This is useful when refining the focus beyond the hyperfocal distance, ie focusing between the HFD and when the focus distance reaches infinity.
In this focusing zone the far DoF is meaningless, as the far DoF distance is infinity. But the infinity defocus blur in this zone still has meaning, as represented by the blur gauge on the right hand side of the focus bar.
The four sensible choices that are available to calculate the near DoF are:
- The defocus blur alone, ie the green/red vertical bar
- Twice the defocus blur alone
- The defocus and diffraction blur taken in quadrature, ie the total blur
- Twice the defocus and diffraction blur taken in quadrature
Finally, the bottom DoF info shows the defocus blur at the near and far DoFs, and updates to show the infinity defocus component if in the infinity focus mode.