These oculi resemble large monocles, ranging from 1′ in diameter to as large as 12′ in diameter. They are made of an alchemical glass and shaped to focus area of effect spells into a beam with length dependent on the lens. The beam extending from the lens requires a save against breath weapon rather than against spell for the same outcome as the original spell.
These damage multipliers and such assume that the entire lens is contained in the area of effect of the spell. If only a partial lens is contained, consider using a diameter more similar to the area, possibly with further penalties for uncentered coverage.