协程停止工作

我有两个带有协程的脚本。出于显而易见的原因，它在第一个中工作得很好，但在第二个中却没有。

它适用于此：

using System.Collections;
using UnityEngine;
using UnityEngine.UI;
using UnityStandardAssets.ImageEffects;

public class GameStartController : MonoBehaviour {
    public Button startButton;
    public GameObject cubeSpawner;

    // Use this for initialization
    private void Start() {
        startButton = startButton.GetComponent<Button>();   
    }

    public void StartGame() {
        EnableCubeSpawner();
        SpawnStartingCubes();
        HideStartMenu();
        StartCoroutine("FocusCamera");
        PlayBackgroundMusic();
    }

    // Enables the cube spawner, so it can start spawning cubes
    private void EnableCubeSpawner() {
        cubeSpawner.SetActive(true);
    }

    private void SpawnStartingCubes() {
        cubeSpawner.GetComponent<CubeSpawner>().GenerateStartingCubes();
    }

    private void PlayBackgroundMusic() {
        var audio = GameObject.FindWithTag("Audio").GetComponent<AudioController>();
        audio.PlayBackgroundMusic();
    }

    private void HideStartMenu() {
        startButton.transform.parent.GetComponent<CanvasGroup>().interactable = false;
        startButton.transform.parent.GetComponent<CanvasGroup>().alpha = 0f;
    }

    private IEnumerator FocusCamera() {
        var camera = GameObject.FindWithTag("MainCamera").GetComponent<Camera>();
        var velocity = 0f;

        while (Mathf.Abs(camera.GetComponent<DepthOfField>().aperture) > 0.001f) {
            Debug.Log(Mathf.Abs(camera.GetComponent<DepthOfField>().aperture));

            camera.GetComponent<DepthOfField>().aperture = Mathf.SmoothDamp(camera.GetComponent<DepthOfField>().aperture, 0f, ref velocity, 0.3f);
            yield return null;
        }

        camera.GetComponent<DepthOfField>().aperture = 0f;
    }
}

协程工作得很好，相机的光圈从0.6平稳地变为0。

但是，在第二个脚本中不会发生这种情况：

using System.Collections;
using System.Linq;
using UnityEngine;
using UnityStandardAssets.ImageEffects;

public class GameOverController : MonoBehaviour {
    public void EndGame() {
        StartCoroutine("UnfocusCamera");
        DisableCubeSpawner();
        DestroyAllCubes();
        StopBackgroundMusic();
        ShowStartMenu();
    }

    // Disables the cube spawner, so it can stop spawning cubes
    private void DisableCubeSpawner() {
        var cubeSpawner = GameObject.FindWithTag("CubeSpawner");
        cubeSpawner.SetActive(false);
    }

    private void DestroyAllCubes() {
        var gameObjects = FindObjectsOfType(typeof(GameObject));

        foreach (var gameObject in gameObjects.Where(gameObject => gameObject.name.Contains("Cube"))) {
            Destroy(gameObject);
        }
    }

    private void StopBackgroundMusic() {
        var audio = GameObject.FindWithTag("Audio").GetComponent<AudioController>();
        audio.StopBackgroundMusic();
    }

    private void ShowStartMenu() {
        var startMenu = GameObject.FindWithTag("StartMenu");
        startMenu.GetComponent<CanvasGroup>().interactable = true;
        startMenu.GetComponent<CanvasGroup>().alpha = 1f;
    }

    private IEnumerator UnfocusCamera() {
        var camera = GameObject.FindWithTag("MainCamera").GetComponent<Camera>();
        var velocity = 0f;

        while (camera.GetComponent<DepthOfField>().aperture < 0.6f) {
            Debug.Log(Mathf.Abs(camera.GetComponent<DepthOfField>().aperture));
            camera.GetComponent<DepthOfField>().aperture = Mathf.SmoothDamp(camera.GetComponent<DepthOfField>().aperture, 0.6f, ref velocity, 0.3f);
            yield return null;
        }

//        camera.GetComponent<DepthOfField>().aperture = 0f;
    }
}

它仅适用于一帧（光圈从0到0.03），然后停止。为什么会这样呢？