Mars Edge Rind Artefact Investigations

[Fossil Light]

Hi,

Imagers of Mars might be interested in reading the report on my investigations into the commonly seen 'edge-rind artefact' an example of which is shown below. The report is on my webite here;

Astronomy & Sky website of Martin Lewis - Mars Edge Artefact

It seems likely that the artefact is an optical diffraction effect and not caused by image processing or ringing in the camera or chip- although image processing will of course bring out the artefact.

There is a seeing dependence of the effect although it is not clear what the mechanism is here.

Comments welcome.

Martin

[Asimov]

Nice report, Martin. I read something similar some time ago with basically the same end conclusion(s). My simple method is just ignore it & after awhile I don't see it on images. No good worrying about something incurable.

[Fossil Light]

That's interesting, Asimov. Not convinced that nothing can be done about it though.

First step in looking for a cure is to understand the mechanisms. Investigations continue!

Martin

[Asimov]

No worries Martin. I do note it can have less of an impact in very good seeing but how often does that happen?! Oh I can cure it in software but more often than not I just ignore it.

[JamesF]

In your results table, are the theory headings around the right way? The conclusion you draw appears to me to be contrary to the results in the table. You say " the cause of the edge artefact seen on Mars is an optical diffraction effect" underneath the table, yet the column with no red entries in is headed "Chip related Signal Ringing at image sharp edge".

Excellent piece of work though. This is the first season I've done any imaging of Mars and this effect has been bugging me a fair bit.

James

[Fossil Light]

Well spotted, James. Table now corrected.

Martin

[neil phillips]

No worries Martin. I do note it can have less of an impact in very good seeing but how often does that happen?! Oh I can cure it in software but more often than not I just ignore it.

Exactly John, which is why im sure seeing also plays a big part in this. But there is something unusual going on, because some people have reported worse ringing in better seeing but not always ? Sometimes the opposite happens.

[Asimov]

I have taken particular note of this artifact this Mars apparition. In very good seeing it's very clear via the livefeed exactly what is going on & my conclusion was that it has nothing to do with how good or bad the seeing is, but the type of seeing. I've observed weird seeing just recently that I've never ever seen before.

I'm also starting to wonder if it couldn't be 'collimated out'. IE: Have Mars perfectly focused on-screen & tweek my SCT secondary screws to see any improvement (or worsening) of the limb artifact. I've done it once before on Jupiter, but for another reason entirely.

[Fossil Light]

I agree, Asimov, there seems to be some kinds of seeing which favour this artefact and in the UK there has been a lot of what ever it is this apparition. In 2010 I hardly had this artefact at all with almost the same imaging setup... maybe twice in 20 imaging sessions.

I wondered if the atmosphere was somehow mimicking spherical aberration which would throw much more light into the first ring of the airy disc. I will experiment with the program Aberrator which I am hoping will be able to simulate some of these effects on a dummy planet with different edge sharpnesses.

Please let me know if you do some collimation experiments and how you get on.

Martin

[Asimov]

Thanks Martin, & you can be certain I'll drop any further information in here regarding this. I'm actually looking at my best Mars AVI from this apparition so far; shot in ranging 8-10/10 seeing. It's only flaw is this darned artifact. Quite interesting to watch the video & I wish I had a good connection & bandwidth to be able to upload it..!!

I can only describe it as a vibration. The limb where the artifact presents itself is winking in & out of existence at a very rapid rate..Now if a stacking program could distinguish between this limb being there & NOT we might get somewhere..

[Fossil Light]

Hi Asimov,

That's what I did with my video that showed the same thing. It is detailed right at the end of the report under 'Solutions'. I searched through 3000 frames took out the 365 frames that showed the doubling but although those are definitely the badly affected frames (see processed comparison) taking them out made little difference to the avi. To me this says although the bad cases can be recognised removed it is there in embryonic form on probably all frames.

Martin

[Asimov]

Correct Martin & I can confirm that. I've done the same thing; hand stacked every frame without a noticeable artifact & still got the problem in the stack.

[Ringrocket]

Hello,

I don't know if it would be of any help in finding a reason for the dark artefact, but I stacked Venus in R6 which gave the usual mosaic allignment artefacts. I noticed that the darker edge rind artefact cuts straight through the mosaic borders.

Like the darker rind is produced after alligning etc ?

Jeffrey

[Fossil Light]

Hi jeffrey,

Not convinced that this implies the edge rind is produced after the alignment stage.

You should try decreasing the separation of your alignment points at the start to say 10 and see if that gets rid of the mosaic edges- you will break up the image into smaller chunks then.

Cheers,

martin

[Ringrocket]

Hi Martin,

Ok, so this is of no help than....

Thanks for the advice

However, I've already tried that and I get the same artefacts (so far in all avis I've tried to stack with it (Planets, Sun,Moon).

Actually I quit using R6 for stacking and went back to R5.

But at the moment I'm into getting to know that fantastic Autostakkert!2.

Cheers,

Jeffrey

[neil phillips]

Hi jeffrey,

Not convinced that this implies the edge rind is produced after the alignment stage.

You should try decreasing the separation of your alignment points at the start to say 10 and see if that gets rid of the mosaic edges- you will break up the image into smaller chunks then.

Cheers,

martin

I can see it live on screen coming and going, its happening at capture for sure

[Fossil Light]

Hi Neil,

I just added an except of the avi from which I derived the image at the begining of this thread, to the edge artefact article (Astronomy & Sky website of Martin Lewis - Mars Edge Artefact ). You'd best watch it full screen mode with scaling off. Is this edge flutter similar what you are seeing, Neil,

Martin

[Fossil Light]

FYI The avi is towards the end of the article under the section entitled 'Is the Edge Rind present in the Raw frames before any Processing?'

Cheers,

Martin

[todd8137]

not sure what you on about but thats one mega image of mars

[rawhead]

Thanks for your effort on this Martin.

Was driving me mad! Was convinced it was my scope or cam.

I now have to decide whether to leave it in the pics or 'paintshop' it out....

Hi,

Imagers of Mars might be interested in reading the report on my investigations into the commonly seen 'edge-rind artefact' an example of which is shown below. The report is on my webite here;

Astronomy & Sky website of Martin Lewis - Mars Edge Artefact

It seems likely that the artefact is an optical diffraction effect and not caused by image processing or ringing in the camera or chip- although image processing will of course bring out the artefact.

There is a seeing dependence of the effect although it is not clear what the mechanism is here.

Comments welcome.

Martin

[Ringrocket]

Could it be diffraction in the atmosphere of Mars as seen from the side ?

So the darker line is actually bordering the real edge of the MArs surface. I have seen an animation on a Dutch forum of someone who was fascinated by some clouds near the horizon that apeared to grow in the animation. There you can also see a small cloud that disappears over the horizon and crosses the dark rind and enters the white rind that could be the atmosphere ?

(I hope it's allowed to link to the thread)

Further down the page there's a bigger picture showing the small cloud upper-left)

http://www.astroforum.nl/showthread.php/139958-Mars-Wolkenvorming-deel-2!?p=484119#post484119

Jeffrey

[neil phillips]

Hi Neil,

I just added an except of the avi from which I derived the image at the begining of this thread, to the edge artefact article (Astronomy & Sky website of Martin Lewis - Mars Edge Artefact ). You'd best watch it full screen mode with scaling off. Is this edge flutter similar what you are seeing, Neil,

Martin

Hi Martin just saw your question, the compression on my dongle makes it hard to make out the video particulaly well. Though looking at your conclusions i belive your on the right track, as when i mentioned seeing causing this, I noticed edge flutter live on the screen that appeared to be the cause. The cure seems to be no edge flutter. But how to achieve that is the problem. What i take to be seeing related, could also be thermally related causing the edge flutter. But unless images taken with a thermally stable telescope produce no rind or edge flutter. Then we are back to seeing effects. Whatever this is, im convined its caused by the flutter you mention,

Though its curious when you tried to stack less fluttered images it seemed to make no difference which is odd ? I belive many frames with flutter must have been missed on that experiment. Havent read your intire report, in detail, have you tried stacking a small amount of frames starting at 50 or 100. hand picked with no flutter ?

Not sure any of this helping the discussion, just my thoughts. Images with no rind and the conditions at the time need to be studied further as a comparison