BasicCameraZoom.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class BasicCameraZoom : MonoBehaviour {

	public float maxCamDistance = 10f;
	public float minCamFOV = 5f;
	public float fovSpeed = 1f;

	public Transform target;
	public Camera myCam;

	float initialFOV;

	// Use this for initialization
	void Start () {
		myCam = this.GetComponent<Camera>();
		initialFOV = myCam.fieldOfView;
	}

	void ResetFOV() {
		myCam.fieldOfView = initialFOV;
	}
	
	// Update is called once per frame
	void LateUpdate () {
		if (target == null) {
			ResetFOV();
		} else {
			myCam.transform.LookAt(target);
			if (Vector3.Distance(transform.position, target.position) > maxCamDistance) {
				if (myCam.fieldOfView <= minCamFOV) {
					myCam.fieldOfView = minCamFOV;
				} else {
					myCam.fieldOfView -= fovSpeed;
				}
			} else if (Vector3.Distance(transform.position, target.position) < maxCamDistance) {
				myCam.fieldOfView += fovSpeed;
				if (myCam.fieldOfView >= initialFOV) {
					ResetFOV();
				}
			}
		}
	}
}