<p>Shapes appearing stretched in the periphery is a consequence of perspective projection. The wider the field of view (FOV) is, the stronger the stretching effect gets.</p>

<p>To demonstrate the effect I wrote a quick example on ShaderToy: <a href="https://www.shadertoy.com/view/MltBW2" rel="noreferrer">https://www.shadertoy.com/view/MltBW2</a></p>

<p>As you can see on the images below (corresponding to FOV of 40, 80 and 120; if I didn't make any mistake), this becomes especially noticeable with wide FOV, like 90° and above.</p>

<p><a href="https://www.shadertoy.com/view/MltBW2" rel="noreferrer"><img src="https://i.sstatic.net/99bS1.png" alt="FOV 40°"></a>
<a href="https://www.shadertoy.com/view/MltBW2" rel="noreferrer"><img src="https://i.sstatic.net/pSDlz.png" alt="FOV 80°"></a>
<a href="https://www.shadertoy.com/view/MltBW2" rel="noreferrer"><img src="https://i.sstatic.net/K2fI7.png" alt="FOV 120°"></a></p>

CC BY-SA 4.0
2018-11-02T11:47:37.140Z
Nice example. It might help to have some kind of a texture (e.g. a grid) on the ground plane, though; otherwise it's hard to tell the difference between changing the view angle and just moving the camera. (See also: [dolly zoom](https://en.wikipedia.org/wiki/Dolly_zoom).)
Ilmari Karonen
CC BY-SA 4.0
2018-11-02T13:56:24.260Z
It should also be noted that this effect typically happens with a high-FOV relative to the distance of the objects from the camera. It looks unnatural because you usually don't see objects from *that close* to your eyes. At least, not without quickly turning your eyes.
Nicol Bolas
CC BY-SA 4.0
2018-11-02T07:07:36.833Z
2018-11-02T07:50:54.963Z
2018-11-02T07:50:54.963Z
Julien Guertault
<p><a href="https://i.sstatic.net/FEEVq.png" rel="noreferrer"><img src="https://i.sstatic.net/FEEVq.png" alt="enter image description here"></a>
<a href="https://i.sstatic.net/yBUh2.png" rel="noreferrer"><img src="https://i.sstatic.net/yBUh2.png" alt="enter image description here"></a></p>

<p>Some context. Above are the code and the resulting image for it in Peter Shirley's Raytracing in one weekend's book. As you can see from the code, he adds in some spheres. And yet in the final image there are 2 ellipsoids side by side. I just can't fathom why it is so, no matter how many time I looked at the code. Can anyone explain to me? Here's the link to the source code.
<a href="https://github.com/petershirley/raytracinginoneweekend" rel="noreferrer">https://github.com/petershirley/raytracinginoneweekend</a></p>

CC BY-SA 4.0
2018-11-02T05:29:12.040Z
This looks normal and is caused by the perspective camera being close to the spheres and having a large FOV value.
PaulHK
CC BY-SA 4.0
2018-11-02T11:00:24.527Z
Btw, this is not exclusive to ray tracing.
Sebastian Mach
<raytracing>
Raytracing: why are the spheres in the image below appear stretched?
Manh Nguyen
# Raytracing: why are the spheres in the image below appear stretched?

(Asked by: username_0 on 2018-11-02)

[![enter image description here](https://i.sstatic.net/FEEVq.png)](https://i.sstatic.net/FEEVq.png)
[![enter image description here](https://i.sstatic.net/yBUh2.png)](https://i.sstatic.net/yBUh2.png)

Some context. Above are the code and the resulting image for it in Peter Shirley's Raytracing in one weekend's book. As you can see from the code, he adds in some spheres. And yet in the final image there are 2 ellipsoids side by side. I just can't fathom why it is so, no matter how many time I looked at the code. Can anyone explain to me? Here's the link to the source code.
<https://github.com/petershirley/raytracinginoneweekend>

**Tags:** raytracing

> **Comments:**
> **username_1**: This looks normal and is caused by the perspective camera being close to the spheres and having a large FOV value.  
> **username_2**: Btw, this is not exclusive to ray tracing.  

---

## 1 answers

### Answer by username_3 on 2018-11-02. Score: 16 | Accepted answer

Shapes appearing stretched in the periphery is a consequence of perspective projection. The wider the field of view (FOV) is, the stronger the stretching effect gets.

To demonstrate the effect I wrote a quick example on ShaderToy: <https://www.shadertoy.com/view/MltBW2>

As you can see on the images below (corresponding to FOV of 40, 80 and 120; if I didn't make any mistake), this becomes especially noticeable with wide FOV, like 90° and above.

[![FOV 40°](https://i.sstatic.net/99bS1.png)](https://www.shadertoy.com/view/MltBW2)
[![FOV 80°](https://i.sstatic.net/pSDlz.png)](https://www.shadertoy.com/view/MltBW2)
[![FOV 120°](https://i.sstatic.net/K2fI7.png)](https://www.shadertoy.com/view/MltBW2)

> **Comments:**
> **username_4**: Nice example. It might help to have some kind of a texture (e.g. a grid) on the ground plane, though; otherwise it's hard to tell the difference between changing the view angle and just moving the camera. (See also: [dolly zoom](https://en.wikipedia.org/wiki/Dolly_zoom).)  
> **username_5**: It should also be noted that this effect typically happens with a high-FOV relative to the distance of the objects from the camera. It looks unnatural because you usually don't see objects from *that close* to your eyes. At least, not without quickly turning your eyes.  

---

