The front is invisible and the back faces are solid. I tried to paste a screenshot directly to this post but it gives me a 'bad request' error on posting so it's here as a link https://app.screencast.com/UvIhzM0mfrUaa
OK thanks. This makes sense. If you extrude +z then normals are fine but if you extrude in -z (as in the video) you get reversed normals.
So why doesn't the teacher have the same problem? Was there an edit?
Hmmm ok. I've tried to replicate with a new circle and extruding down -z and all the new ones now output normal outward facing normals. The only way I've been able to get red normals on the outside by extruding down on the -z is to flip the circle. It's a gotcha for me as this just doesn't happen in C4D. You can find normals reversed but it only really happens as a result of detailed mesh editing and joining edges between separate models
That's because C4D is designed with 3D motion graphics as it's main focus. Blender is designed with 3D animation as it's main focus. There are several uses for having normals inside instead of outside. For example inverted hull method uses to create outline for NPR animation.
