Definition

1. Adjective:
   • Bifocal: Describes an optical system, typically a lens, that has two distinct focal points or focal lengths. This allows for clear vision at two different distances, most commonly for near and far vision.

Usage Examples

• Adjective:
  • Ông ấy đeo kính song tiêu để đọc sách và nhìn xa. (He wears bifocal glasses to read books and see far away.)
  • Thấu kính song tiêu được thiết kế với hai phần quang học khác nhau. (A bifocal lens is designed with two different optical sections.)

Advanced Usage

• Technical/Physics Context: The term is primarily used in physics and optics. It precisely describes a lens property and is not typically used in metaphorical or abstract contexts.
  • Hệ thống quang học song tiêu được ứng dụng trong kính thiên văn. (A bifocal optical system is applied in telescopes.)

Variants and Related Words

• Kính song tiêu / Tròng kính song tiêu (n): Bifocal glasses / Bifocal lenses. This is the most common compound form, referring to the physical eyeglasses or lenses.
• Đa tiêu (adj): Multifocal. A related term for lenses with more than two focal points (e.g., progressive lenses).
• Đơn tiêu (adj): Single-vision. A related term for lenses with only one focal length.

Synonyms

• Hai tiêu điểm (adj phrase): Having two focal points. This is a descriptive phrase rather than a direct technical synonym.

Notes on Meaning

• Specificity: "Song tiêu" is a specialized technical term. In everyday conversation, people are more likely to refer to "kính hai tròng" (two-part lenses) or simply "kính đọc sách có phần nhìn xa" (reading glasses with a part for distance) to describe bifocal glasses, though "kính song tiêu" remains the correct technical term.

1. (vật lý) Bifocal