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I'm rendering this scene in cycles (blender) on GPU with GTX 780 3GB In preview mode it takes about 2mins to render 2000 samples. render time in preview mode In final render mode it takes about 40 seconds render time in final render But i need to rotate scene and render it from different view. After rotation the model, render time has been increased to 20 times (to 20 mins per a frame) render time after rotate But in preview mode it still renders for 2 mins preview mode after rotatio

what's the problem? Problem appears only after rotating the object. If i moove the camera and NOT rotate the object it renders for 2 mins. But I need to rotate the object and not moove camera.

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I've posted at Blender's bug tracker and it seemed for first look as a bug, but Brecht Van Lommel (Rendering Software Engineer) explained:

This is a typical issue with raytracers, many long thin faces along one direction are difficult to fit well in a BVH unless the faces are aligned to the X/Y/Z axis. Also, the workaround is to subdivide the object more so the faces are not so long.

enter image description here

After subdivision mesh along faces render time decreased much.

LINK to this discussion on Blender's tracker.

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