三さん重じゅう焦しょう点てん

Meanings

1

noun

trifocal

Technical term used in optics, photography, and lens design to describe a system with three focal points.

spot, point, mark

二に重じゅう焦しょう点てん
二重焦点 means bifocal (two focal points), while 三重焦点 means trifocal (three focal points).
焦しょう点てん
焦点 is the general term for focal point or focus; 三重焦点 specifies three such points.

Compound of 三重 (さんじゅう, 'triple') and 焦点 (しょうてん, 'focal point').