Probably written in the 1950's, this was a science fiction short story about a couple of guys who use radar technology from WWII to be able to see into the past. They film what they see and release movies of great events, such as the battle of the Alamo. They discover, however, that many events did not occur as told in history books. They have to recreate some falsehoods with actors to make the movies marketable. At the end, they make some mistake that causes the Federal Government to realize what they're doing. I think they filmed Pompeii being engulfed in ash and lava.
This sounds a lot like the 1947 story "E for Effort" by T. L. Sherred.
I'm not entirely sure it's radar the protagonists of this story use (although it may be) but they definitely make movies of great events, as you say.
They eventually get into trouble by filming controversial events (religious things, I think, and secret governmental things that led up to the 2 World Wars) and planned to turn their invention over to anyone who wanted to use it.
I was never sure exactly why (it's been a long time since I read it) but the inventors get put on trial, and finally, somehow, the invention sparks a war, perhaps because of the governments of the world's zeal to make sure it isn't used to reveal any more of their dirty little secrets.
There is a more detailed summary on Wikipedia here.