Mr Cronin is the principal keeper of the lighthouse near Broadstairs in Kent, but by the end of November he and his five-man crew will have been replaced by a computer.
Their departure marks the end of 2,000 years of maritime history. One by one, the lighthouse men have been replaced by automation - leaving North Foreland as the last manned lighthouse in the British Isles.
On 26 November, the flag will be lowered for the last time and the door locked. It is one of the grimmer reminders of technology's impact on lives.
Trinity House, the lighthouse authority for England, Wales and the Channel Islands, estimates that automation has brought savings of pounds 5m a year. North Foreland's old telescope and barometer will be sold to a museum, and the new equipment installed and monitored from a base station in Harwich. The only visitors will be emergency engineers and the occasional cleaner.
It is a far cry from 1634 when Sir John Meldrum secured the right to light bonfires at North and South Foreland to warn sailors off the hazardous Goodwin Sands.
For the next four weeks, Mr Cronin and his crew will continue to provide 24-hour cover. The 500-watt halogen bulbs will be checked twice a day, the lenses cleaned and the windows washed down. The radio beacon will be monitored, weather reports compiled, and the log filled in. The nightly shipping forecast is no longer obligatory, merely a "comfort".
Mr Cronin, a bearded Irishman with piercing blue eyes, is sanguine about his impending redundancy. "Trinity House stopped recruiting in 1979 and we knew by 86 that it was going over to computers, so we've had a long time to get used to it," he said.
"It is very sad because it is the end of an era and it does mean the sailors will lose an extra pair of eyes. Although we no longer spend all night watching out to sea, we have always complemented the coastguard by passing them information.
"We know the tides and peculiarities of the currents, and if we're outside doing something, we're always looking out to sea."
Mr Cronin has spent all his 33 working years in lighthouses. He grew up on the Howth Peninsula in Ireland, and became friendly with the Irish lighthouse servicemen. His sister later married one of them.
"In those days it was 56 days on and 56 days off, which was a long stint, but in 1974 they changed it to month on and month off, which was much better for everyone. I still live in Dublin and just fly over when it's my turn to work."
He has worked on 15 lighthouses, from Lundy Island and The Lizard to the Nab Tower, off the Isle of Wight. He was a junior at the latter in 1972 when an oil tanker collided with the lighthouse, which is built on the seabed and rises up from the waves.
"I was on watch at 4am. I saw the tanker, but I thought it was coming to deliver oil and water. Then I realised it was a bit close and woke up the PK (principal keeper), who told me to `feck off'.
"Mind you, when we heard the grinding noise you've never seen anybody move so quickly."
The tanker was badly holed, but the lighthouse received only superficial damage.
Mr Cronin came to North Foreland in April to oversee the closure. After spending years in isolated towers in the middle of the sea, the small, 26m-high tower made a pleasant change. "This is a very good posting. It's on the mainland, so you can go off to the shops if you need to and you're not so cooped up."
But he has had his fair share of lonely night watches. "You had to have a hobby to help pass the time. I used to make ships in bottles, but that seems to have died out now.
"I'm also a radio ham andmade contact with people all round the world. Some of the others did knitting or lacemaking - it's a question of occupying the hands really."
He has had to learn to get along with colleagues. "There are six of you cooped up in a small space for weeks on end and you have to learn to bite your cheek.
"But I've made some very good friends over the years," he added.
Working at sea is a way of life he will miss even though he will be able to spend more time with his wife, Hilary, and their two children.
"It's very hard on the wives and they have to be fairly resourceful when their husbands are away for such long periods of time."
The lighthouse keepers remain a close-knit band and take their duties seriously. They have never been on strike.
"There is a sense of loyalty and duty and the knowledge that we provide an essential service. There is a feeling that there is a special relationship between us and the sea. We are the guardians of the sea."
But Mr Cronin has a new job lined up - in computers.