Documentaries are now shot by us. Yet are they the truth?

The Sheffield Documentary film festival is championing the slogan "The Truth is Out There", paradoxically in the year that the big documentaries that have made a splash have all been underpinned by a great lie that blurs the boundary between truth and fiction, and makes the truth irrelevant. These are films such as Banksy's Exit Through the Gift Shop, the Joaquin Phoenix documentary I'm Still Here and the Sundance hit Catfish.

But Sheffield's programmers have, in their 17th year, seen beyond the headline-makers and created a programme full of films that show that there has never been a better time to make or watch documentaries.

The big change for documentary film-makers is the amount of access they have, and the hours that they are now able to film; not just because camera technology has got better, but also because access to material has grown – simply because everyone has the potential to be a camera-person because most phones can now record video, and many can even record in high definition, making having to watch grainy, almost unwatchable, material shot on phones a thing of the past.

Depicting reality has always been the holy grail for documentary film-makers, with movements such as Direct Cinema and Cinéma Vérité all making valiant but ultimately failed attempts at doing so.

Now, though, directors are taking a different approach to finding reality. Instead of trying to hide the camera and pretend that it is not there, or hanging around for so long in the hope that their subjects eventually feel natural around them, they are more happy to take footage shot by other people and cut it together into a movie that depicts the truth, or the truth as the director sees it.

It doesn't always have to be mobile-phone or consumer-camera footage, either. Showing at Sheffield in the section called Documentaries Looking East is The Autobiography of Nicolae Ceausescu, which was a big hit at Cannes. Director Andrei Ujica has assembled this biography from official propaganda films, news footage, home-movie footage, and presents it without narration. In some of the more eerie aspects of the three-hour film Ujica also cuts out the sound to give a sense that the image says everything about the ego of the man. The fact that there is no narration, and little footage that seems manipulated by the director, adds to the sense that what we are seeing is a real and truthful depiction.

More traditional investigative journalism pieces are also benefiting from the ability of documentary film-makers to shoot footage quickly, with minimal hassle and, on occasion, clandestinely. One of the most anticipated films of the festival is The Battle for Barking, which follows the 2010 election battle for the seat of Barking and Dagenham.

Director Laura Fairrie has pulled off the feat of gaining excellent access to the British National Party in their attempt at building sufficiently on their support-base at local and European level to return an MP. The battle lines, and divisions, between the working classes and the middle classes, in what turned out to be a pivotal result as Labour candidate Margaret Hodge defied expectations to deliver the second-biggest gain of any of her party's candidates, fascinate the director as she follows the campaign.

The film appears in a section surprisingly titled "Documentaries get Political", surprising if only because one of the phenomena of the documentary world in the past two decades has been the success of Michael Moore and Errol Morris in bringing political documentary films to the multiplexes. What has thankfully died down is the craze started by Moore, and carried on by Morgan Spurlock, to make the director the star and protagonist.

Every film festival since Sundance in January seems to have a new film about the banking crisis, and Sheffield is no different with the world premiere of The Flaw. Director David Sington is the latest to try to explain what, exactly, went wrong and why, here through the use of interviews with experts, archive footage and animation. Like Michael Moore did with his seemingly prescient Capitalism: A Love Story, it attacks the political system that underpins Western liberal societies, especially America.

Elsewhere there's Sex Magic, Manifesting Maya, about a "sexual healer", and Nostalgia for the Light , about both cosmic exploration and Chile's dark past. A common occurrence at film festivals is the trend to have an environmental-documentary section. It's a sign of our times, and of the ticking time-bomb of global warming, and of the big question-marks over where energy will come from once oil runs out, that that this section is so popular.

The environmental documentaries on show a the festival suggest that nuclear technology is definitely not the answer when it comes to the energy crisis, because of the dangers posed by nuclear waste. Michael Madsen's Into Eternity questions the mentality of the Finns and their Onkalo project which aims to seal 300,000 tons of radioactive waste in a tunnel three miles underground, and that will supposedly last 100,000 years.

The danger posed should any nuclear waste escape is also made apparent in the world premiere of UK director Antony Butts's After the Apocalypse, which looks at the effects that the nuclear-testing programme carried out by the Soviet Union for 40 years after 1949 has had on the local populace. Butts takes a look at the increasingly appalling birth defects in each successive generation born in rural Semipalatinsk, Kazakhstan, where 456 bombs were dropped in an area known as "the polygon".

The best title of any film at the festival is Just Do It: Get Off your Arse and Change the World. This work-in-progress by activist and film-maker Emily James looks at those who make a job out of organising civil disobedience and protests. Segments of James's film will be shown to allow the audience opportunities to discuss with the director, perhaps on where truth can be found in documentary. The answer may just be in Sheffield.

Sheffield Documentary Festival (www.sheffdocfest.com) 3 to 7 November