Picture Prince William and Kate Middleton reclining on a balcony near the top of Eureka Tower in Melbourne.

Then imagine a photographer standing on a building near Southern Cross Station about a kilometre away, waiting to capture their every move with a huge lens.

That is how far away a paparazzi photographer is estimated to have been standing when snapping photographs of the topless Duchess of Cambridge on a private holiday with her husband in southern France last week.

The photographs have subsequently been published in the French magazine Closer and in an Irish newspaper, and have sparked widespread condemnation and questions about how far is too far when intruding on the privacy of the royals.

The photos are understood to have been taken using powerful, long lenses by photographers standing on a public road or footpath at a distance estimated at between 800 metres and 1.3 kilometres away.

Age photographer Penny Stephens climbed to the top of Media House, on the corner of Collins and Spencer streets, this morning and zoomed in on Eureka Tower in Southbank, which is about a kilometre away as the crow flies.

Using a 600 millimetre lens and a 2x extender on a Canon EOS 1D Mark IV camera, Stephens was able to zoom in on a balcony near the top of the tower and capture its details in remarkable detail.

Together, the camera equipment costs about $24,000 and weighs a little less than seven kilograms.

Stephens said Age photographers usually used the large lens to shoot sporting events, including the football and horse races.

"There's no way anyone standing on that balcony would know I was taking a photo," Stephens said.

"It would be be very easy to hide the fact that you were taking photos."

Stephens said she was using the full focal length to get the shot of the balcony.

The photo could be cropped tightly to show greater detail, although the photo would have been grainier.

The British press has branded the editors of Closer as "grinning perverts" while the photographer has been labelled a "peeping Tom".

Even the notorious tabloid The Sun, which sensationally ran photographs of Prince Harry naked in Las Vegas and regularly features topless glamour models on page three, has described the photographs of the Duchess of Cambridge lounging by a pool as "grossly intrusive".

One photographer who filmed the Duchess of Cambridge sunbathing has been revealed as a woman named Valerie Suau. The Mail on Sunday pointed out that her surname was pronounced "sewer".

An anonymous colleague of Suau said she did not take photographs of the duchess topless, but sunbathing in her bikini.

"Valerie is concerned by the fuss and is keeping a low profile," the colleague told the Mail on Sunday.

"She says she was given free rein to do what she liked, taking pictures of the couple enjoying themselves in full view of the road.

"There were other people around, including walkers and cyclists, as well as staff at the chateau.

"The duchess was sure to have known this, and perhaps should have been a bit more careful about displaying her body in such a prominent position."