IMHO, the lack of a modelling lamp is the biggest drawback of speedlights for studio work. When you're new to it, it's pretty much vital and will speed your learning with decent results almost immediately. You'll see the 'quality' of the light, know where the shadows fall, avoid difficult reflections, be able to position reflectors easily and accurately. A bright modelling light, when used quite close, will also close down the iris of the subject's eyes to show the colour rather than a black hole that's the hallmark of most flash portraiture. Head-shot specialists often use high-end continuous lights for this reason, but they're very expensive, big and cumbersome. Another thought, if you're into shallow depth-of-field portraits with say an f/1.4 lens, then most studio heads won't turn down low enough for correct exposure, but a decent modelling light is often enough just by itself (if not ideal
).
Also with speedlights:
- slow recycle times, as they'll mostly be at full power. Expressions are fleeting and change very rapidly. When the moment comes, you need to shoot fast. With young kids, you may only get one chance.
- speedlights have just enough power for solo portraits and couples, but run out of puff for groups.
- on the other hand, speedlights are small and light, and you can put them anywhere. They work well with studio heads for things like backgrounds or hair/accent lights when their downsides can be worked around.
ps Studio heads are not expensive. Good quality ones start at around £100, eg Godox or Lencarta.