Image Anomaly-What Is It and What Causes It?

[LMB49]

I have a Sony a6600 camera body and a Sigma 100-400 mm f5-6.3 DG DN OS Contemporary lens that I purchased for bird photography. I eventually noticed what appears to be an anomalous pattern in the background of some of my bird photos that, to my eye, ruins the image. It consists of close-together, fuzzy lines running at an angle from the top left to lower right of the image. It tends to show up in photos with a complex background such as reeds, grasses, tree leafs, sandy or pebbly beaches and similar environments. I took the a6600 and the lens, along with photo samples of the anomaly, to the dealer I bought them from. He thought that the problem was with the a6600’s sensor and recommended sending it in to Sony, which was done. Sony did a “complete repair and return to factory specs, AF test, check, recalibration and realignment.” This did not fix the problem, which is still there.

I have included some of my RAW unprocessed (but cropped) images that show the anomaly. Have any of you seen this anomaly before and know what it is? Is it the sensor or some other issue with the a6600 or a lens problem? I sure would like to know so that I can get it resolved. Thanks.

 

[Deleted Member 5045]

Take some similar images at the same apertures with other lenses. This will tell you straight away if it's something to do with the camera.

The Sigma lens is a FF lens. Unlikely but could have something to do with it, maybe some type of weird glitch between it and the A6600...

 

[AlphaWorld]

The third one looks like there's a foreground green object.

The others might be something that I have seen called "double-line bokeh" (even though it can be triple line...). It's thought to be a lens artefact, not camera related, more associated with longer focal lengths. I can't give you the technical details, but if you search on that you may find more.

(hmm - some of the searches suggest it's related to image stabilisation - I hadn't seen that before, and apparently disagreement is rife!)

 

[AlphaWorld]

I shot one image when the bokeh looked super weird - in that case I was shooting through a net, and the net was invisible, but the effect on parts of the bokeh was horrid)

 

[Uncle Kevriano]

It's known as Nervous Bokeh, and it's one of those things that can't be helped. Often it's the wind moving things in the background, which kill any chance of a nice smooth backdrop, grass and bushes are the worst affected, or it's the way light is falling on the background. Have a google of that term, lots of ideas about it and it's causes.

 

[FowlersFreeTime]

It's known as Nervous Bokeh, and it's one of those things that can't be helped. Often it's the wind moving things in the background, which kill any chance of a nice smooth backdrop, grass and bushes are the worst affected, or it's the way light is falling on the background. Have a google of that term, lots of ideas about it and it's causes.

But Kev, haven't we seen other examples of nervous bokeh on this site with that lens? or am I imagining it?

 

[Uncle Kevriano]

But Kev, haven't we seen other examples of nervous bokeh on this site with that lens? or am I imagining it?

I think it occurs on any lens, it's not specific to a lens but more conditions. Other things that can cause this effect are shooting through double glazing, or using a filter, especially when using a very high res sensor, which picks up everything.
Take a look at Jabos Kingfisher post. Lots of this on there too