Things to consider when shooting through car window at night?
I'm making a short film that takes place mostly in a car at night. Will I need a polarizer to see the actors through the windshield?


A polarizer could help reduce reflections, but the best way to do such a shot if you desire no reflections is to shoot it in a way that there are no reflections to reduce. How you can best do this depends greatly on how you want the finished scene to look, particularly what angles you desire light to be illuminating your actors and the car's interior. One obvious solution would be to remove the windshield altogether.

Just because a scene takes place in a car at night doesn't mean you must shoot the scene at night - or even in an unmodified car.

Many of the tricks of the movie trade involve shooting in conditions that barely resemble the final look of the scene on screen. This was true in the film days just as it is true in the digital age. The use of green screens, CGI, etc. has expanded the possibilities of what can be done to footage after it is collected but the practice of using lighting and exposure to make a scene look different than it actually was when shot has been around almost as long as motion pictures have.

Most of those 'night' scenes you see in old westerns were shot in daylight with an 80B filter on the camera and the film underexposed by a couple of stops. So much so that the 80B and similar blue filters were nicknamed "American Midnight" filters in Europe. 

More than a few scenes in films with characters in cars were shot with the windshields and other glass (or even parts of the car's roof) removed. Often such scenes could be shot with multiple sets (glassless stationary vehicle, moving intact vehicle, fabricated sets resembling parts of the interior of the car) and edited together in a way that made them appear seamless.