Promaster Universal Softbox (best flash diffuser rating: 8.57) for hot shoe flashes is a high quality flash diffuser. As the name suggests, it fits virtually any flash and can be used on- and off-camera. The unit folds flat and easily fits into most gear bags.
Many portable flash light modifiers utilize Velcro straps to attach to the flash. Promaster, however, takes a slightly different route. Instead of a simple Velcro strap, Promaster Universal Softbox comes with an attachment base. The base mounts onto a flash head with a stretchy strap, which applies tension to the head for secure attachment. The softbox itself mounts onto the base with Velcro. Please note that the base is not flat or collapsible, but it is small enough, so it doesn't really affect portability.
 |
 |
 |
 |
The following images show how the mounting base fits onto the smaller head of Nikon Speedlight SB-600 (left) and the larger head of Canon Speedlite 580EX II.
 |
 |
The included instructions suggest to install the base first and then attach the softbox. We find that it may actually be more convenient to fully assemble the unit first and then mount it on a flash. This, however, can be a matter of personal preference.
 |
 |
Promaster Universal Softbox, similarly to its little brother Promaster Softbox for pop-up flash, features mirror-like lining to reduce the light loss. It also has a grid-like reflector at the center of the front diffusing panel, which according to our tests, does a good job of diminishing the hot spot.
With any speedlight softbox, we recommend using the manual flash zoom mode and setting the flash zoom to a value optimal for a particular diffuser. For Promaster Universal Softbox, we suggest using 24mm flash zoom setting (or the widest one available on your flash). We do not recommend using a pull-out wide angle diffusing panel, as our testing shows that the mirrors inside the softbox may produce some weird reflections significantly degrading the light quality. The image below shows the light distribution pattern at 24mm flash zoom.
 |
The following images give you an idea of how effective Promaster Universal Softbox is for close range portraits. The flash was placed about 2 feet from the subject. The left image was taken using unmodified direct flash, while the right one was produced by the Promaster Softbox.
 |
 |
One of the main competitors of Promaster Universal Softbox is LumiQuest Softbox, which is white-lined. The image below compares the sizes of these two units.
 |
We've taken sample shots with both softboxes to see the difference in light quality. In both examples, the flash was set to the same manual output and 24mm zoom setting. (We actually prefer using LumiQuest Softbox with the flash zoom set to 14mm, but that wouldn't be a fair comparison).
 |
 |
The shadows produces by LumiQuest Softbox (left image) appear to be softer than the shadows in the Promaster Universal Softbox image (right). The Promaster diffuser, however, has the edge in light efficiency. Our measurements show that LumiQuest modifier loses about half a stop more in this setup, which means that Promaster unit delivers longer flash battery life and a better shooting range.
Besides the close range portraits, Promaster Universal Softbox also works great for macro and, in general, any close up photography (food, product, etc.). The next image is a tabletop photography example. The flash was set within one foot from the pot.
 |
In conclusion, Promaster Universal Softbox is a quality product that is easy to use. It features an original mounting base that ensures secure attachment to the flash. The softbox works great for a wide range of close up applications. It is portable and can be easily stored in virtually any gear bag. The mirror-like lining of Promaster Universal Softbox makes the images look somewhat harsher compared to competition, but it makes up for that by being more light efficient and saving flash battery power.
