How are we able to manually change our eye focus on demand, when most of the time it happens automatically?

Question

How are we able to manually change our eye focus on demand, when most of the time it happens automatically?

In: 5

Answer 1

If you don’t need any glasses, the distance will be sharp and hard to get blurry.

As object get closer we need to adjust (create plus) to get the light on our retina. On 40 cm we need about +2.50 diopters.
We do that with the muscles around our eye and change the lens in our eye. Since you can relax muscles, you can let go of the adjustment. You can also play around and focus on non existing objects.

But you will notice that it will be very hard to do that in distance, unless you are hypermetropic (need a plus prescription for distance).

My eye related technical English isn’t perfect. Sorry.