Hymns and Bible readings are beamed via the high-tech rear projection system that he installed.
Churchgoers often turn up with broken gadgets and requests to fix their digital TVs.
Others bring in old VHS cassette tapes that he spends hours in his shed - and lately in an office in his daughter's home as his house is undergoing earthquake repairs - transferring the precious family images to disc.
"I get a great deal of satisfaction from doing it," he said.
He walks twice daily. To everyone he meets, he offers to convert any old tapes they have free of charge.
"It gives a lot of people a lot of pleasure. Sometimes, people have never seen footage from their childhood. It's very special."
Born in Temuka in 1918 and named after his uncle Horace Prattley who died at the Battle of the Somme in World War I, Mr Longson was always inquisitive and handy. As a child, he built his own radio sets.
When war broke out in 1939, the railway clerical cadet volunteered for the Air Force and became involved in the secret world of radar.
Mr Longson was one of a few in New Zealand trained to use the Typex British-made cipher machines.
It scrambled morse code messages, enabling planes patrolling the coastline and hunting Japanese or German submarines, ships, or aircraft, to communicate in secret.
"The work was extremely hush-hush but highly interesting. And we knew that what we were doing was special," he said.
After the war, he returned to his railways job and soon became interested in ham radio.
The Amateur Radio Transmitters' Association has made him a life member.
The father of two used to build his own television sets - his first had a 15cm screen made from a radar tube.
His daughter Ruth tells how the neighbourhood children would gather at their house and marvel at the moving pictures.
Mr Longson retired in 1976 and his wife of 67 years, Brenda, died three years ago.
But he has remained busy, introducing technical innovations at church, and using a laptop computer and now his iPad for Facebook and email to stay in touch with friends and grandchildren.
Vicars from across the region call on his still steady hand to service their pipe or electronic organs.
"I can fix most things. I'm fortunate to be as good [in health] as I am," he said.
Ruth says he would rather be behind a TV set fixing it, than in front watching it.
Mr Longson agrees. "The way things work has always fascinated me."
