How to reverse camera direction tied to a path?

Question

I have tied a camera to an invisible box. Next I have tied the box to a path.

After adding key frames the camera inside the box moves through the path.

However, at some point of the animation, I would like the camera to "reverse". That is, I'd like the camera to follow the path as previous, but I'd like it to rotate to point to the other direction.

The illustration shows more precisely what I want to achieve. The camera circles around, rotates to point downward and goes up (zoom out from the plane).

Red - camera orientation

Black - camera movement

When I add a key frame on the box, or camera, Blender seems to ignore my settings. I suppose because box and camera are tied to the path.

Answer 1

1. Create the curve.
2. Add the cube, create a constraint for it: Follow Path, enable "Follow Curve" and click the "Animate Path" button.
3. Add the camera, parent it to the cube. At the beginning of the scene, set it to point along the path. Set a Rotation keyframe for the position before the camera should 'reverse'.
4. Go to the frame / time when you want the camera to rotate, add a second Rotation keyframe to the camera.

Example file below:

Answer 2

Drivers, Fixed Postion and Offset Factor.

99% of the time when using follow path, I don't bother with the parenting option, I rather just add the constraint and use fixed offset. Doing such allows me to animate the offset factor. 0 being the start of the curve, 1 the end.

Trig.

This one I've used some trig to drive the local Y rotation of the camera.

The inverse sine of 0 is 0 and of 1 is 90 degrees, so will double it. Negating it makes it spin inside my curve. Both blender and the math methods (like asin) use radians so there is no need to convert. If using "self" in drivers, the object being driven is self. The path can be grabbed from the constraint by right clicking over a field and "Copy Data Path" which yields the data path from self.

constraints["Follow Path"].offset_factor 

-2 * asin(self.constraints['Follow Path'].offset_factor)

Discrete change.

For this one have made the camera flip pi radians (180 degrees) instantly it hits the half way mark.

pi if self.constraints['Follow Path'].offset_factor > 0.5 else 0