What is causing this editor camera glitch?

It’s really difficult to zoom in because everything disappears. This only happens in the editor.
I don’t know if I’ve edited a setting on accident?

http://imgur.com/G4ZrdRL

Thank you!

It’s too complex to explain why this is happening. It is very technical and its not really a bug.

Here is a workaround:
Select an object in the scene and press “F” while the mouse is over the sceneview. This will focus on that object with a decent camera.
If there is no optimal object in your scene where you want to zoom into, simply make one as a dummy (like “editorCamCursor” and give it an icon in the inspector so you can easily find and move it.