Documentary filmmaker and Canon Ambassador Marcel Mettelsiefen is no stranger to filming in dangerous territories. Starting out as a freelance photojournalist almost 20 years ago, the German self-shooter has covered conflict zones across the world. Since branching out into filmmaking, he has shot award-winning documentaries in some of the most hostile environments on the planet.

For the Netflix documentary, In Her Hands, Marcel and co-director Tamana Ayazi, spent more than two years documenting the journey of Zarifa Ghafari, Afghanistan's youngest female mayor. "The challenge with every documentary is that you bond with your characters in a very intense way," he explains. "Documentary filmmaking is sneaking into someone's life and gaining their trust by giving yourself fully to the story – 5% of the work is filmmaking, the rest is becoming a friend, a therapist."

Here, he explains his approach to a project, the challenges he faced while filming In Her Hands, and how it developed into something much bigger than he and Zarifa ever imagined when they started.

In documentary filmmaking, finding your main character is key. Marcel's extensive work in Afghanistan meant that he had built up a network of connections. "You always start with an idea – in this case, a strong woman in a country dominated by men, trying to find her way into politics in the midst of turmoil," he explains. "With documentary filmmaking, you can break down political context into emotional storylines by finding characters who take you with them."

With decades of experience in hostile environments, Marcel drew on wisdom he gained from previous projects to keep him safe. "I've been covering conflict for 20 years and you have a gut feeling," he explains. "I'm not a risk-taker, and you can't control situations on the ground."

Working and filming with Tamana, his co-director, helped Marcel assess danger levels every day. "We were measuring it and trying to understand how far we could go, and a number of times, we said 'no'," he says. "It was a good mix of me being a foreigner and Tamana being from Afghanistan, and discussing what was smart and what was not a good idea."

Marcel's ambition with In Her Hands was to deliver a cinematic film, but it was crucial that his kit was easy to carry, which is why he opted for the Canon EOS C300 Mark III. "As a filmmaker without a team, I need to to be able to forget about the camera so that I can focus on everything else," he says. "I always try to travel light and still shoot cinematic footage, and this is exactly what this camera combines."

To keep his kitbag as light as possible, Marcel mostly shot with EF and EF-S lenses, including the Canon EF-S 17-55mm f/2.8 IS USM, which he favours for its 3-stops of in-built image stabilisation and its sharpness. When he had time to slow down and capture epic cinematic shots, he used prime lenses, including the Canon EF 85mm f/1.8 USM. "I also work a lot with the Canon EF 70-200mm f/2.8L IS III USM, as it's such an important tool to be able to observe the background," he adds.

Marcel stresses that after gaining the trust of your characters, shooting in sequences is the next focus point. "You have to understand structure: the beginning, middle and end," he says. "Being self-taught, I know I make my life easier if I think of sequences in order to be able to understand blocks."

With more than 400 hours of footage for In Her Hands, Marcel had to keep sequences in mind throughout the journey. "What I've learnt throughout my career is that as long as you film in sequences, then the puzzle at the end is easier to resolve," he explains. "Even though you don't always know where everything is going, if you have sequences, you have options when building the very complicated puzzle in the edit room."

Having shot with Cinema EOS cameras for such a long time and with years of experience in documentary shooting, Marcel is now adept at trusting the process. "There is no script for a documentary – you start a journey and you don't know where it will lead," he explains. "You just need a strong character and then you have a film, always. Just believe in the project. In the end, it will all work out."

After dedicating two and a half years of his professional life to the film, showing the documentary to Zarifa was a standout moment for Marcel. "With someone like Zarifa, there is so much work on both sides – the filmmaker and the character – with trust," he explains. "You want to treat everything with respect. After seeing the film, she felt unbelievably empowered.

"The responsibility you have is so big. These are vulnerable people. You have to pick how much to show, and you have to be so culturally sensitive and make everything emotionally engaging. I was relieved when we all agreed we managed to make a very strong film."