Los Angeles, Feb 20 : Veteran Hollywood star Helen Mirren felt like a "deer in the headlights" in her early career because she had "no idea" how to behave in front of the camera and hadn't grasped the "fundamentals" of filmmaking. She admitted to Britain's OK! magazine: "I was utterly useless at the beginning as I had no idea about getting in the shot or the frame of the camera or what to do when you are in the frame. "I felt when I started out in film it was like deer in the headlights acting. It was like, 'Action!' then, 'Freeze!'. I did not know what to do. It took me a long time. "I did a film called 'Excalibur' once and none of us had an idea of what we were doing. We didn't realise we couldn't change the shot and we had to do what we rehearsed. Even those fundamentals I did not understand." The 76-year-old actress is keen to go back to work in the theatre because she loves the "challenge" but said getting back on stage is getting more "difficult" as she's getting older, reports femalefirst.co.uk. She said: "I try to go back to the stage every few years but it gets difficult as you get older. "It's only two or three hours a night but you work from the minute you wake up in the morning, as everything is geared towards that moment. "It's like, 'When do I eat and when I do rest?' It's a challenge, like, 'Can I do it still? Am I capable?' "There's a sense of challenge and a sense of duty as there's a slight leftover of, 'Well that is real acting' and film is something else. "That's not true but it's a very different kind of energy and commitment. So it's a combination of these things." Mirren knows if she gets a stage offer, she will find it hard to turn down. She added: "I'm lucky I've got to a point where if I'm asked to play a role on stage it's a great role. I find it hard to say no to great roles." /IANS