A quick follow up on Speedlights And The Shirt. I know too much of the shirt - last thing. Next time it's shoes or something. Actually it's a pretty good exercise to make something so ratty look kinda halfway decent in a photo. It's really easy to do the reverse - namely making something nice look like crap. Moving on…
A fellow photo nut case asked me about the fill ratio when doing something like this and was wondering if I could show a visual of what more fill might look like. It just so happens that I have one that is about 2/3 to 1 stop more fill than the image in the original post. I mentioned that you could probably go even another 2/3 or even a whole stop more than this shot. When going for this kind of feel that is about my limit. Up to a point it will make it look a bit more glow-y but as soon as you cross a very fine line it will cease to look glow-y and start getting flatter and flatter. Try it yourself - it's easy enough.
One suggestion. No matter how you deal with the key hard source that is simulating the sun. If you are experimenting with fill ratios set that flash to manual and build it up slowly maybe taking a shot without the key - just the fill and then a shot of both so that you can get a technical and visual reference to what looks like what. I think you might be surprised at how little fill goes a long long way. You will know when you are at the too much point. Pretty much the whole ambience will evaporate.
If you happen to be doing this during the day then just use ambient light for the fill as long as the sun is not actually shining on your subject it should be pretty easy to get a wide range of fill ratios indoors from black to as much as you want. Just remember that Aperture and ISO will send the flash and the ambient up where shutter speed will control the ambient level only.
In my experience getting the fill to look right along with understanding how to keep light off stuff in the image is the biggest stumbling block to people with strobes of any kind and why a lot of photographers "only do natural light". The trick is making it look like situations you really do like shooting in and then making it even better. Putting light everywhere is pretty easy and in most cases is not what you want.