Hamilton's decision to leave McLaren at the end of the season after a 14-year working relationship has been the talk of the paddock ahead of this weekend's Japanese Grand Prix at Suzuka.
But when asked about why he had chosen to sign for the Silver Arrows, the 27-year-old said: "I don't want to talk about that this weekend. I have already spoken about that and I want to focus on this weekend."
Hamilton's reluctance to discuss his move did not prove popular with the international media, but the 2008 world champion appeared unmoved as he prepares for his final six races as a McLaren driver.
The 27-year-old currently trails championship leader Fernando Alonso by 52 points after retiring when leading the Singapore Grand Prix with a gearbox issue.
Hamilton has yet to taste victory at Suzuka, although he did win the 2007 Japanese Grand Prix, which was held at Fuji.
Hamilton admits he loves the popular figure-of-eight track and hopes to bounce back from his Singapore disappointment.
"I love coming here," he said. "The whole trip has been fantastic so far and the track is one of the best tracks in the world. It is not one that I have won at before but I think we have a car to win and hopefully it's a better weekend."
Hamilton's decision to leave McLaren has come as a disappointment to the team, but, when asked by Press Association Sport if he had spoken to his engineers and mechanics to explain his decision to leave, he said: "I have not spoken to them about it. This weekend it is business as usual. The focus is on trying to win and I know how professional they are."
Earlier, speaking to the British media, Hamilton had been more forthcoming.
Asked if it was a risk joining Mercedes, he said: "Not really.
"I've had such a great career with McLaren. I signed for McLaren when I was 13 and have had such an incredible journey with them.
"But in the end I had two offers on the table which were very similar but one was a lot more exciting. It's just a challenge.
"I could stay in the great car that I have, which I've worked really hard to help develop with the team, or go to a car that's not so well developed and help it."
He added: "No doubt it was one of the most difficult decisions I've faced in my life up to now.
"But a lot of other racing drivers, a lot of greats - (Alain) Prost and (Ayrton) Senna, they've all been with several teams.
"I don't think there is one who's been with one team for his whole career (1963 and 1965 world champion Jim Clark spent his entire career with Team Lotus).
"I'd been thinking for quite some time about what I wanted to do with my future, where I want to go, It's easy staying in the same place, but going somewhere else and taking on a new challenge is sometimes maybe even more exciting."
Asked if he felt he could battle for the title in 2013, Hamilton said: "No, I'm fully aware the car at the moment is not a world championship-winning car.
"The car that I'm in right now is a car that I've developed. Next year will be an evolution of the car that I've helped develop (at McLaren) and that will be a championship contender.
"But we (Mercedes) will work very, very hard to have a better year next year, but it takes time. You don't just arrive and things change. I think the focus is more long-term.
"If I can go there, help them progress, if we get some wins, if we eventually win the world championship - that's going to be an incredible feeling for all of us."