Is this field curvature?

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Platographer Contributing Member • Posts: 569
Is this field curvature?

Below are two full-res test photos I took with my Sony A7Riv. I used the Sony 50mm f/1.8 (the one that is usually $248 or $198) at f/5.6 for the first one and the Sony 16-35mm GM f2/8 at 35mm f/2.8 for the second one. There is a weird variation in sharpness with both lenses--but especially with the 50mm--across the frame where there should not be any discernable difference in sharpness. To see this difference, look at the closest row of fencing (NOT the deck rail) that runs horizontally across the screen (especially the fence posts).

In the 50mm photo, the front row of the fence is generally pretty sharp, but gets extremely blurry in a portion right in front of the drain located on the right side (draw a line from the drain to the front fence row). The one fence post and some of the fencing on both sides is extremely blurry, but you can see it quickly sharpen up before you get to either neighboring post.

In the 35mm photo, the fence toward the left side of the photo is much sharper than the fence toward the right side of the photo (the leftmost front row fence post is slightly less sharp than its neighboring posts, albeit still sharper than the posts toward the right side of the photo). I focused on the drain, so the slight change in distance from the plane of the composition that the fence undergoes from one side to the other should, if anything, make it appear a little sharper as you move left since it gets slightly farther away (closer to the focal plane). This does not appear to be decentering, since the drain and the fencing that runs vertically on the right side appears sharper even though it is closer to the edge of the frame.

What is causing this? Both lenses were very clean, so I know that is not the problem.

Sony 50mm f/1.8 at f/5.6

Sony 16-35mm GM f/2.8 at 35mm f/2.8

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