Gray Render Problem

Hi, I’m trying to render a scene and both with rendered preview and with cycles render the result is a gray picture. When doing it with the preview, the first samples are black and white and then it blends into gray. Why is this happening?

Can you attach or post a link to an example blend file

I found out that it has something to do with the camera settings, something that I’ve changed, because with a default camera it works okay, that may be a big clue, anyway I’ll be posting the .blend file in some hours