Final answer:
The customary near working distance for the eye to form a clear image is typically assumed to be 25 cm, although it may vary depending on the individual's occupation or age.
Step-by-step explanation:
The customary near working distance, which is the nearest point an object can be placed so that the eye can form a clear image on the retina, can generally be assumed to be 25 cm. This distance is considered the near point of the eye for someone with normal vision, meaning they can see objects clearly at distances from 25 cm to infinitely far away. However, this distance can vary based on a person's occupation, like jewelers who may work at closer distances, or may change with age as the near point may increase due to reduced flexibility of the eye's lens.
For instance, when an object is held 25.0 cm from a person's eyes, the spectacle lens is designed to produce an image at the near point, which is typically 1.00 m away. The image will then be placed 98.5 cm from the spectacle lens, given that the lens is 1.50 cm from the eyes. Furthermore, the lens-to-retina distance, which is essential for clear vision, is usually around 2.00 cm unless stated otherwise in specific circumstances.