huge improvement over my last attempt.

Just a couple of issues to iron out and I am hoping someone can point me in the right direction!

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