Weird artifacts in star trails image

I took a series of 30 sec exposures the other night and combined them into this image. However after playing around with the highlights, shadows, I noticed something strange in the center shadow area. There are these faint concentric curved lines in the image - one set oriented somewhat vertical, the other horizontal.

Take a look at the dark center portion toward the bottom where the treeline is, abov the lake. I increased the brightness and contrast a lot to make it more visible.

I used a Sony a6000 with Touit 12mm lens, and the Playmemories Timelapse app to take the images (30sec exposure each) and combined the images using StarStax.

Is this some kind of reflection or ghosting from the stars inside the lens or sensor? Or is something else causing it? It doesn't seem to follow the pattern of the stars, it appears to extend all the way to the bottom.

An example of a single image is at the bottom, I don't really see the pattern anywhere in the single images. Perhaps after stacking them on top of each other the pattern becomes visible and its just too faint to see in single images.

I don't know what's causing it but it looks like a Moire pattern to me.

The Milky Way galaxy

Are you stacking JPGs or RAW.

If you are stacking JPGS.  Then turn off all the in camera processing especially lens correction.  In this case my first guess on this pattern would be a lens distortion removal adjustment that as imperceptible artifacts until you stack which amplifies them.

Don't worry about how anemic the images look. I purposely exaggerated the post processing to make the effect more visible - otherwise it is faint but still visible.  Just wanted to make sure it was prominent for online viewing.

I don't think that program accepts Sony ARW files. So I tried to retain as much as possible by converting them to TIFF. Never used Jpeg.

Although I did output the TIFF from Capture one, not sure if its applying any lens correction, I don't even know if you can turn it off I never saw an option to remove the lens profile.

Wow thanks for posting that.  The pattern looks very similar to the one I had.

Actually I reran the stacking again using another program called StarTrails.  and the same pattern emerges.  I'm wondering if this is camera specific issue.

What camera did you use to create the image you posted?

Ok so I reran the stacking again and here are the results below -

NOTE: I went back and checked and the original image I posted in the original post is the result of stacked JPEGS.  I did another run using TIFF to rule out this being the result of some strange JPEG artifact.

I also tried another program StarTrails using both JPEG and TIFF source files.

From all stacks, I can conclude so far

All stacks from both programs resulted in the same pattern at the exact same location so either

A) they are using the exact same algorithm to stack images and this is a software fault

or B) regardless of algorithm used the problem is buried in the source images used

SarStax gap filling stack from TIFF source files

StarTrails gap filling stack form JPEG source files

StarTrails gap filling stack form TIFF source files

I'm thinking this is the camera that is generating this and the problem was captured in the ARW images, but not sure exactly what.  Or perhaps something to do with the conversion from ARW to TIFF/JPEG before stacking.

If these individual points of noise or faint light that end up being stacked into that pattern are there in the original captured ARW files, it could be some faint reflection of the stars through the lens, or perhaps some reflection in the sensor itself.  Noise is supposed to be random so can we rule out noise?

erotavlas wrote:

All stacks from both programs resulted in the same pattern at the exact same location so either

A) they are using the exact same algorithm to stack images and this is a software fault

or B) regardless of algorithm used the problem is buried in the source images used

Can you post some of the ARWs? Then I should be able to check if its from them. Actually, you might just try feeding one through my KARWY tool to see if the compression error in the file has a similar pattern.

This is really odd. It sure looks like artifacts from applying some lens correction, but it seems too dramatic for that. Could this be aspheric lens surface error -- the same stuff that causes onion skin bokeh?

I have a theory that it is a reflection of the micro lenses on the sensor reflected back off the rear lens surface.