I know that the depth of field will be deepened when you narrow the iris of the lens, but I can not explain in detail why it will happen. When narrowing down the iris of the lens, only the allowable range becomes wider when the focus is in place, and strictly the focus is only one plane. Even without knowing its principle, I can take pictures.
Photo taken with f1.4.
ｺﾒﾝﾄをする