The quality of shadow is determined by two elements – the size and the shape of the modifier used, and the distance between your light source and your subject. You can quickly change both elements (and therefore, the characteristics of your shadows) by moving either closer or further away from your subject/light source.
This means that once you have an idea of the type of shadow you are aiming for, the answer to “what lights should I use?” can be determined by considering what movements you will make before taking your final shot.
If the shadows are round and diffuse, then move close to your subject. If they are harsh, angular or sharp, consider moving further away to see what happens.
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