Strange artifacts in a simple object I'm modeling a mirror. I created this frame by extruding planes for the outside part and then connecting both holes from the front and the back. I used and applied a mirror modifier for the Y axis.

Everything looks good until I render the file, it shows a strange line as you can see below in the screenshot. I can solve this by using a Subdivision modifier but then I lose the sharp edges. Tried adding more edge loops and beveling but it seems I'm missing something.

Is there anything I can do to avoid these artifacts when rendering?
The problem is that you have activated the Smooth Shading option of the T menu, but your object is a low-poly mesh. If you try to smooth a low-poly mesh these strange artifacts can happen. It's true that you have given your object a Subdivision Surface modifier that is used to simulate a high-poly mesh, but you have disabled its Display modifier in Viewport, so the artifacts still appear.

You say that you did that because you wanted to have both smooth and sharp edges.

If you want to have a smooth appearance but at the same time keep some sharp edges, add some additional edge loops close to the angles you want to keep sharp. Here is how: