DOF (Depth of field)

In optics, particularly as it relates to film and photography, depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image.

85mm lens with f1.8 give you shallow DOF

We use many examples to talk about DOF using different aperture size to control the depth of field.

More importantly, I will say choosing different focal length of the lens is more important, since the aperture you can control all depends on the sun light. Unless you have the studio to control the light source, in reality, you can just select a wider lens will shoot more.

14mm wide lens, you can see object clear at the front to the back.