Hello everyone,
I need cloudlike objects with no definite boundary .Think for example of a spherical cloud that is very dense et the center and that becomes gradually dilute(and therefore more and more transparent) when the distance from the center increases. 
 
I looked at the totorial of the candle ligt with a spherical diffuse light around the flare. It is similar to  what I need but it is done with  a spot light reflecting on a spherical surface. Therefore it has the desired apperarance for me only if one views  it from the opposite.  But what I need is a cloud-like-object that looks as  a cloud-like-object from any angel of the camera.