Image problem with stepped vignette.

[Spacehead]

Hi All,

I've been stacking images and found i'm getting these stepped rings in my DSS stacked file.
I get it whether I stack the jpgs or the cr2's from my canon eos1300d.

The following four images are stacked results of the horsehead, with no flats and no darks (i've messed with them to enhance the rings for you to see).
top left is jpegs, lights stacking mode - average
bottom left is cr2s, lights stacking mode - average
top right is jpegs, lights stacking mode - auto adaptive weighted average (seems to get rid of the rings)
bottom right is cr2s, lights stacking mode - auto adaptive weighted average (just makes a mess really) 

I am trying to avoid having to buy a new camera, as I haven't used this one much and I know that £400 isn't loads of money to many folk - but its a shed load to me.

Other info, the rings ARE present in the actual individual subs (BOTH jpg AND cr2) - see the second image (samplight.jpg).
I took some flats for this dataset, and the rings are also present in the flats - as seen in picture 3 - (sampflat.jpg).

The lights are 1min, iso 400

The rings are present even when I take an image of the floor - with no camera lens on - just the camera on its own, no scope or anything.

Naturally, the rings are being stacked - but as I understand it - just stacking the set alone should provide a smooth gradient going darker to the edges - not this stepped ring business I am getting.

So I am assuming that because the rings are present from the word go - in the cr2s, then the problem isnt the stacking - its the camera.

Can anyone advise?

Depressed here.



 

[michael8554]

Well as nobody else has replied, I'll give it a go.

Most of your images seem to be screen grabs which could have all sorts of artefacts - could you post the saved images as higher res jpgs,  say  a single sub and a single flat ?

Michael 

[michael8554]

I've just seen serbiadarksky's image - wierd coincidence !

Michael 

[Spacehead]

On 28/02/2019 at 22:18, michael8554 said:

Well as nobody else has replied, I'll give it a go.

Most of your images seem to be screen grabs which could have all sorts of artefacts - could you post the saved images as higher res jpgs,  say  a single sub and a single flat ?

Michael 

Michael - thanks for replying - sorry about the delay getting back on here.

Here is a flat and a light actual files, and my screen shots of them with lowered contrast to show the rings.

I'm not worried whether the pics are good or bad in any aspect other than the rings.  They are worrying me.

If you have anything at all which may help me out here i'd be really grateful.
Cheers
 

IMG_8267.CR2 IMG_8246.CR2

[michael8554]

I can't view Raw's on my tablet, which is why I requested you post some JPEG's   ?

So I fired up my PC and twice applied a heavy gamma stretch (300arcsinH) to your Light and Flat .

This is far more than I would ever apply to my images without showing unacceptable noise.

Slight rings on the Flat, hardly visible on the Light.

I've also done the same stretch to one of my Canon 6D Flats, almost invisible rings.

These rings are the sample levels of the digital image becoming visible due to the extreme stretch applied.

First thought is that the DIGIC 5+ processing of the 6D is better than the DIGIC 4 of your 1200D.

But IMO your images aren't showing any artefacts that aren't apparent in anyone else's images.

So if these rings are very apparent in your stacked images after normal post processing in Photoshop etc, then you might try a different stacking parameter ?

I use AHD Debayering and Average or Median stacking.

YOUR STRETCHED FLAT ABOVE - RINGS SLIGHTLY VISIBLE

 

YOUR STRETCHED LIGHT ABOVE - RINGS HARDLY VISIBLE

 

MY STRETCHED 6D FLAT ABOVE

[Oddsocks]

On 27/02/2019 at 18:23, Spacehead said:

The rings are present even when I take an image of the floor - with no camera lens on - just the camera on its own, no scope or anything.

This is a puzzle and at first and I originally wrote a reply solely based on possible camera problems until I realised that some of your post processing is with .jpg's.

So this is a revised and heavily edited post.

The small scale concentric ring artefacts in your opening post .jpg stacks, are possibly caused by the data compression routines that create reduced size .jpg files.

For astronomy images you should be acquiring and post processing only with raw .CR2's or uncompressed 16/32 bit .tif's or .fit’s etc, never 8 bit .tif’s or .jpg’s as compression artefacts will appear.

The small scale and large scale ring artefacts in your raw .CR2 files are more of a mystery.

In your opening post you say that the rings appear even with no lens fitted to the camera and with the camera pointed towards the ground. When operated in this way vignetting should virtually disappear (except in cameras with full frame sensors that occupy most of the camera sensor well). 

With the APS sized sensors such as that found in your camera being quite small in relation to the diameter of the sensor well, the illuminated field, with no lens or telescope fitted, should only show linear gradients with virtually no vignetting present and therefore few if any rings visible when you stretch the image. 

A simple test you can do that may help to eliminate camera issues is to take an image pointing the camera at a plain white painted ceiling with the standard lens fitted and another with no lens then stretch as before, if the ring pattern, spacing, size and shape are identical in both images then possibly a sensor fault is present, if the ring pattern, spacing size and shape is different in both images then something is else is the cause.

If the ring artefact pattern is identical in the with-lens, without-lens images and I had to take a guess I would say that as your EOS1300D had been astro modified it might be that the anti-aliasing filter has been put back incorrectly, or is missing altogether, or there has been some dampness on the sensor at one time that has resulted in the antialiasing filter or far IR filter sticking to the sensor surface. Was this a full astro mod to the camera or just the first stage mod with only the near IR filter removed?

For daytime terrestrial imaging try to avoid .jpg's and keep to raws, or at least configure the camera to capture both simultaneously, if you absolutely have a need for only compressed .jpg images, such as to save space on the SD card etc then always use the highest quality .jpg compression algorithm that the camera supports, see the in-camera setting menu, but never use .jpg's for astro imaging.

I looked at your two linked .CR2 files, light and flat, in PixInsight and there are no ring artefacts visible at even quite high stretch, attached screen shot below, which makes me wonder if something else is going on with the post processing, is it possible your post processing application is working with a mixture of 8 bit and 16 or 32 bit images instead of all 16 or 32 bit?

For astro imaging capture and post process in raw .CR2, .fit’s or minimum 16 bit .tif etc. Jpg's for astro image processing are only fit for the trash can!

As Michael points out, stepped vignetting ring artefacts are to be expected when you stretch an image very hard so that across the whole image the intensity only varies by a few ADU counts and quantisation steps then become apparent. If your Barnard 33 / IC434  image is very faint, as it seems is the case in your posted images then it’s possible the stepped ring artefacts are a normal consequence of over-stretching to pull out data that is not really there in the first place. Do you see this pattern in all your astro images or just very faint, primarily Ha imges like this one, are the artefacts seen in normal daytime images?

Can’t think of anything else at the moment.

William.

P.s. noticed in the .CR2 file header that you have auto-rotate enabled in the camera settings (landscape/portrait automatic sensing), this should be temporarily disabled when used for astrophotography.

 

[Spacehead]

All - I think its better if I re-direct you to this thread now - which I have created in the hope it might help others with similar problems.
Thanks for all the time and effort you guys have put into this - it has helped me out massively.
https://stargazerslounge.com/topic/333055-my-rings-in-images-problem-is-solved/