JAVASCRIPT

camera helper three js

const camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 );
const helper = new THREE.CameraHelper( camera );
scene.add( helper );

camera in three js

camera is like a window to our scene.When defining a camera we create 
what is called a “frustum” — a mathematical term for a four-sided rectangular 
pyramid with the top cut off.
const perspectiveCamera = new THREE.PerspectiveCamera(
  50, // fov — Camera frustum vertical field of view.
  width / height, // aspect — Camera frustum aspect ratio.
  1, // near — Camera frustum near plane.
  2000 // far — Camera frustum far plane.
);
two most useful camera are the perspective camera and the orthographic camera.
1)Perspective camera — depth perception is emulated in order to
reflect the way the human eye perceives the world.
2)Orthographic camera —  there is no depth perception, so no matter where the
object is placed in the scene,it will look the same size. This is useful for 
isometric games, for instance.