The available light was coming from my left so I decided that a softbox would best replicate the quality of light that was there. I have a two foot (60cm) x three foot (90cm) Chimera softbox so I fitted it to a Lumedyne head and placed it on a lighting stand about six feet to the subject's right at about 20 degrees above his eye level.
The flash reading at 50 joules was f4 so I put the power up to 100 joules and settled for f5.6. The spread of the softened flash was such that the whole width of the scene was fairly evenly lit, but I decided to allow some of the available light to contribute to the overall exposure. With the camera set to 1/45th of a second and the lens to f5.6 the ambient exposure was two stops under, so I set the shutter speed to 1/30th which is one and a half stops under exposed - enough to add something to the scene without risking camera shake.
The LCD screen confirmed all of my light meter readings so I shot with a 70-200 f2.8 lens with variations on the composition and some vertical and horizontal frames. Then, with the subject filling the same portion of the frame I switched to a 17-35 f2.8 lens giving a quite different perspective. On balance I preferred the longer lens composition, but I went on to shoot a few more locations and lighting situations. The keyword for this kind of lighting is subtlety. It is a way of taking something that is so very nearly perfect and bringing it that little bit nearer still to that goal.