Most of it is just the shape of the eye (spherical with a concave cornea),
the final fine focus is an opposing set of muscles which distort the shape of the lens.
A poet's eye would focus.
the lens
When an object is placed very close to our eye, the eye muscles can't adjust quickly enough to focus on the object, leading to a blurred image. This is because the lens in the eye needs to change shape to focus on objects at different distances, which takes time.
by moving and looking at it
the retina
pupil
No, to focus ligh, muscles in the eye change the length and thickness of the lens.
The pupil or cornea
Independent focus in binoculars means that each eyepiece can be adjusted separately to achieve sharp focus, allowing users with different vision in each eye to customize the focus to suit their needs. This feature is particularly useful for individuals who require prescription eyewear or have unequal vision in each eye.
When you focus on nearby objects, the lens of your eye becomes thicker. This adjustment is necessary to bring the image of the object into clear focus on the retina, which is located at the back of the eye.
The lens of the eye helps to focus images on the retina by changing its shape and thickness. This process, known as accommodation, allows the eye to adjust and bring objects into clear focus based on their distance from the eye.
Keep your eye on it and focus