Visual Echoes makes a slick, but odd looking devise that extends the working range of your accessory flash unit via a “Fresnel screen” placed at a fixed distance from the flash head. Although the “Fresnel screen” is made from flimsy plastic, it really does work, but there are some limitations you should know about.
There are several sizes to choose from. As it needs to be strapped down hard and aligned with the flash head fairly accurately, it’s important to get one that fits your flash unit size. In this test I used the FX-1/1B medium size because it fits the Sony HVL-F42AM. If you have the larger Sony HVL-F56AM or F58AM, (or other brands) you need to get a larger size.
Warning: do not look back through the fresnel lens while busting a full power flash pop or it might be the last thing you ever see!