The type of your shadow is so important with flash photography, and there’s an easy way to learn how to change that shadow type: just check out the Slideshare below.
If you’re impatient though, here’s a quick rule of thumb:
The larger your light source is, the softer the shadow will be. Now, this doesn’t mean ONLY just the ruler measurement size of the light, because the SUN is obviously bigger than the earth, but since it’s so far away it’s just a small point in the sky, we would call it a small light source.
So let me try that again:
The larger your light source is in relation to your subject, the softer the shadow will be. If you put a tiny light RIGHT UP NEAR your subject, it takes up more space in the subject’s vicinity, so it would “become” a larger light source in relation to your subject.
Want to understand more about it? Here’s the Slideshare: