What is the far point of a person with normal vision?

What is the least distance of distinct vision of a normal human eye (in $cm$)?

What is the other name of long-sightedness?

$(a)$ What is meant by the least distance of distinct vision?
$(b)$ How does the thickness of the eye lens change when we shift our focus from a distant tree to reading a book?

Name the essential parts of the human eye.

$A$ person is able to see objects clearly only when these are lying at distances between $50 \text{ cm}$ and $300 \text{ cm}$ from his eye. Identify the kind of defects of vision he is suffering from. Give reason for your answer.