I am trying to implement rough dielectrics on my renderer. I compared the results of my renderer and Mitsuba renderer. However, a thin glass plate which is a cube scaled by (0.4, 0.4, 0.01) magnifies the object in front of it in Mitsuba while it does not magnify in my renderer. Do I miss something or does Mitsuba renderer do something wrong?

edit: IOR of glass is 1.1 and outside is air.

Result of my renderer: Result of my renderer

Result of mitsuba: Result of mitsuba

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    $\begingroup$ A thin glass plate should not magnify like this (if it did, you would see this every time you look through a window in real life!). Could you share how the glass plate is set up in your Mitsuba scene file? Perhaps there's something off about it. $\endgroup$ May 1, 2018 at 21:24
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    $\begingroup$ Here it is $\endgroup$ May 1, 2018 at 21:33
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    $\begingroup$ Just a side note: IoR of 1.1 is a heavily unrealistic value for glass, which is typically in interval 1.5-1.6 causing much stronger refraction effect. $\endgroup$
    – ivokabel
    May 2, 2018 at 8:28

1 Answer 1


The box.obj file has no vertex normals, and by default Mitsuba will generate smooth normals for OBJ files that don't specify their own normals. This creates the magnification effect: the box with smooth normals forms a convex lens!

By adding this line to the box object in the scene file:

<boolean name="faceNormals" value="true"/>

I got results that look equivalent to yours:

Mitsuba render with face normals


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