Leonardo DiCaprio Films Diner Scene With Regina Hall for P.T. Anderson Movie

Leonardo DiCaprio's all-in on Paul Thomas Anderson's new movie ... shooting in NorCal for the second day in a row -- and working alongside another uber-talented star.

TMZ has obtained video and photos of Leo out at a restaurant Tuesday afternoon opposite "Scary Movie" legend Regina Hall and a younger, unknown actress ... and it looked like he brought some cool confidence to the scene.

Check out the vid -- looks like PTA is giving the Oscar winner some notes while he's chowing down. He's clearly keeping calm -- although we're sure a regular patron or two might've flipped out! The reason we say that ... this appears to have been filmed out in the open.

Eyewitnesses tell us the production team didn't fully shut down the establishment for this shoot -- and, instead, pulled an old H'Wood budget-saving move by allowing regular business to flow while they only took up a few booths to film the scene. That's what's being claimed anyway ... and we'll say this, it sure looks like normies might've been hovering around.

Leo and Regina Hall grabbing lunch together??? Definitely a shock if you happened to be passing through his restaurant. To be fair, PTA's sorta known for his low-budget, indie filmmaking ... even if Leo's normally used to more luxurious catering and a slightly larger budget -- not to mention a much more closed set than what appears to be going on here.

Also worth noting ... all these pics and videos of Leo filming are low-key giving away a lot of clues about the film's story. To be clear, we don't officially know anything about the plot yet ... but if this doesn't look like some sort of family outing, we don't know what does!

Anyway, just another day on the job for Leo. We broke the story ... LDC was filming in the same small little NorCal town Monday as well, though that scene was a bit more frantic.

Leo was in full-blown costume and makeup Monday in a dirty-looking trench coat and disheveled beard -- definitely appearing worse for wear while cop cars seemingly chased him down.

The untitled flick doesn't have a release date yet or much more in the way of details ... but we do know Sean Penn's in it -- and it seems only a matter of time before he's spotted too.