# Why does a lens automatically produce perspective?

1. Feb 14, 2012

### fisico30

Hello Forum,

can anyone explain why a camera, a lens, automatically creates perspective in an image?
Is it explainable with ray tracing?

thanks
fisico30

2. Feb 14, 2012

### Drakkith

Staff Emeritus
What do you mean by "creates perspective"?
Edit: I guess you could say it's simply an intrinsic result of focusing light.

3. Feb 15, 2012

### zoobyshoe

I don't know what you mean by the lens creating perspective. The perspective is in the scene, the lens focuses the light from the scene, the camera records the light patterns.

4. Feb 15, 2012

### Andy Resnick

If you are referring to 'depth perspective', the answer is that magnification varies with object distance. In terms of ray tracing, put two objects of equal size at the front-and-rear edges of the depth of focus and see what the image heights are.

5. Feb 15, 2012

### fisico30

Hello everyone,

so reality is 3D and lenses, cameras, are trying to reproduce that 3D reality on a 2D plane....

I have recently read about foreshortening in perspective. Depending on the distance, point of view and focal length of the lens, we can get certain geometric distorsions in the picture; parallel lines seem to go to the vanishing point and the farther the object the smaller it is....
Automatically, a camera introduces all these artifacts of perspective (sometimes they are exaggerated too). In wikipedia, perspective has two attributes:
Objects appear smaller as their distance from the observer increases;
Foreshortened: the size of an object's dimensions along the line of sight are relatively shorter than dimensions across the line of sight;

Telecentric lenses, which I mentioned some time ago, don't create perspective distorsions....
for example a cylinder that lies along the optical axis seems to converge to the vanishing point. The rear of the cylinder appears smaller and the body of the cylinder appears oblique since parallel lines seem to converge to the vanishing point...

fisico30

6. Feb 15, 2012

### fisico30

An artist, when drawing a scenary, uses the laws of perspective to recreate the same effect that we have when we look at the real 3D world....

It seems that lenses and optics somehow do the same....is that true?