What did I take a picture of?

[dutz]

I took a generic shot of the night sky on North Manitou Island. While playing with the raw image in Photoshop I noticed the rings, so I adjusted the hue and exposed the colored image. Can anyone tell me what that is?

[michael8554]

You haven't said what equipment you used to take the image.

The centre of most optical lenses/telescopes are brighter than the edges.

Not really noticeable on "holiday snaps", but when you stretch you exaggerate that difference.

And if the image is only say 8bit instead of 14 or 16bit, then stretching reveals those digital brightness steps.

Though you say you were processing a Raw, not a jpeg.

The answer is to take Flats and subtract those from the images in Stacking software.

Michael