Camera view does not show any object I have a strange effect with one blend file.
When I switch from the viewport view to camera view the camera does not see the object, although it is in the view. There rendered image shows the object again.
To test this effect I deleted all objects but one.
This is the scene:

This is what the camera view shows:

This is the final render:

The test file (1 MB) can be downloaded here.
In camera view press Home key on keyboard.
Keyboards without Home key can press fn+←.
This is a shortcut for command Frame Camera Bounds and can be found from View menu under Cameras.