When a photographer decides to use flash, it typically starts something like this. Photographer posts online asking which flash to buy, gets a lot of responses, and buys a flash of some sort. They go and shoot with it, and are then disappointed with the look of hard light. So, the next logical step is to post online again asking “Which modifier should I get?”.
The problem is, it’s not that simple. We’ve no idea what look you want to go for. It’s something only you can decide yourself. Your vision is your vision, not ours. But without seeing what they all do, knowing what to get is impossible. So, have a watch of this video from Jay P. Morgan at The Slanted Lens. Jay goes through a whole series of different modifiers to show what they do to the light falling on your subject.