CameraSpin.cs

using UnityEngine;
using System.Collections;

public class CameraSpin : MonoBehaviour {

    public float spinRate = 1f; 

    private Transform mainCamera; 

    public float boomStep = 2f;

    private const float boomMin = 2f;
    private const float boomMax = 1000f;

    // Use this for initialization
    void Start () {
        // assume first child is the camera
        mainCamera = transform.GetChild(0);
    }
    
    // Update is called once per frame
    void Update () {
        float boomLength = mainCamera.localPosition.z;

        if (Input.GetKey(KeyCode.RightArrow)) {
            transform.rotation *= Quaternion.AngleAxis( spinRate, Vector3.up);
        } else if (Input.GetKey(KeyCode.LeftArrow)) {
            transform.rotation *= Quaternion.AngleAxis( -spinRate, Vector3.up);
        } else if (Input.GetKey(KeyCode.UpArrow)) {
            transform.rotation *= Quaternion.AngleAxis( spinRate, Vector3.right);
        } else if (Input.GetKey(KeyCode.DownArrow)) {
            transform.rotation *= Quaternion.AngleAxis( -spinRate, Vector3.right);
        } else if (Input.GetKey(KeyCode.Equals)) {
            // shorten the boom 
            boomLength -= boomStep; 
            boomLength = Mathf.Max(boomLength, boomMin);
            Vector3 localP = mainCamera.localPosition;
            localP.z = boomLength;
            mainCamera.localPosition = localP;

        } else if (Input.GetKey(KeyCode.Minus)) {
            // lengthen the boom 
            boomLength += boomStep; 
            boomLength = Mathf.Min(boomLength, boomMax);
            Vector3 localP = mainCamera.localPosition;
            localP.z = boomLength;
            mainCamera.localPosition = localP;
        }   
    }
}