John Kasmin is sitting in his west London townhouse surrounded by the work of artists he once represented. Some are better known than others. One is truly stratospheric. “People always say that I discovered David Hockney, as though he didn’t discover himself,” says the 89-year-old collector and art dealer who gave the Yorkshireman his first solo show. 

Six decades on, the pioneering gallerist is about to have his own starring moment in Kasmin’s Camera, a book and selling exhibition of his photographs at Lyndsey Ingram Gallery. The images, long concealed within innocuous black-backed photo albums, are “like a diary”, he says. Shot mostly on 35mm film, they show the artists at work, rest and play. Many are being brought to light for the first time: abstract expressionist Helen Frankenthaler smokes a cigarette in her New York studio; Howard Hodgkin stands in an Indian palace on the banks of the Ganges; and Frank Stella is spreadeagled in swimming shorts in Laguna Beach.

And yet, more than anyone else, his photographs are of Hockney: Hockney lounging around in the Kasmin Gallery, or sunbathing alongside fashion designer Ossie Clark and painter Patrick Procktor. A series in Los Angeles was taken shortly after he moved there in 1964, while others document a road trip along the Pacific Coast Highway. “We were really tremendous buddies,” says Kasmin, who captured his friend winning the John Moores Painting Prize in Liverpool in 1967; holidaying in France in 1969; and visiting his mother in Yorkshire in 1975. 

The two men have known each other since 1961, when Kasmin was running Bond Street’s New London Gallery – owned by Frank Lloyd and Harry Fischer, the founders of the adjacent Marlborough Fine Art – and Hockney was a student at the Royal College of Art. “What made me want to open a gallery was that I’d fallen in love with big American paintings,” says Kasmin. “I do get slightly edgy about being remembered primarily as the man who started David Hockney.”  

Nevertheless, Kasmin was instrumental in promoting his new acquaintance. “I tried to get them [Lloyd and Fischer] to take on David Hockney when he was still a student,” he recalls. “They said, ‘You can sell some of his work, but we think it’s trash.’ I couldn’t have it out in the gallery, but I would sell the odd bit from behind the velvet curtain.” 

When Kasmin struck out on his own as a dealer, his home became his HQ. “He used to have a kind of salon every Tuesday night,” Hockney has said of the time (the artist, now 86, was unavailable for an interview). “All kinds of people came, and I met the art world for the first time. [Kasmin] was very knowledgeable about pictures, and I was part of his eccentric taste.”

Kasmin first showed Hockney in his eponymous London gallery (the first architect-designed commercial space of its kind in the UK) in 1963. Called Pictures with People in, the Yorkshire artist’s figurative paintings made him “the odd man out” among the gallery’s roster of abstractionists such as Barnett Newman, Ad Reinhardt, Kenneth Noland, Morris Louis and Helen Frankenthaler. Yet the sense of camaraderie and collaboration in Kasmin and Hockney’s dealer-artist relationship is palpable in Kasmin’s images. In one pair of photographs, the men have their faces playfully squashed up against the gallery door – Hockney also painted this image of Kasmin. 

“Lyndsey [Ingram] has a theory that when David looks at me, you can see that he’s really fond of me,” says Kasmin. He adds, laughing: “Lyndsey is a Hockney worshipper.” Kasmin’s photographs of Hockney in India in 1977 are especially striking. “David was terribly unhappy as he’d had a falling-out with Henry Geldzahler [curator of 20th-century art at the Metropolitan Museum of Art],” Kasmin remembers of the trip to Mumbai, where he took his friend to cheer him up. “Look how grim he looks here!” he exclaims, pointing to a moody picture of Hockney at the Raj Mahal in Udaipur, Rajasthan. “He does gloom very well.”

A photo depicting Hockney sleeping at Dubai airport also stirs memories. “It’s an innocent picture of the horizontal genius… losing his American Express card! We discovered afterwards, when we arrived at the Taj Mahal Palace in Mumbai, that he hadn’t got his credit card. I think it’s at this point that he lost it.” 

Ingram admits being overwhelmed when presented with the albums. “There are so many good images, taken by someone who was not only in the most amazing places with the most amazing people, but who also had this ability to take very candid but very skilled photographs. They’re wonderfully romantic. It’s been really hard to whittle them down.” One hundred and six are included in the final exhibition selection, carefully chosen to present Kasmin’s most famous artist as part of a bigger picture that also included the art critic Clement Greenberg and fellow dealer Lawrence Rubin. The photographs are available as 8in x 10in prints in editions of 25 (£950 each). Selected images will be printed as 10in x 15in editions of 10, at £2,200.

“It’s rather nice having something to do when you’re a retired old chap,” chuckles Kasmin of the project. “It’s not so much about fame, glory or money – it’s the activity of it all.” At nearly 90, he is still impressively sprightly, gleefully recalling how his love affair with photography began. It’s an evocative tale that begins in 1950s Soho, in the home and gallery of Victor Musgrave, “an eccentric Bohemian poet and art dealer” and his Russian wife, Ida Kar – “a serious photographer of people – mostly artists”, whose work is featured in the National Portrait Gallery.

“I used to help Victor in his gallery. I was also the cook and, well, actually, I had to help him by being Ida’s lover so that she wouldn’t keep hammering on his door with an axe when he was in bed with [his mistress, dancer] Lotte Berk,” says Kasmin. “My first experience of cameras was having to pose naked on a red silk chaise longue while Ida trained her camera on my penis.” 

A photograph of his bottom also features prominently in his memory of the time. “David Hockney insisted on having it pinned up behind the mirror in his bedroom,” recalls Kasmin of the image, whose whereabouts today is unknown. “But it did crop up in a film about David’s life,” he adds. “To my amazement, my bottom subliminally flashed past.” 

The two remain close friends – although “I think he knows that I’m not that wild about his work of the past 30 years”, says Kasmin. How does he feel about being the featured artist of this show? “I think it’s hilarious!” he bursts out, pointing out proudly that one of his Hockney pictures from India is now in New York’s Morgan Library & Museum. “It’s like jumping to the other side of the counter. Instead of being the salesman, I’m now the goods.” 

Kasmin’s Camera is at Lyndsey Ingram, 20 Bourdon Street
London W1, from 26 June to 30 August