Carl Fitch, prosecuting, told Sheffield Crown Court how the elderly woman was walking through the Beckett Road and Copley Road area of the town at around 3pm on October 17 last year, when Paul Dempsey jumped out at her as she was passing an alleyway.
Dempsey, who had his face covered with a scarf and balaclava, began threatening the woman, before pulling out a knife and making stabbing motions.
Mr Fitch explained: "He told her: 'I want your bag'. The woman said he couldn't have it and Dempsey went on to say: 'Give me your bag. If you don't then you'll get this'.
"In his left hand he had a knife and was making stabbing motions by her stomach. Unperturbed by his words and actions, the woman hold of the bag, with her hand over the strap.
"Dempsey began pulling on her strap. He grabbed hold of her coat and there was a struggle. The woman fell over and Dempsey was able to grab hold of the bag and run off."
After stealing her bag, 41-year-old Dempsey took £300 from her purse.
Police received information connecting Dempsey, of Whittington Street in Doncaster town centre to the robbery a short time later.
Dempsey's partner, Lisa Staveley, also of Whittington Street, was captured discarding the bag nearby on CCTV. The money had been taken from the bag by this point.
In a statement read out in court, Demsey's victim said the incident had left her feeling 'extremely upset'.
"He was clearly looking for someone he could prey on. He picked me at 83-years-old, at 4"11, weighing seven stone, I'm very petite."
Dempsey pleaded guilty to one count of robbery and one count of possession of a bladed article in a public place at an earlier hearing.
Staveley, also aged 41, pleaded guilty to attempting to pervert the course of justice at an earlier hearing.
The court was told how Demsey has a long history of offences of robbery and theft.
Specifically, he has previously been convicted of a street robbery carried out against a 79-year-old woman, and of robbing an elderly couple at knifepoint after breaking into their hotel room.
Defending, James Baird, told the court that Dempsey, a heroin addict of many years, decided to rob the woman after his methadone prescription was cancelled in order to fund buying an alternative.
He conceded that Dempsey posed a danger to the public, and said the only mitigation he could offer on his behalf was his early guilty plea.
Judge Rachael Harrison sentenced Dempsey to seven-and-a-half years in prison, with an extended license period of three years, on the basis she believed he posed a 'substantial risk of serious danger to the public'.
As a result, he must serve at least two-thirds of his sentence in prison before he can be considered for release by the parole board.
Judge Harrison told Dempsey: "You are clearly a very dangerous man to very vulnerable people, when you decide you want their property."
She sentenced Staveley to 12 months in prison, suspended for two years, and ordered her complete a 30-day rehabilitation activity requirement.