Triangular render errors

When rendering amodel using phong shading (activating “smooth”), I allways get these triangular render errors in the area between shadow and light. Looks like the smoothing simply stops working in these areas.


I have tried to both cleanup and to triangulate the mesh, but it doesn’t help. Only workaround is to add a subdiv modifier and thus make the triangular errors so small that they don’t show up to much.
The problem appears in both the internal renderer and in Cycles.
Do I do something wrong, or is this a known issue?

This is the classic terminator issue, you can resolve this by simply using a subsurf modifier.

Thanks for the reply Ace Dragon. I am aware that a subdiv modifier resolves it, but putting subdiv on every model in a scene takes it its toll on rendering time. Phong shading does not cause these anomalies in other software I have used, so I guess this is a renderer error in Blender. You call it the “terminator issue” - do you know if this is something that is on the list for resolving?

This is no easy fix. Most unbiased render engines suffer from this terminator artefact and only very few have found a solution so far. I wouldn’t hold my breath for a quick fix.