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I am working on an animation of a product in blender using the Cycles renderer. The preview looks good, but the render shows uneven shading in an area. The only reason I can figure for that area looking different is there are a lot of very small polygons together. That being said, I don't know why the preview wouldn't show an issue.

What setting(s) could cause this kind of behavior?

EDIT: Solution

For future reference, I selected the problematic polygons using the Select Flat Face tool and then used the Remove Doubles tool. I tweaked the tolerance to keep sufficient detail and remove unneeded complexity.

Thank you to LukeD!

Render and Preview

I'm sorry I can't release the blend file because it includes design files that will not be made public.

I have checked and doublechecked that the "Viewport Visibility" and "Restrict Render" settings are the same for all the objects. I have reproduced the problem at multiple resolutions and number of samples.

Here are the render settings.

Render Settings

Thank you for your help.

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I've had this problem couple of times. I can't find in Blender manual anything about differences between preview and render but as far as I saw it preview isn't accurate like the final render.

In your case clearly geometry causes this shading (as in mine cases). For me only solution was to clean it up.

First of all try to remove doubles but if you want to make it 100% right you will need to retopologize this model.

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  • $\begingroup$ Thank you very much for the reply! I'm glad I'm not the only one with the issue. $\endgroup$ – engineer51 Aug 12 '16 at 0:38
  • $\begingroup$ @engineer51 when I started 3D only object's was important to me but with time I've started to pay attention to mesh/geometry - only quads, no booleans, just modeling porn ;) $\endgroup$ – cgslav Aug 12 '16 at 0:44
  • $\begingroup$ I tried re-exporting the model with less polygons from Solidworks to see if that would resolve the issue. It did not. I will try removing doubles and report back. It will be a few days before I can. Would the shrink-wrap feature be a valid way to retopologize? $\endgroup$ – engineer51 Aug 12 '16 at 0:49
  • $\begingroup$ I've had this problem while importing .obj form Catia. They where total mess. Sometimes only method is to redo whole model. Shrink wrap is not what you looking for. You can try 'Remesh' but I think it will not help at all. $\endgroup$ – cgslav Aug 12 '16 at 0:57
  • $\begingroup$ When you say redo the whole model, what would you suggest I do differently from Solidworks to Blender? I have been exporting from Solidworks as an high detail STL file and importing that into Blender. From there I have done no post processing (though I still plan to try removing doubles). $\endgroup$ – engineer51 Aug 12 '16 at 1:24

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