Occasional spot blur

Who can explain occasional spot blur happening on otherwise sharp images? Camera & lens are like new.

One can see blur on the building in the center of an image

No blur

Atsel wrote:

Who can explain occasional spot blur happening on otherwise sharp images? Camera & lens are like new.

One can see blur on the building in the center of an image

No blur

Hmm, it could be heat wave distortion caused by the warm sunny building vs. the cold surrounding air, though if the second shot was immediately after the first I'd expect to see it in both. Otherwise, I'd guess it's some kind of strange IBIS anomaly - Does the camera automatically set the IBIS for 85mm to work with Viltrox? Is the firmware up-to date for both the lens and camera?

Are these with the MS or ES? I've seen weird hard to explain stuff happen with the ES on occasion too.

Erik Baumgartner wrote:

Hmm, it could be heat wave distortion caused by the warm sunny building vs. the cold surrounding air, though if the second shot was immediately after the first I'd expect to see it in both.

Images are 4 sec apart

Otherwise, I'd guess it's some kind of strange IBIS anomaly - Does the camera automatically set the IBIS for 85mm to work with Viltrox?

The lens electronically communicates with the camera. AF works, etc. The focal length is present in EXIF without manual tweaking.

Is the firmware up-to date for both the lens and camera?

Yes

Are these with the MS or ES? I've seen weird hard to explain stuff happen with the ES on occasion too.

It is ES

Regardless of them being 4 seconds apart, I'm still going to say it's atmospheric disturbance.  Not only could it be heat waves from sun warming, but you have buildings below.  Who knows what could be going on there.  Steam vents, exhaust vents, etc.  And a little breeze in the air would quickly move it around and perhaps away from one shot to the next.

The top of the building in the center is blurry on this image taken 4 sec before

Another example of strange sharpness distribution

Atsel wrote:

The top of the building in the center is blurry on this image taken 4 sec before

Another example of strange sharpness distribution

Have you observed this anomaly with any other lens, or on any other occasion?

...Or with using the MS?

Erik Baumgartner wrote:

Have you observed this anomaly with any other lens, or on any other occasion?

...Or with using the MS?

I have never seen such an obvious example with blur in the center of an image. Otherwise it is easy to take for lens softness.

Maybe I should re-test this with ES and MS in a row.

Atsel wrote:

Erik Baumgartner wrote:

Have you observed this anomaly with any other lens, or on any other occasion?

...Or with using the MS?

I have never seen such an obvious example with blur in the center of an image. Otherwise it is easy to take for lens softness.

Maybe I should re-test this with ES and MS in a row.

Probably not the cause, but it’s worth a try. It could certainly have just been some camera shake and and/or an IBIS glitch, but If it hasn’t happened on other occasions, it might indeed be an atmospheric issue - the softness is where the heat from the sun would be the greatest, and the effect can waver around quite a bit.

Comparing three images side-by-side, I would say another hypothesis, that it is extreme case of field curvature. Sharp parts on these images are slightly different.

f/5.6 image is focused perfectly in center, sides are softer;

f/5 and f/8 images are misfocused (AF was single & central point), though sides are sharper.

Infinity focus is always challenging on a portrait lens even @f/8!

Atsel wrote:

Comparing three images side-by-side, I would say another hypothesis, that it is extreme case of field curvature. Sharp parts on these images are slightly different.

Infinity focus is always challenging on a portrait lens even @f/8!

I have a similar issue with my Samyang 50mm F1.2 when used for example at f/8 and focused near infinity. Some random parts of the image turn out soft.