Q: why does a purple dot appears on my camera?

Howdy MarioSequeira,

it sounds like you've got an anomlie only when in certain aspect ratios in the camera app. I would use the troubleshooting information in the following article to see if it helps you get it working correctly again. These steps in particular:

 

1. Make sure that the camera lens is clean. If you need to clean the lens, use a microfiber cloth. If you see dirt or debris inside the lens, take your device to an Apple Retail Store or Authorized Service Provider for more help.
2. Make sure that there’s nothing blocking the camera lens. If you’re using a case, try removing it.
   With iPhone 6 Plus, a metallic case or magnetic lens could interfere with optical image stabilization. If you have a metallic case or magnetic lens attachment, try taking a picture without it. Then compare the quality.
3. Adjust the focus by tapping on the person or object in the preview screen. You’ll see the screen pulse or briefly go in and out of focus as the camera adjusts. In photo mode, try to stay steady when adjusting the focus. If you move too far in any direction, the camera will automatically refocus to the center. In video mode, you can adjust the focus before you begin recording.

1. Force the app to close, then open the Camera app again.
2. Restart your device, then open the Camera app again.
3. If your device has a front and rear camera, try both cameras by tapping  (camera swap icon). 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.

Get help with the camera on your iPhone, iPad, or iPod touch

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Regards,

Sterling