What is the best technique to soften a hard shadow created by an oblique flash?

To soften a hard shadow created by an oblique flash, bouncing the flash from a reflective surface is the most effective technique. When light is bounced, it disperses over a larger area, creating a more diffuse illumination. This diffusion helps minimize the starkness of shadows, resulting in softer, more flattering lighting conditions on the subject.

Bouncing the flash can be done by directing it towards a wall, ceiling, or any reflective material nearby, which acts as a diffuser. The angle and distance from the surface will also affect the quality of light and the resulting shadows—the further the flash is from the surface, the softer the shadow will become, as the light will spread out more.

Increasing the flash intensity would not help in softening the shadow; it may actually make it harsher, while a color filter would change the hue of the light without affecting the shadow quality. Moving the flash further away could help with light spread but is not as effective for directly softening shadows as using a bounce technique. Therefore, using a reflective surface for bouncing the flash provides the most visually pleasing outcome in terms of shadow softness.