It is possible!

First you need to select your Camera, then go to the _Properties_ panel, and under the _Camera_ tab, _Lens_ subsection, you can choose your lens type;

![enter image description here][1]

However, a perhaps little know feature, is that you can right click it (<kbd>RMB ![RMB][2]</kbd>) and select _Insert Keyframe_. Make sure the current frame is one before when you want your transition to happen and do this for the _Perspective_ lens.

![Animate][3]

Then just move to the next frame and repeat the process for the _Orthographic_ lens.


  [1]: https://i.sstatic.net/aOyFS.jpg
  [2]: https://i.sstatic.net/2j3vL.png
  [3]: https://i.sstatic.net/nyp3X.jpg