Prasanna (Kamal Haasan) is nursed back to health by a classical singer Bhairavi (Srividya) after a bloody street-side fight. The two are slowly drawn to each other and decide to marry in spite of their age difference and a past relationship that Bhairavi is still inextricably tied to. In the meantime, Prasanna's father, Mahendran (Major Sundararajan) embarks on a relationship with the young Ranjani (Jayasudha). We soon find out that Ranjani is Bhairavi's daughter (born to her out of wedlock). Both relationships arrive at a dilemma with an unexpected twist when Bhairavi's long-lost husband, Pandiyan (Rajinikanth) comes into picture.

• Kamal Haasan as Prasanna
• Major Sundarrajan as Mahendran
• Srividya as M. R. Bhairavi
• Jayasudha as Ranjani
• Nagesh as Dr. Soori/Hari (the drunkard)
• Rajinikanth as Pandiyan (Abaswaram)
• Y. G. Mahendra (Special appearance)
• Kannadasan (Special appearance)
• Jaishankar (Special appearance)

Origin

The Sri Lankan newspaper Daily News stated that K. Balachander adapted the screenplay of 40 Carats – a 1973 American film directed by Milton Katselas, which narrated the story of Ann Stanley (Liv Ullmann), a widow who falls in love with the much younger Peter Latham (Edward Albert) – for his film Apoorva Raagangal. According to Balachander, he was also inspired by a riddle which featured in one of the stories in Baital Pachisi. Writer N. R. Dasan, however, stated that Apoorva Raagangal was his script.

When the matter was taken to the Madras High Court, it did not accept Dasan's contention for the script, hence handing the rights to Balachander. V. Govindarajan and J. Duraisamy produced the film under their production banner, Kalakendra Films. B. S. Lokanath was chosen as the cinematographer and N. R. Kittu as the editor, while Ramasamy was chosen as the art director.

Casting

Apoorva Raagangal was Kamal Haasan's first major breakthrough as a lead actor; for portraying the role of Prasanna authentically, Kamal took seven months to learn the mridangam. For the character's looks in the film, Kamal kept his moustache thin and hair long while also sporting bell-bottom pants and polo shirts. Srividya was assigned to play Bhairavi. Jayasudha was recruited to play as Srividya's daughter. Recalling her experience in an interview with Shobha Warrier of Rediff in May 2000, Jayasudha said that it was tough portraying the role of a young girl falling in love with an old man, " and Balachander Sir was a very tough taskmaster. He would not be satisfied unless he got 100 per cent from you. He used to reprimand me and shout at me if I messed up. I used to cry on the sets". Lyric writer Kannadasan and actor Jaishankar made cameo appearances as themselves in the film.

The film became noted for being the onscreen debut of Rajinikanth, who went on to become one of Tamil cinema's most successful actors. During his stay at the Film Chamber Institute in Chennai, Rajinikanth, then known by his real name, Shivaji Rao Gaekwad, was performing in a stage play and attracted the attention of Balachander, who subsequently telephoned Gaekwad and requested him to come for the auditions of his next film. At the auditions, Gaekwad imitated Sivaji Ganesan to prove his mettle to Balachander, but Balachander wanted Gaekwad to have an identity of his own and to perform without imitating the mannerisms of another person. Two days later, when Gaekwad was called again for a second audition, he took a cigar in his hand and threw it stylishly into his mouth, which impressed Balachander as he had not seen such unique mannerisms in any other actor that he came across since then. Balachander advised him to learn to speak Tamil, a recommendation that Gaekwad quickly followed.

When it came to christening Gaekwad with an on-screen name, Balachander came up with three options: Rajinikanth, Chandrakanth and Srikanth. Balachander chose to christen Gaekwad as Rajinikanth, after the name of a character played by A. V. M. Rajan from Balachander's film Major Chandrakanth (1966) on 27 March 1975; the name means "Colour of Night", which refers to Rajinikanth's skin colour. Rajinikanth played a relatively small but pivotal role of Pandiyan, the abusive husband of Bhairavi, in the film. Balachander revealed that Rajinikanth's first shot of opening the gate was deliberate and was representative of the actor making an entry into cinema through the film. Rajinikanth's make-up was done by R. Sundaramoorthy.

In October 2010, Rajinikanth's friend Raja Bahaddur recalled, "When he came to Bangalore, he told me about Balachander’s suggestion. Since my mother tongue is Tamil, we decided to speak in Tamil to each other. He picked up the language very fast and returned to Balachander. At that time, Balachander was launching his movie Apoorva Ragangal and cast him in it. Rajini hasn’t looked back". According to Rajinikanth's brother Satyanarayana Rao, "That first shot of the gate opening was shot five or six times, It was excellent! Even the onlookers remarked that this new find had style. But who was he, they wondered. It created a flutter".

Filming

The first day of filming was done in the Cashew farms of VGP Golden Beach with the song "Athisaya Raagam". Instead of implementing a tracking shot, the camera was moved manually by the cameraman while shooting for the song, making Apoorva Raagangal the first Tamil film to do so. Apoorva Raagangal was the first Tamil film to be shot in real houses without the use of any sets. It was also the first Tamil film to have a song ("Kelviyin Nayagane") in the climax sequences. The reason the song, "Kelviyin Nayagane", was included was because it provided the solutions to the problems faced by the film's characters.

Balachander wanted to shoot directly in houses without building sets, to give authenticity to what he wanted to convey in the film. With the help of Lokanath, he found houses which belonged to A. V. Meiyappan's family members. The scene was filmed on 27 March 1975, the same day when Balachander christened Rajinikanth. During the initial phases of the principal photography, Rajinikanth found Balachander's directing methods quite difficult to follow. Nagesh, who observed the newcomer’s difficulty, called Rajinikanth over and said, "Don’t get tensed up. Just imitate whatever Balachander is doing. That’s what I’m doing as well!" After listening to Nagesh's advice, it became easier for Rajinikanth to complete his portions in the film.

The film deals with the concept of relationships between people with wide age gaps, which challenged Indian social mores. It showed a young man who falls in love with a woman who belongs to the age of his mother, while a young woman is attracted to a man of her father's age. The dialogue "Ennudaya Appa Yarukku Maamanaro, Avarudaya Marumagalin Appa En Maganukku Mamanar, Appo Avarukkum Enakkum Enna Uravu" (English: My father is a father-in-law to someone; that person's daughter-in-law's father is my son's father-in-law. What is the relationship between him and me) sums up the theme of the film. According to Naman Ramachandran, the character of Pandiyan is not entirely negative. Pandiyan does not appear as a villain; in fact, he comes across as a saint. Pandiyan commits no villainous act. Rather, he voluntarily agrees to stay away from Bhairavi when he finds out that she is happy with Prasanna. Three things that happen immediately after Pandiyan’s death conclusively prove that the film does not see him as a villain. First, mournful music swells on the soundtrack, of a kind usually accorded to the death of a character who elicits sympathy; second, Bhairavi wipes off her sindoor, like a widow would after her husband’s death; and third, Pandiyan’s dead fingers are found to be clutching a note that says his last wish is to see the raga and taala meet, a clear reference to the proposed joint performance of the singing Bhairavi and the mridangam-playing Prasanna. So, Rajinikanth did not debut as a villain.^[7]

Like in many of Balachander's films, the female characters are named after carnatic ragas,^[31] such as Bhairavi (played by Srividya) and Ranjani (played by Jayasudha).^[32] According to G. Dhananjayan in his book Pride of Tamil Cinema: 1931 to 2013, Balachander used the technique of introducing the lead actors and actresses in the film with a title card in the name of a raga, symbolising their characters in the film.^[23] For Rajinikanth, the title Sruthi Bedam (English: A variation in the pitch.) was used to denote the twist in the tale with the appearance of his character.^[13]

The soundtrack was scored by M. S. Viswanathan and lyrics by Kannadasan.^[34] The soundtrack was released under the label of Saregama.^[33] The sound mixing process was supervised by J. J. Manickam and T. S. Ramasamy.^[6] The song "Ezhu Swarangalukkul" eventually becam