# How to do perspective camera zoom?

We have a perspective camera looking at a cube that scales (increasing and decreasing) almost every frame.

The goal is that no matter the scaling of the rectangle we will always see it near the borders as the camera will dynamically adjust itself. When its scale/size is inside of the screen the camera should zoom in and when its scale/size is outside of the screen the camera should zoom out.

To adjust the camera on the cube, we tried to set the field of view (both vertically and horizontally) and we also tried to translate the camera by calculating the distance between the camera and the cube. In both cases we find it difficult to do and we have a little issue where the camera is jumping temporary between bool IsInSceen() when the cube is not scaling. So we would like a little help.

You will find the calculations for a perspective camera here:

http://docs.unity3d.com/Manual/FrustumSizeAtDistance.html

With a bit of algebra, you can solve for whatever you need to…adjust the FOV or move the camera. There are some open questions about exactly what you need from your description. So I’m going to give you a bit of simple starter code for a restricted situation. Let’s assume:

• The block has some ‘z’ depth
• The block is always taller than the aspect ratio of the camera (i.e. it is the height of the cube that determines the camera zoom.
• Zoom is done though movement, not changing the FOV.
• The camera is at (0,0,-something) with a rotation of (0,0,0).
• The cube is centered in the camera

Here is a bit of code. Start a new scene, attach the script below. Run the app and modify the size of the block in the Inspector.

``````#pragma strict

function Update() {
var frustumHeight = transform.localScale.y;
var distance = frustumHeight * 0.5 / Mathf.Tan(Camera.main.fieldOfView * 0.5 * Mathf.Deg2Rad);

// Since front side of the block is not at pivot
distance += transform.localScale.z * 0.5;

Camera.main.transform.position = Vector3.back * distance;

}
``````