The 49" Translucent Deep Umbrella from Elinchrom is a very large modifier with a deeper than normal profile that allows you to vary contrast by sliding the lamp head forward and backward along the umbrella shaft to focus or defocus the light output. The depth gives you more directional control of the light.
The umbrella can be used in standard bounce mode, which transmits some of the light through the translucent fabric and raises the ambient light level for a high-key look. You can also turn the umbrella around, aim the convex side at your subject, and "shoot through" it for a crisper look. An optional black diffuser with a silver interior, which is sold separately, slips over the umbrella's open side for controlling light spill.