What's this circular artefact on my image?

[LaurenceT]

I had a very quick go at M42 the other night before it dived into the trees, just 14 x 60 seconds integration time. I noticed this large circular artefact in the image and it also appeared om my Bodes image later that night. Any ideas what it's due to?

Edit: my wife took one look at it and said it looks like dust. A quick Google shows that it probably is dust. I'll run my setup past her first next time.

Edited February 20 by LaurenceT

[Elp]

Likely out of focus dust somewhere in your image train. It's one of the reasons flat frames are applied when doing AP.

[ONIKKINEN]

Yup, a shadow from a mote of dust. Most likely on the sensor window, or if you have a filter somewhere close to the sensor then on that.

Flats are the cure.

[TiffsAndAstro]

Lovely image btw. Flats and/or a clean should do.

[LaurenceT]

On 24/03/2024 at 15:47, TiffsAndAstro said:

Lovely image btw. Flats and/or a clean should do.

Thanks, I've just started taking flats and dark flats now, it's made a difference.