Nearly every fashion and portrait photography has a beauty dish in their studio, or at least they should. This modifier is a classic because it produces a quality of light somewhere between that of a softbox and a standard reflector, basically giving photographers the best of both worlds when it comes to portraiture. It has an odd design to thank for this—it features a parabolic reflector with a deflector plate right in front of the light to bounce the light around the dish's surface evenly. By doing this, it can control the direction of the light and create a harder, more focused light with a dramatic but smooth falloff from the highlights into the shadows. By doing this, your subjects will have added definition, making it easier to show off distinct features, and still have a pleasing softer shadow quality, signatures of the wraparound lighting effect photographers desire.
That is a basic overview of what a beauty dish does, but it is far from everything this modifier can do. As with all light sources, a little bit of knowledge and the occasional accessory can result in huge differences in your final product. One easy way to do this is simply by moving it closer or farther away from your subject. By placing the light closer, the light will become much softer, though it won't have any of the hot spots that you might get with a traditional softbox. And, though falloff into the shadows will be a little softer, it will maintain that crisp look. Obviously, you will have the opposite effect if you move the light farther away—then you will get a harder light with a quicker falloff. Another change you can make comes before purchase, since you will need to decide between a white interior and a silver interior. Luckily, this is quite simple, because the white interior produces a softer look and the silver creates slightly more contrast.
If you want to mix things up even more, you should look for some accessories, namely grids and diffusion. Grids do the same thing here that they do on other lights: narrow the beam angle and reduce spill. Beauty dishes already have good control over spill due to their parabolic shape, but a grid will certainly focus the beam angle down to an even tighter spread. At the opposite end is a diffuser, usually in the form of a "sock." This will simply soften the light more, giving you effectively the same look that you would get from a softbox, but with no central hot spot, and a circular catchlight. This leads to another characteristic of dishes—they can create very natural and pleasing catch-lights in your subjects' eyes, something small but important in portraiture. Finally, some models have interchangeable deflector plates, allowing you to add some warmth with a gold plate, extra softness with white, or even use a translucent plate to purposefully create a hot spot.
A neat aspect of some newer models is the collapsible design. Profoto's latest 24" OCF Beauty Dishes offer this, allowing them to be stored and transported more easily. Standard dishes can be cumbersome if you need to travel with them; they take up a lot of space and may require their own dedicated cases to keep them safe, so these collapsible designs are a lot more practical, even if they aren't going to have as "perfect" a shape as a standard dish. However, if you aren't going to need to travel much, the standard options are going to create a better light.
Hopefully, you have a better understanding of how this specialized modifier works and how you can make it work best for you. Any questions on specific models or how it might compare to other modifiers? Let us know in the Comments section, below!