<p>The <code>box.obj</code> 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!</p>

<p>By adding this line to the box object in the scene file:</p>

<pre><code>&lt;boolean name="faceNormals" value="true"/&gt;
</code></pre>

<p>I got results that look equivalent to yours:</p>

<p><img src="https://i.sstatic.net/LNG6X.png" alt="Mitsuba render with face normals"></p>

CC BY-SA 4.0
2018-05-02T05:47:49.847Z
2018-05-02T05:47:49.847Z
Nathan Reed
<p>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?</p>

<p>edit: IOR of glass is 1.1 and outside is air.</p>

<p>Result of my renderer:
<a href="https://i.sstatic.net/4r0rF.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4r0rF.png" alt="Result of my renderer"></a></p>

<p>Result of mitsuba:
<a href="https://i.sstatic.net/A6vLt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/A6vLt.png" alt="Result of mitsuba"></a></p>

CC BY-SA 3.0
2018-05-01T21:24:09.160Z
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.
Nathan Reed
CC BY-SA 3.0
2018-05-01T21:33:47.477Z
[Here](https://drive.google.com/file/d/1BHOzY16NYf9h2aYsGTb3ZpRiSlVTwf88/) it is
Mustafa Işık
CC BY-SA 4.0
2018-05-02T08:28:14.967Z
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.
ivokabel
<raytracing><pathtracing><global-illumination><refraction>
Can a glass plate act like a lens?
Mustafa Işık
# Can a glass plate act like a lens?

(Asked by: username_0 on 2018-05-01)

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](https://i.sstatic.net/4r0rF.png)](https://i.sstatic.net/4r0rF.png)

Result of mitsuba:
[![Result of mitsuba](https://i.sstatic.net/A6vLt.png)](https://i.sstatic.net/A6vLt.png)

**Tags:** raytracing, pathtracing, global-illumination, refraction
> **Comments:**
> **username_1**: 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.  
> **username_0**: [Here](https://drive.google.com/file/d/1BHOzY16NYf9h2aYsGTb3ZpRiSlVTwf88/) it is  
> **username_2**: 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.  

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## 1 answers

### Answer by username_1 on 2018-05-02. Score: 8 | Accepted answer

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:


I got results that look equivalent to yours:


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