I am so in tune with @Nada and completely agree with him in every respect. The airbrush is just a tool, that much is true, but so is a palette knife when painting using oils, to which I also enjoy. The thing for me is that being able to paint perfect facsimiles from a photo gives me the ability to use those same techniques to produce the same effects in my own compositions. I appreciate that the majority of you artists are highly skilled and far better than me at painting portraits from photos, but I prefer the challenge of actually painting something that hasn't already been done ie a photo or other piece of art. That being said, at the moment I have spent quite a few hours composing a painting for which there is no photo or other reference in existence. I did however use various references to draw from.