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I'm trying to create a simple human mesh. While working on the torso, I noticed some shading errors. They look even worse when you move the camera around.

The one on the left is with shading set to smooth and subdivision set to 5 on basic, the one on the right is shading set to flat, and no subdivision.

here's it with smooth shading and basic subdivision and here's it with flat shading and no subdivision

Here's another one...

flat shading, 5x basic subdivision (not catmullclark)

I've found that I can replicate the effect by simply making vertices go into the mesh.

bad shading

Does anyone know how these could be fixed?

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As you have discovered, this can be caused by non-planar faces. Ngons are particularly susceptible to being non-planar, but this can happen to quads too.

You can fix these automatically by selecting everything (A), then pressing Split non-planar faces in 3D view > Header > Mesh > Cleanup:

enter image description here

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OK I noticed what the issue is, for anybody else having this problem it is caused by having an edge up against a single face. image of problem
Notice how there are multiple vertices up against the single face. The fix is quite simple, I used the knife tool to cut a line from the problem vertices to another corner of the object making a triangle, like so:

What this does is it allows your single face to bend like it wants to, instead of it just popping the vertices out of the way.

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  • $\begingroup$ Also make sure that the large ngon is connected to the edge, in the images in your question it looks to me like there are some disconnected bits.. Try selecting non-manifold geometry with Ctrl Shift Alt M in edit mode. $\endgroup$ – gandalf3 Oct 22 '14 at 2:12

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