A softbox and an umbrella are both popular diffuser options for a speedlight. Both have their own unique features and benefits that make them suitable for different types of photography. The choice between the two ultimately depends on the specific requirements of the photographer and the shoot.
A softbox is a rectangular or square shaped device that diffuses light from the speedlight by reflecting it off of the interior walls of the box and through a translucent front panel. Softboxes are often favored by portrait photographers because they produce a soft, even light that minimizes harsh shadows and is well-suited for close-up shots. Softboxes also typically have more reflective surface area than umbrellas, making them more effective at spreading light and achieving a softer, more diffused look.
An umbrella, on the other hand, is a collapsible device that consists of a metal or plastic frame covered by a translucent or reflective material. Umbrellas can be used to diffuse light from the speedlight by positioning it between the light source and the subject. Umbrellas are often favored by event photographers because they are lightweight and portable, making them easy to carry from one location to another. Umbrellas are also generally easier to set up and take down than softboxes, making them a convenient option for on-the-go shoots.
In conclusion, a softbox is better for photographers who need a large, even source of diffused light, while an umbrella is better for photographers who need a portable and quick-to-set-up diffuser. A source such as "The Photographer's Guide to Lighting" by Syl Arena highlights the advantages and disadvantages of each option in detail. Ultimately, the best diffuser for a speedlight will depend on the specific needs of the photographer and the type of shoot they are undertaking.