Of all the subjects I have photographed, the most controversial and the one that has moved me the most has to be the prostitutes who are getting on in years. They are true survivors.

"Plaza de la Soledad" is a documentary about Carmen, Lety, Raquel and Esther, four strong women - middle-aged and older - who want to break a vicious circle that began with abuse and abandonment suffered from an early age. They simply want to have a better life. The film follows their quest to find true love and their capacity to transform themselves.

I have had the opportunity to meet men and women working in the sex trade in my travels to Mexico's northern and southern borders.

I have been exploring [Mexico City's] La Merced, [a public market famous for prostitution,] on and off for the last 23 years. The prostitutes and their world have been the main subjects of my photographs.

My biggest challenge was moving from photography to film without losing my way of working - which is very intimate and learning to collaborate with more people, since photography for me is a very solitary process.

I am in any way glorifying or simplifying prostitution. The reality of prostitutes around the world is so complex. I've tried to focus on the humanity.

[My favourite are] the films of Agnes Varda, because of her sense of humor and the intimate, personal way she tells her stories. She is brave in taking creative risks, and her curiosity in others is so contagious. This brings me closer to the subjects in her films.