Ghosting in Mars images

[Cosmic Geoff]

Many of my Mars images show a ghosting around the planet (see sample image).  This was taken with a CPC800, ASI224MC and x2 OMNI Barlow lens.

If I get a clear evening I can try narrowing down the cause before the Mars opposition & closest approach.

The problem is obvious only when using the Barlow lens, but it seems present in some non-Barlow images but much harder to see.  It is only obvious in processed images like this one, not in the live raw image.  I have imaged Mars both with & without an ADC and once or twice with a flip mirror assembly (i.e. no diagonal or Barlow or ADC in the light path), without nailing the problem.

I have swap outs for almost all the parts (including the telescope) but to pin down the problem could be time-consuming, so would appreciate a heads-up.

Edited September 30, 2020 by Cosmic Geoff

[vlaiv]

I think this is stacking issue - try changing alignment point size and see if it helps.

[Cosmic Geoff]

3 hours ago, vlaiv said:

I think this is stacking issue - try changing alignment point size and see if it helps.

That seems plausible.  I tried 11 alignpoints (instead of one) and it seemed to make the image more contrasty, but did not get rid of the ringing.   I discovered that Registax6 has a de-ringing function but it did not seem to do anything when I tried it.

[Nigella Bryant]

Is the telescope collimated ok. You need to be fairly spot on. 

[vlaiv]

6 minutes ago, Cosmic Geoff said:

That seems plausible.  I tried 11 alignpoints (instead of one) and it seemed to make the image more contrasty, but did not get rid of the ringing.   I discovered that Registax6 has a de-ringing function but it did not seem to do anything when I tried it.

Deringing feature is related to frequency restoration part. In process of restoring the frequencies, you can easily get ringing - which is "real" thing - but we don't like to see it in images.

Airy disk "rings" - here is image of airy disk produced by green laser:

Same thing that produces rings around airy disk is responsible for ringing that we sometimes get.

However, thing in your image is not ringing. Here is what ringing looks like:

If you are using AS!3 to stack your image - try using small alignment points, like 25px or smaller. This is what your Mars should look like under alignment points:

[markse68]

I think this is a very common problem- seen it in loads of mars pics. Sometimes mistaken for cloudy atmosphere. Not really noticed it on other planets. Is it something to do with the phase of the planet- it not being perfectly round? Or maybe the rotation of the planet shifting the details across the disk during multiple captures? 

Edited September 30, 2020 by markse68