Coming back from a brief photography sabbatical, I've found quite a few posts on the forum regarding qualities that would make a camera considered professional vs. a camera considered non-professional. But that got me thinking, what is it that makes a camera a professional camera? Is it build quality? Is it megapixels or the size of the sensor? Is it a monetary figure that one must cross, or is it a camera that can perform in any situation even though most of those situations won't be experienced by the owner? I'm under the current believe that if you are making money on what you do, then the tool is a professional tool whether it is a 1Dx or a 110 film camera. I'd like to pose the question to the forum here. What are your opinions?