Michael Hoppen, 53, is one of the UK's leading photography dealers, having exhibited and sold the works of artists including Diane Arbus and Henri Cartier-Bresson. He has been the director of Chelsea's Michael Hoppen Gallery since 1993. He lives in west London
I first met Adam around 10 years ago. We had a show of Jacques Henri Lartigue, one of the great French photographers: Adam purchased a wonderful picture by him, which shows the 20th century appearing in the shape of a car on the left and the 19th century disappearing in the shape of a horse and carriage on the right. It's an important moment in photographic history, and it was quite surprising that he came in and knew exactly what he wanted.
We didn't really meet for a number of years after that, but he reappeared on the scene when we started specialising in Japanese photography. He has been to Japan many times with U2, and had a fascination in the images and the history behind them, and has built up a collection of post-war Japanese photography. We get some people who come in and say, "I want a photograph about this size," which makes my heart sink, but Adam is drawn to specific images.
Are we similar? He'd probably say I was tone-deaf, but the most important thing that we share is a passion for creativity.
We never really talk about music. I like U2 as a band, but I gravitate more towards jazz. When we have social time together, we'll go to galleries or museums. And we always email each other about things we've seen and have found interesting, or I'll call him and say, "If you're in New York, you should go and see such and such an artist."
I most admire his diligence: he's not a dilettante or buying pictures as it's trendy. You must remember U2 have worked with some incredibly talented artists such as [the photographer] Anton Corbijn. In fact, we had an exhibition called 22, which was 22 pictures of U2 over 22 years by Corbijn. That shows the mettle of both Adam and the band: where others would chop and change who they work with according to fashion, there's a level of consistency there.
My favourite memory of Adam is when he saw the work of Shomei Tomatsu for the first time, and, like me, just said, "This guy's unbelievable." It's tremendous when someone you respect sees the same thing in a work that you do. You don't even need to say that much: that's the art of great art.
Adam Clayton, 50, is the bassist for the Irish rock band U2, with whom he has released 12 studio albums and sold more than 150 million records worldwide. He lives in Ireland and France
The first I heard about Michael was through [the fashion designer] John Rocha. John had recommended Michael to me as the go-to guy for photography. I'd started collecting some pieces in the early 1990s, when I was living in New York: Robert Mapplethorpe, Diane Arbus, Man Ray. I was really just dipping my toe in the water, and I stopped for a long time after that. Then my friend Naomi Campbell gave me this Lartigue photograph and, as it happened, Michael was having a Lartigue show at the same time, so I went to it, and connected with him immediately.
What marks Michael out as a dealer is his passion: he collects as much as his clients. The art market was very different before the mid-1980s: then, art was all about passion, whereas now it's become a commodity. In that way, I think Michael is very much rooted in the old-school. He doesn't just sell to you, he informs you. He can teach you how to look and really see things. If I'm in London and have time off, usually on a Saturday, I'll give him a call and see what [exhibition] he has on, and what usually starts out as a 45-minute visit turns into a couple of hours.
There are two types of collector, I think. There are those who are quite academic, and get into the archaeology of finding the earliest example of a particular idea. Then there are those interested in what's new. I'm in the latter category, probably as I have a great interest in popular culture. That's where Michael is great: he puts an awful lot of stuff under my nose, such as Japanese photography. My interest in that came out of a feeling of boredom. I felt the big American photographers – the Walker Evans, the Ansell Adams, the Irving Penns – were over-exposed, that they had colonised our minds in terms of visual imagery. Also with U2, our artistry has always been bound up with the mythology of America, and I had grown tired of it. So when Michael said, "Why don't you look at what's going on in Japan? They're very undervalued, but doing very high-quality things," it was refreshing.
Michael is much more open-minded than I am. He lets everything in, which is admirable, while I edit quite a lot simply.
I'm sure Michael listens to music, but he's not interested in my opinion of it and that's fair enough – he's not interested in what I had for breakfast either. In the music business, there's a big star system and a degree of drama and glamour. Once you get away from that, you find much more measured people and I prefer to be around that. That's what I find in the art world, and that's what I find in Michael.
The first European show of the US photographer Robert Bergman's colour portraits is at the Michael Hoppen Gallery, 3 Jubilee Place, London SW3 (michael hoppengallery.com) until 27 November