National Portrait Gallery unveils Brian Schmidt photo by David Roberts

However, the Australia National University vice-chancellor found himself peering down the lens of a very different piece of equipment when photographer David Roberts took his portrait.

It was a 1920s-era US-made large-format camera "bastardised" with a modern base to stop it from wobbling.

It was the Victorian photographer's camera of choice to capture the Nobel laureate for the National Portrait Gallery's collection.

Schmidt admitted it "felt a little weird" staring down the unusual camera and knowing the photo would end up on the gallery's walls.

"We all get our picture taken at some point of our lives; the difference with this was the way it was taken with this huge, almost human-sized camera," he said.

In the black and white triptych, Roberts used large film about 20 centimetres by 50 centimetres wide to capture Schmidt "the man rather than the Nobel Prize-winning astrophysicist".

"What I try to do is get past the surface. It's really easy to take a photograph of what someone looks like but to go beyond that to . . . the things you can't see, like who this person is and what they're like, that's a trickier kind of thing," Roberts said.

"It takes the involvement of the person and Brian was very brave and let himself be seen as a person."

For his part, Schmidt said Roberts wanted him to be himself and think what he'd typically be thinking.

So what was he thinking in his portrait?

"Pondering the universe," he laughed.

"I've never really thought about what I look like when I ponder the universe."

Several of Roberts' photos are in the gallery, but the portrait of Schmidt is his first commission for the collection.

While his camera might not be user friendly, Roberts said the mix of "ancient and modern" using a large negative enhanced the tonality, resolution and detail of the end result.

"It's like having a great big sensor on a digital camera . . . but the process of doing it is conducive to portraiture; you have to take a lot more time, you can see a bit more and get a bit more involved with the whole process," he said.

The portrait was unveiled at the gallery's spring dinner on Thursday night, where Schmidt was the guest speaker.

While Roberts said he always put a lot of thought into portraits beforehand, he also aimed to be sensitive to the serendipity of the moment.

And he and Schmidt found some common ground during the shoot when they started discussing lenses and image capturing.

"There is a certain feel to these big pieces of film that's as good as we do with electronic detectors," Schmidt said.

"I'm not saying we can't do it digitally, but the normal photographer would not have access to a camera like that."