Camera zoom and background image in 2D game

Unity Engine
1

Hi All!
I’m working on Deep space rescue 2D space arcade game and wanted to add camera zoom in the beginning of a scene (look at first 3 seconds of video below to get the idea).
It works fine with simple coroutine

public class CameraZoom : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        StartCoroutine(ZoomIn());
    }

    IEnumerator ZoomIn()
    {
        Camera.main.orthographicSize = 100;

        while (Camera.main.orthographicSize > 5)
        { yield return new WaitForSeconds(0.01f);
            Camera.main.orthographicSize -= 1f;
        }
    }
}

but background image attached now to main camera as a child gameobject with sprite rendered (dark blue rectangle in video) obviously gets zoomed too.

How to change it so that background image always looks the same - fully zoomed in to full screen - regardless of Camera.main.orthographicSize?

Get game on Google play - https://play.google.com/store/apps/details?id=com.Omega486GameStudio.DeepSpaceRescue1

2

solved by myself - just resize gameobject holding background sprite:

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

public class CameraZoom : MonoBehaviour
{//for zoom in at level start

    private GameObject bg;

    void Start()
    {//background spriterenderer holder object
        bg = GameObject.Find("BG_Space");
      
        StartCoroutine(ZoomIn());
    }

    IEnumerator ZoomIn()
    {
        //zoom out instantly
        Camera.main.orthographicSize = 100;
        bg.transform.localScale = new Vector3(20, 20, 1);

        //calc bg zoom step
        float zs = (float)(20-1) / (float)(100-5); //calc: (init spriterenderer transform size - target size) / (init orthographicSize - target orthographicSize)
        Debug.Log("CameraZoom - ZoomIn, zs:" + zs);
      
        //zoom in smoothly
        while (Camera.main.orthographicSize > 5)
        { yield return new WaitForSeconds(0.01f);
            Camera.main.orthographicSize -= 1f;

            // Widen the object by x, y, and z values
            bg.transform.localScale -= new Vector3(zs, zs, 0);
          //  Debug.Log("CameraZoom - ZoomIn, bg.transform.localScale:" + bg.transform.localScale);
        }
    }
}