A Problem About RenderWithShader and Camera Orthographic

I currently meet a problem: I write a script to use RenderWithShader and I attach the script to my main camera. The main camera's projection is set to Perspective, and the RenderWithShader doesn't work. When I change the main camera's projection into Orthographic, the RenderWithShader work!

I don't know how this happen, and I just can't use RenderWithShader on my perspective camera.

My script:

 using UnityEngine;
 
 using System.Collections;
 
  
 
 public class DepthCamera : MonoBehaviour {
 
  
 
     public RenderTexture tempTexture1;
 
     public Shader depthShader;
 
  
 
     private Camera lightPosCam;
 
  
 
     void Awake()
 
     {
 
     }
 
     // Use this for initialization
 
     void Start () {
 
         GameObject lCam=new GameObject("LightPosCam");
 
         lCam.transform.position=transform.position;
 
         lCam.transform.rotation=transform.rotation;
 
         lightPosCam=(Camera)lCam.AddComponent(typeof(Camera));
 
         
 
         lightPosCam.CopyFrom(camera);
 
         lightPosCam.enabled = false;
 
  
 
         tempTexture1 = new RenderTexture(800, 600, 
 
                                          16, RenderTextureFormat.ARGBFloat);
 
         depthShader = Shader.Find("TestShader");
 
     }
 
  
 
     void OnGUI()
 
     {
 
         GUI.depth = 0;
 
         GUI.DrawTexture(new Rect(0, 400, 200, 200), tempTexture1);
 
     }
 
  
 
     // Update is called once per frame
 
     void Update () {
 
         lightPosCam.targetTexture = tempTexture1 ;
 
         lightPosCam.RenderWithShader(depthShader,"");
 
     }
 
     
 
 }

My shader:

 Shader "TestShader" {
 
     SubShader {
 
         Tags { "RenderType"="Opaque" }
 
         
 
         Pass
 
         {
 
             Fog {Mode off}
 
             
 
             Color (1,1,0,1)
 
         }
 
        }
 
 }

Please help!

Images of my problem: