A common aid to vision is an ordinary low power pocket lens of magnifying power in the range of × 2 to
× 10. The range of optical devices for the effective study of positions inaccessible to the eye is steadily
increasing. Some using mirrors and lenses (e.g. intrascopes, borescopes) have been established for many
years; others such as light guides and miniature television cameras are more recent developments. All can
be very effective when appropriately used.