Thanks Robert! To stretch just part of an image, in photoshop I just select that area using one of the selection tools, and then do new layer->curves, and adjust to taste. It creates a new layer with the brightness stretched just in that area.
and you're right about the brightness - for Mars I found best results were down under 150. It just goes to show that each planet requires her own special attention
Thanks Dave, but Bird's image is still far better than mine.
The crepe ring is the "innermost" ring, it's very faint and delicate, hard to capture and hard to keep during processing (aggressive processing can sometimes remove it).
See attached image with arrows.