How deep can the aperture be opened to 2.8? Is there any formula to calculate?

Although there are too many complicated parameters involved, there is still a formula to calculate the depth of field.

Calculation formula of depth of field:

Depth of field =(2 times diffusion circle diameter x lens focal length square x aperture value square x focal length square) /(4 times lens focal length d diffusion circle diameter square x aperture value square x focal length square).