So expect to see Lady Mary (played by Michelle Dockery), the eldest daughter of the Crawley family, managing the estate in a gender-bending pinstripe shirt, necktie and waistcoat. Get ready for Edith ( Laura Carmichael ), Lady Mary’s younger sister and, since her marriage, the wealthy and socially superior Marchioness of Hexham , radiating glamour in a patterned velvet coat or heavily beaded gowns. And check Lady Cora (Elizabeth McGovern), as their mother, the Countess of Grantham , wearing a heavily embroidered blouse fashioned from a tulle scarf to welcome King George V and Queen Mary at Downton.

Image Left, Anna Mary Scott Robbins, the movie’s costume director, on the “Downton Abbey” set. Credit... Focus Features

A few weeks before the film premiere, Ms. Robbins, 41 , whose six-foot frame was clad in a practical black jumpsuit, sat in her compact studio in southwest London amid costumes for her next film (“ Last Letter From Your Lover ”), a mood board, a sewing machine and a well-stocked book shelf, to talk about crafting “Downton” style, and how it relates to clothes in the real world.

This interview has been edited and condensed.

Even though you are creating 1920s clothes, does the contemporary world inspire your work?

My starting point was the designers of the time. But this is the thing, what I’ve always said is that I love fashion and am very aware of fashion and the designers out there, and am digesting information as a designer in this modern age. So how I curate the costumes from the 1920s must to some extent be affected by my viewpoint as a contemporary woman.

Can you give an example?

I wanted to dress Lady Mary in a Fortuny Delphos gown. Mariano Fortuny didn’t design dresses with a V-neck, but I wanted to do something that felt contemporary and relevant so I reimagined the shape of that original dress and played around with various necklines and settled on this one, which is more dynamic, edgier and a bit cooler for Lady Mary. So that’s how I modernized something that was very much of its time.