Thanks a lot for your answers.

Thank you Eric.

Thanks a lot Michael! I get it. It's all about metering and exposing well from the start.

Thanks Michael. As I said to Indie Guy, though, I have some full shots and medium shots where I can't position lights as close to the subjects and background as I need to get a proper exposure. How do you think I can solve the exposure problem in those cases?

I must add the walls in location are very dark, being it a wooden cabin.

I have some full shots and medium shots where I can't position lights as close to the subjects as I need to get a proper exposure, without using 800 ISO. How can I solve lighting in this cases?