Optical Size

A design variation within a
Type Family
that optimizes letterforms for a specific rendering size, compensating for the optical effects that occur when type is scaled. At small sizes (caption or footnote), optical-size masters feature heavier hairlines, wider
Counter
, more open
Aperture
, and increased
X-Height
to preserve
Legibility
; at large sizes (display or poster), masters can afford finer hairlines, tighter spacing, and more delicate detail. In
Variable Font
, optical size is a registered axis (opsz) that can be adjusted continuously, and modern
CSS
supports automatic optical sizing via font-optical-sizing.