Good grief, Paul! That's no onion ring! It's a fried egg!
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how are said onion rings created?
you slice but don't dice! Process and process some more. I suspect it's a "ringing" effect that is a side-effect of many "sharpening" type image processing operations near hard edges.
There are a few theories on how they are created. I think unstable seeing conditions have a lot to do with it, where the planet pulsates in and out. You will only notice it at high magnification, that is the pulsating. Onion rings are not viewed throuth the eyepiece, but captured with a web cam, where the images are stacked to make one image.
There was a rather good discussion a long time ago about the rings and from what I rmember bird came up with the best explaination. If I remember corrrectly it had to do with registax inability to deal with the gradual darkening towards the limb in under exposed shots, which is why applying gain and gamma is suggested so strongly.
I think that was it. Someone might want to do a search for it, but it was wayyy back when.
I think your probably right Lester. That's what I guessed it at anyway. This was probably only the 2nd or 3rd Jupiter I ever took way back in the early years. You know around March last year
Are you sure it's not a 240V voltage drop, caused by too many people using aircon or heater power, that can affect just about everything.
I have seen you guy's using 240 leads to your equipment.
Onion rings are the bane of my life. I've fiddled with just about every setting imaginable to deal with them, but it's become clear to me that it's not a simple single variable like under-exposure that's to blame. I've had way under-exposed shots with no rings, and burnt out over-exposed with rings so bad you could crumb and deep fry 'em and sell 'em at Hungry Jacks!
That said, under-exposure IS definitely a factor. Seeing and planet disc stability is also without any doubt in my mind another. Gamma doesn't seem to have much impact, but Gain does. My best success in reducing the incidence and severity of Onion rings has been by decreasing exposure time (I used to image at 1/10th -1/20th sec, no at 1/25th to 1/33rd) and upping the gain to suit. Still keeping actual exposure around the same in the low 200's on the K3CCD light meter.
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Process and process some more. I suspect it's a "ringing" effect that is a side-effect of many "sharpening" type image processing operations near hard edges.
