After the moon was sighted Saturday night, Mehra flew to the capital Sunday with his crew to capture the festivities in Old Delhi.
"We decided some days ago to go ahead and shoot Eid in Chandni Chowk because it's a vital part of my film. If we had waited, we'd have to shoot next year. Besides we didn't need any of the actors," Mehta told.
"We just needed to shoot the incomparable morning-time festivity of Eid at Chandni Chowk. You can't capture that anywhere but in Chandni Chowk. No question of getting the same effect in a studio," he added.
Mehra's film, based on his growing-up years and youth in Chandni Chowk, will feature Abhishek Bachchan in the semi -autobiographical role.
Abhishek couldn't be there for the impromptu shooting of "Delhi 6" Sunday. But as soon as he returns from Namibia after shooting Goldie Behl's "Drona", the actor is expected to finalise the dates and sign the deal.
Present with Mehra at the half-day shoot of "Delhi 6" was cinematographer Binod Pradhan.
"I call him (Pradhan) the Van Gough of cinematography, and not just cinematography in Indian cinema but in any part of the world," Mehra said.
Most of the crew from "Rang De Basanti" will re-group again for "Delhi 6".