Whether it is rewinding back to the 1910s or fast forwarding into 2050, Bollywood filmmakers are going back and forth in time with films like "Teri Meri Kahaani" and "Dangerous Ishq", whose stories span over decades.

And what's their biggest challenge? It's in creating the right ambience and weaving a well-connected story.

Kunal Kohli's upcoming romantic offering "Teri Meri Kahaani", starring Shahid Kapoor and Priyanka Chopra, is set in three time periods -- 1910, 1960 and 2012. Each has its own flavour.

Similar is the case with Vikram Bhatt's "Dangerous Ishq", the story of which spans over 500 years. Though said to be based on the theme of reincarnation, the movie will see actors Rajniesh Duggal and Karisma Kapoor in varied looks as the story travels from one era to another.

According to film historian S.M.M. Ausaja, it is the writer's prerogative to pen a lucid script, the director's job to track trivial details, and the editor's work to cut a film in a way that the audience doesn't feel distracted.

"I feel content is king in such films. If a director makes the narrative less complex, it will be easier for the viewer to grasp it. Any confusion has to be credited to the script. Also, a lot depends on the depiction and the art direction. When you show a certain period in a film, it has to be well-researched," Ausaja told.

Bhatt, who went back to the 15th century for "Dangerous Ishq", says it took a good amount of team effort to shape up the film with the authenticity for each era intact.

"We did a lot of research in terms of setting, costumes, dialect and colour palette. Otherwise, we could have lost the authenticity. So whether it was art direction, costumes, dialogues or colour...all departments did their individual research and worked as a team to perfect the look of the film," Bhatt told.

In the recent past, the transition in the looks of characters and the ambience have been portrayed in films like "Veer Zaara", "Bachna Ae Haseeno", "Actionn Replay", "Love Aaj Kal", "Mausam", "7 Khoon Maaf" and "Rockstar".

Kohli, who had portrayed these changes in his hit 2004 love story "Hum Tum", says more than the sets, costumes and research, it was important to focus on how the story holds over the time zones.

"It's very important that the story holds over time zones. And how do I overcome the challenge of covering different time zones in a film? Well I write a good story," he quipped.

Kohli admits "Teri Meri Kahaani" reflects his perception of the 1960s and his fantasy about the 1910 period.

"Most of my research for the 1960s era came from my passion for films. I have watched a lot of Shammi Kapoor and Raj Kapoor films and enjoyed watching them. So the setting came naturally to me. Capturing the 1910 period was complete fantasy for me.

"But unlike the way many filmmakers show the pre-independence period with serious, khadi-clad individuals, I wanted to show it with some fun. I'm sure people had fun back then and fell in love; so, that's the aspect I have tried to capture. In the 2012 era, I wanted to show a contemporary take on relationships and how love is taken forward through SMS and BBM," he said.

Filmmakers, who chose to deal with the subject of reincarnation in movies like "Madhumati", "Prem", "Milan", "Kudrat", "Karan Arjun" and "Om Shanti Om", were also posed with the challenge of showcasing different time zones.

Bhatt insists the idea of going back and forth in time is not distracting for the audience.

"Whether there are three eras or five eras in a story... one film has one story, and that shouldn't be disjointed," he added.