According to conventional wisdom, the business of show throws away good actresses as soon as they hit a certain age. But certain performers have defied this trend and continue to work and find acclaim. At least two of them (Vanessa Redgrave and Judi Dench) are on display this weekend.

Redgrave recently appeared in the summing up of the recent adaptation of Ian McEwen’s “Atonement.” She appears in a similar vein in the “The Shell Seekers” (8 p.m., Hallmark), based on a popular novel by Rosamunde Pilcher. But in this film, Redgrave’s older character remains on screen for a lot more time.

While one could easily dismiss “The Shell Seekers” as a typically pretty Hallmark production set in various lovely locales, the film packs a lot of potboiler into its two-hour run. The 64-year-old Penelope Keeling (Redgrave) is first seen recovering from a heart attack and is almost immediately set upon by her greedy and indifferent children, who are eager to inherit their grandfather’s expensive paintings before Penelope dies or does something foolish with them.

¢ Judi Dench (“Casino Royale”) leads a strong ensemble cast in the three-part series “Cranford” on “Masterpiece” (8 p.m., Sunday, PBS). Based on a series of novels by Elizabeth Gaskell, a Victorian-era writer whose stories combine the intricate minuet of romantic love found in Jane Austen’s work and an attention to class distinctions and changing mores found in the novels of Charles Dickens.

Today’s highlights

¢ NASCAR action (6 p.m., Fox).

¢ Allison loses her hearing on “Medium” (7 p.m., NBC).

¢ Special effects dominate the 2005 adaptation of C.S. Lewis’ allegorical tale “The Chronicles of Narnia: The Lion, the Witch and the Wardrobe” (7 p.m., ABC).

¢ “Destroyed in Seconds: Greensburg, Kansas” (7 p.m., Discovery) documents efforts to rebuild a tornado-ravaged town using “green” technology.

¢ Scheduled on “48 Hours Mystery” (8 p.m., CBS): A judge gets too close to a divorce case.

¢ Robin tries to steal the sheriff’s loot on “Robin Hood” (8 p.m., BBC America).

¢ Martin Sheen and Ed Byrne appear on “The Graham Norton Show” (9 p.m., BBC America).

Sunday’s highlights

¢ Scheduled on “60 Minutes” (6 p.m., CBS): a doctor’s dedication to the poor in Haiti and Rwanda; Dallas convictions re-examined; an interview with Mary Tillman, the mother of the NFL star killed in Afghanistan.

¢ Lisa’s documentary profile of her family gets exhibited at the Sundance film festival on “The Simpsons” (7 p.m., Fox).

¢ “Nature” (7 p.m., PBS) looks at “superfish.”

¢ Brooke Shields guest stars on “Hannah Montana” (7 p.m., Disney).

¢ The rift with the Vatican grows on “The Tudors” (8 p.m., Showtime).

¢ On two episodes of “Dexter” (CBS), the ice-truck killer hits close to home (8 p.m.) before Dexter confronts him in the season finale (9 p.m.).

¢ Backfields in motion on “Law & Order: Special Victims Unit” (9 p.m., NBC).

¢ “This American Life” (9 p.m., Showtime), the story anthology series adapted from public radio, enters its second season. Ira Glass hosts.

¢ A botched deal leaves a sour feeling on “Brothers & Sisters” (9 p.m., ABC).