Last week, David Hockney accepted his last honorary degree. He used the occasion to tell Elaine Williams why students should swap their video cameras for pencils and look at the world afresh.

David Hockney is not impressed by Britain's art schools and he believes he has pinpointed the culprits - cameras and video cameras. The lens is a tyranny, he says. Video installations and photographic "realism" may dominate this summer's fine art degree shows, but Hockney has had his fill of this "dreary optical way" of looking at the world.

In the week that he received an honorary doctorate from Leeds University (sporting red corduroy slippers), Hockney criticised British art schools for "having an agenda to put across" and contributing to the demise of drawing. And because art is not an academic subject, art schools, he added, should not be in the business of awarding degrees.

"I have never really done any teaching and maybe I should have done. I am not power-mad enough. I realise that people who run art schools can be quite aggressive and they have an agenda to put across."

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The video camera dominates art, he complains. "It's a bore, it makes everything look a bit the same. If you look at things with a pencil and paper in your hand, you are going to see far more."

Hockney is as famous for his own work with cameras, fax machines and computer-manipulated images as he is for his paintings, but now, in his later years, painting is his abiding passion. He cannot understand why the love affair with the lens has led to the demise of drawing. Life-drawing studios have all but disappeared. "We need all kinds of artists. We have no need to destroy drawing. We lose so much. This wouldn't happen in music. John Cage would never say, 'You play it my way,' and get rid of all the traditional teachers."

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Last Friday, the day after receiving his Leeds doctorate, the 62-year-old Hockney was hard at work in Bradford - where he was brought up - painting a mural in the Salts Mill gallery, which boasts several of his paintings. The mural, a large painting of Punchinellos (traditional Italian puppets) will complement a display of Hockney's designs for opera sets, to open at the gallery in July.

Although Hockney opted for the sun, the lifestyle and the beautiful men of California 40 years ago, he has remained loyal to friends and family in Yorkshire. He has also painted them often, regularly visiting Laura, his mum, who died recently, in Bridlington, and building up the Salts Mill gallery with his friend, the late Jonathan Silver.

Despite losing a hearing aid he was keen to talk about his latest preoccupation, the way that looking through a lens has dominated our perception of the world. For the past year he has been investigating the use of optics in art since the Renaissance. His most recent paintings - a series of 12 portraits that go on show this week as part of the National Gallery's exhibition "Encounters: New Art from Old" - reflect this interest.

Hockney's thesis, which will appear in the book Secret Knowledge to be published next year, is that the development of lenses as artists' aids had a profound effect on the changing appearance of paintings from the mid-15th century onwards. He says: "People have been looking through cameras and projected images for a long, long time and art history has ignored the fact."

Hockney suspects that art students do not generally visit the National Gallery, but believes that if they did, they would find that artists from hundreds of years ago shared their preoccupation with the lens.

"Six hundred years ago Van Eyck must have known about the lens to produce that painting of Mr and Mrs Arnolfini (The Arnolfini Marriage, 1434) because, at the back of that painting, is a mirror that is a lens. It is an optical view of the world."

By contrast, the work of early-modern artists such as Cezanne is, he says, anti-optical. Cezanne was looking through two eyes, not through a lens towards a single vanishing point. "Cezanne was painting his doubts. When we question what the world looks like, it is about our relation to it. That was part of Cezanne's greatness. You cannot get that kind of grandeur through a lens.

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"The 20th century has been called a dismal century, more brutal, worse than any other. Nobody stood back to get the bigger picture. Something tells me that we are still not going to get the bigger picture if we are looking at the world through a little hole."

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Hockney is optimistic that drawing will make a comeback as a craft, particularly if young artists are to produce remotely interesting computer-aided art.

On a recent visit to the California Institute of the Arts, he found no one drawing in the fine art department, but there was a life-drawing studio in the department of animation. "Ultimately, they will produce something more interesting. That is bound to happen if you look at the world with a pencil in your hand," he says.

In Hockney's ideal art school he would admit students at 14 and teach them for as long as possible. A scholarship boy at Bradford Grammar, he deliberately neglected his academic studies to stay in lower grades because only exam failures were allowed to continue with art. "How old was Rembrandt when he went into the studio? The musical world would not let happen what the art world has let happen. Nobody would suggest that you shouldn't start playing the piano until the age of 20."

Hockney has always spent long periods drawing from life. When he first went to the Royal College of Art in London, he proved his skill by producing anatomical drawings before moving onto his experimental work. In order to qualify for his RCA diploma he was supposed to complete a written academic general studies course, but refused. He said he did not care about the diploma and made his own using a metal block in the print room. RCA head Robin Darwin, horrified at the prospect of failing Hockney, whom he had lined up for the rare distinction of a gold medal, waived the rules at the last minute. Hockney wowed the convocation ceremony by going up to receive his gold medal in a gold lame jacket, to deafening applause, but the episode still grates.

For he objects to art being treated as an academic subject. The triumph of "dreary optics" and conceptualism in art schools is, he says, the inevitable result. "I was at the RCA when they were abandoning life drawing and setting up the department of general studies. Later, the Royal College used to ask me for advice and I would say, 'Get rid of general studies and take up drawing again,' and they would reply, 'Well, you would say that, David. But we can't have people leaving here half-educated.' But there is no such thing as a dumb artist. Drawing is about teaching people to see: you learn a lot that way."

In particular, he objects to the effect on art schools of gaining degree status. "I couldn't believe it when the RCA spent such a considerable amount of time deciding whether it should confer BA or MA status on students. The only people who need degrees are dentists and brain surgeons."

The paradox, he says, is that so much knowledge has been lost in the process. "The RCA won't like me telling you this, but when I was a student the painting studios were at the back of the Victoria and Albert Museum, with north-facing windows. Then they built a new school with studios on top, facing east. The model (of the building) must have been there for some considerable time but nobody realised that with windows facing east the sun would stream in through the glass in the morning, which is hopeless. When I saw it I was shocked. That means nobody knew, nobody realised."

Given his views, Hockney has been reluctant to accept honorary doctorates. He did attend his doctorate ceremony at Leeds, but only when he was persuaded by "Melvyn", the university's chancellor, Lord Bragg. He maintained his reputation as a maverick by slipping away before the dinner. With four PhDs to his name (Bradford, RCA, Oxon are the others) this one, he says, will be his last.

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