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Ghost pattern in A68 images

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Post Options Post Options   Quote Bounce Flash Quote  Post ReplyReply Direct Link To This Post Topic: Ghost pattern in A68 images
    Posted: 10 July 2020 at 04:44
I'm getting a ghost pattern on dark A68 images after processing in Photoshop. I take multiple exposures of fireflies in the dark then open them all as layers in a photoshop document, change the blend mode to Lighten so all the fireflies show, so far so good. Then when I merge the layers down to one layer this ghost pattern appears. Here's a link to it in my flickr. Does anyone know what this is? Thank you.

Ghost pattern by Steve, on Flickr


Edited by stiuskr - 10 July 2020 at 11:27
 



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sybersitizen View Drop Down
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2020 at 05:56
I've seen similar patterns in Sony forums at DPReview that ultimately were blamed on lens corrections dictated by the camera - primarily vignetting correction. Can't say for sure that's what's happening to you, but it's a likely candidate. If I can find a couple of those threads I'll post links.

The effect here must be acerbated by the action of blending several exposures with slight pixel offsets, producing a moire effect on top of the more usual concentric circular pattern.
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2020 at 06:47
Originally posted by sybersitizen sybersitizen wrote:

I've seen similar patterns in Sony forums at DPReview that ultimately were blamed on lens corrections dictated by the camera - primarily vignetting correction ... If I can find a couple of those threads I'll post links.

Ah, here we go:

https://www.dpreview.com/forums/thread/3988133#forum-post-57558825

About midway down the page you'll see a couple of posts confirming reports of circular anomalies with various Sony cameras, along with links to many previous threads on the same subject.

The consensus has been that some degree of vignetting correction can actually get baked in to ARW files, not just JPEGs. Often, but not always, it can only be clearly seen after an image is heavily processed.
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2020 at 07:21
Congratulations on your first post here, Steve

The pattern reminds of the one I get with my Canon EOS R and Sigma 35/1.4 Art when lenscorrections are turned on. So, what syber says would also be my guess.
I think Photoshop does use the lenscorrections when available? Can you turn it off? I do not use Photoshop (or Lightroom) so I am of no use.
Why not follow me on Instagram? @Addy_101
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2020 at 15:58
Are you shooting raw or jpg? When shooting jpg you could check if shooting raw helps to solve the problem.

Automatic lens corrections on or off?
To test the theory that it might be caused by lens (vignetting) correction turning this off (both in camera and in your raw converter) is a way to check that.

And last but not least, welcome to Dyxum, you've been a member for quite some time but without posts you probably haven't been welcomed before.
Mind the bandwidth of others, don't link pictures larger then 1024 wide or 960 pix high, see here
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 July 2020 at 18:28
Here's another long and in-depth DPReview thread on the subject, from 2019:

https://www.dpreview.com/forums/thread/4359229
 



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Post Options Post Options   Quote Bounce Flash Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2020 at 03:33
Thanks so much for your research and posts. I'll look into these articles as I can make the time update as I work on it.
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Post Options Post Options   Quote Bounce Flash Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2020 at 03:38
Thanks for the welcome and the suggestions. I'll be working on these leads as I can make time. This is the first puzzle I haven't been able to solve without asking for help, the responses have been very encouraging, thanks again!
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Post Options Post Options   Quote Bounce Flash Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2020 at 03:43
I'll have to learn how to reply properly. I'm trying to post replies to your posts but my replies all end up at the bottom. Bear with me, I'll study up.
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2020 at 03:46
Originally posted by Bounce Flash Bounce Flash wrote:

I'll have to learn how to reply properly. I'm trying to post replies to your posts but my replies all end up at the bottom. Bear with me, I'll study up.

That's the way the forum software works. If you want to make it clear that you're replying to a specific post, you can use the 'Quote' option.
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