Subtle Grid Pattern in Blurred Background

[do_japan]

I wonder if anyone can talk about the technical reason behind this subtle, undesirable grid pattern that showed up in the background of this photo taken at f/5.6 on my Canon EF-S 55-250mm lens. I'm assuming it has something to do with the shape of the glass lens, and the fact that it's not a top end lens.

I managed to remove most of the effect in Lightroom by turning the clarity down to -100.

 

[Jeff15]

I cannot see your undesirable grid pattern ?

 

[do_japan]

I cannot see your undesirable grid pattern ?

Very subtle diagonal grid, most visible in the salmon colored region behind the bird.

 

[TCampbell]

The first thing I think of is... was there, in fact, actually a "grid" in the background (e.g. a chain-link fence or screening of some type?)

Out of focus blur will be in the shape of the aperture opening. Some lenses, depending on the arrangement of the aperture blades, can produce odd blur qualities.

I'm more inclined to believe there is something in the background such as a fence or screening, because the blur pattern runs on what appears to be almost perfect 45° angles. Getting a lens to do this would require odd shaped square-ish aperture openings and you'd have to hold the lens just right (and while not impossible, I think it unlikely).

It's probably not an issue with the camera itself. The sensor is based on rows and columns of photo-sites and if there's a sensor problem, it's likely to run in that direction.

 

[do_japan]

The first thing I think of is... was there, in fact, actually a "grid" in the background (e.g. a chain-link fence or screening of some type?)

No fence or screen, just Shirijo Castle in Japan.

Must be just a weird thing with the lens, the lighting, and the fact that the uniform background area makes it more obvious. Here's the photo after turning down the clarity all the way in light room. It's still BARELY noticeable just a tiny bit.

 

[Braineack]

some bird photographers will mask the subject and sharpen it, then add additional blur/denoise to the BG to soften it up.

 

[dxqcanada]

Hmm, is the background the roof of a building ... possibly the roof tiles are causing it ?

 

[do_japan]

Hmm, is the background the roof of a building ... possibly the roof tiles are causing it ?

The background is the roof of Shuri Castle in Okinawa. While there are tiles on the roof, they're no where near that uniform. I'm fairly certain this is a lens issue. Perhaps a subtle pattern left by the machine that polishes the glass lenses?

 

[KmH]

A bit depth issue with the gradients in the background?
Bit Depth

Pattern noise?
Fixed-pattern noise - Wikipedia

 

[DSP121]

Oh... that roof!
Do something about it, overall it's good!

 

[480sparky]

How about a crop of the full-sized image? I'm not seeing anything in the image that's posted.

 

[TreeofLifeStairs]

I definitely see it and I’ve got a couple thoughts. First, I don’t know if you’ve resized it and something in the algorithm caused it. Maybe it duplicated some lines or left out others, I don’t know. Second, since some people see it and others don’t, I wonder if it could be an issue with how a particular monitor represents it. I’m looking at it on an iPad Pro with the app.

These are just guesses though.