Render error in refractive glass - unwanted shards appearing

[Anonymous]

Hi, 

I am working with a 700 frame animation of a glass bifocal lens. A handful of the frames are rendering with the bifocal segment showing these...shards. See attachment. What can be causing this? Is it something in my render settings that I need to change?

I'm using the mental ray renderer. The problem material is the Arch & Design Glass (Solid Geometry).

I'm brand new to 3ds Max and brand new to this forum, so please let me know what other information is required to help troubleshoot this problem.

[Brock_Lafond]

It could be a number of issues.

How thick is the glass? Is it made to real world scale?

Is the mesh topology clean? Try subdividing the mesh to smooth it out more.

[Anonymous]

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@Brock_Lafond wrote:

It could be a number of issues.

How thick is the glass? Is it made to real world scale?

Is the mesh topology clean? Try subdividing the mesh to smooth it out more.

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Brock- Thank you for your response.

The glass segment is only about 1 mm thick at its thickest part. It is built to real world scale. Is that not the way to go?

The mesh topology is clean as a whistle. And it's pretty well subdivided. And the normals are all pointing exactly as they should. I've attached a screen shot of the isolated glass segment with normals showing -- just in case that provides any insight.

I look forward to any suggestions you have. 

Thanks,

A. Mingus

[Stefan_L]

Just a guess:

In the Advanced Rendering Options section of the glass material there are two Cutoff Threshold values for reflections and refractions set to 0.01 by default. Set them to 0.00 and try again...

[Anonymous]

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@Stefan_L wrote:

Just a guess:

In the Advanced Rendering Options section of the glass material there are two Cutoff Threshold values for reflections and refractions set to 0.01 by default. Set them to 0.00 and try again...

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Hi Stefan_L,

I tried your suggestion, and unfortunately, I'm still getting these dents along the top of the bifocal segment.  (see attachment)

But thanks for your input!

A. Mingus

[Anonymous]

After working on this issue for over a week, the nature of the probelm has changed somewhat.

The top edge of the bifocal segment looks dented or chipped, but only when rendered. In clay view, the top edge is perfectly straight. When I examine the normals along the top edge, they look "wonky;" i.e., pointed in slightly different directions. If it is related to the strange normals along that edge, I have no idea how to fix it. I've tried resetting the normals, auto-smoothing the normals, averaging the normals along the top edge. I can't seem to get the crisp edge that I need.

Attachment shows "dented" edge and wonky normals (selected).

Please, any suggestions? I am out of ideas.

Thanks so much,

A.Mingus

[Stefan_L]

If things are getting inaccurate you may be out of scale and get some rounding errors.

Could you post a sample scene? ZIP it, or it won't attach...