<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:

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

```

I got results that look equivalent to yours:

![Mitsuba render with face normals](https://i.sstatic.net/LNG6X.png)


---

