Because the first shift of POV in a film may jolt the audience’s experience, it works best where this brief ‘disconnection’ doesn’t hurt the story: after a climax.
The start of Act Two is a good place to move to the antagonist’s POV.
We have just seen that our protagonist is ready to take on the main mission of the film. He knows what he is up against, he may even have a plan on how to approach it.
At the beginning of Act Two, you can immediately increase the stakes by creating dramatic irony. You show the protagonist only knows half of the truth and the antagonist is really a lot more powerful and the protagonist may be missing a crucial piece of information.
The shift can happen to any other character, exceptionally even to an omniscient POV. But the most powerful and most frequently used POV outside the protagonist will be that of the antagonist.
Almost always does this increase the stakes as you show how well the villain is prepared, how much stronger this character is than we (and the protagonist) believed and what he/she is capable of.
One of my favourite Act Two opening scenes is in NORTH BY NORTHWEST. Roger Thornhill has to clear his name of the UN murder and he must find out why he is being mistaken for the mysterious Mr. Roger Kaplan.
At the opening of Act Two we are in a boardroom full of unknown faces. The audience’s instinctive reaction will be to find a character to empathise with, to latch on to. None such in this scene.
This is the Secret Service, discussing a fictitious agent, created by them as a decoy for the spies. Now Roger Thornhill has been identified by the spies as this imaginary agent, the secret’s service’s plan works better than hoped for.
Not only do we now know Thornhill’s predicament, we also realise he cannot expect any support from the government as confirmed in the last line of the scene, spoken by one of the agents:
Goodbye, Mr. Thornhill, wherever you are.
This scene shows how powerful a shift of POV can be to reveal an important piece of information the protagonist doesn’t have.
Another favorite example of dramatic irony created by a shifting point of view is taken from ONE FLEW OVER THE CUCKOO’S NEST and it constitutes the Mid Point Reversal.
McMurphy has just been on a fishing trip with his mates, sampling freedom outside the asylum.
The next scene shows the staff of the asylum discussing his fate, whether they should send him back to the work farm or keep him. McMurphy’s antagonist nurse Ratched drives the scene and the outcome is disastrous: he will stay in the asylum indefinitely.
When to Shift?
POV in Ratatouille’s Deleted Scene
POV as Controller of Tone