How Softbox Size Effect Soft Light
On this video tutorial photographer Gavin Hoey takes a look at a number of different softboxes and how each of hem influence the quality of light and the resulting image.
The larger the light source the softer the light (typically). On this video Hoey demonstrates how this basic knowledge translates into real world images. He tests several different light modifiers of different sizes and also talks about the reason one might need a huge light modifier (usually to take full body images and to be able to place your light source further away, so it will not be seen in the shot).