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I understand from your post that when using the Camera app or other third party apps with the camera that you see a black screen. The following article has some information which may be helpful in resolving this type of issue:
Get help with the camera on your iPhone, iPad, or iPod touch - Apple Support
You see a closed lens or black screen
If you see a closed lens or black screen when you open the Camera app, try these steps:
- Make sure that there’s nothing blocking the camera lens. If you’re using a case, try removing it.
- Force the app to close, then open the Camera app again.
- Restart your device, then open the Camera app again.
- If your device has a front and rear camera, try both cameras by tapping . If you see the closed lens or black screen on only one camera, take your device to an Apple Retail Store or Authorized Service Provider for more help.