PENTAX DA 21mm f/3.2 AL Limited

US 7,411,746 B2 Embodiment 1 — Hoya / Kato & Saori

8 elements / 5 groups
f = 21.60 mm design; 21 mm nominal
F3.2 marketed; F3.3 patent design
68° diagonal production field
1 hybrid aspherical surface
Two-group floating focus

Focus Mechanism

Two-group floating focus: front group and rear group move objectward by unequal amounts.

Optical Elements (9)

ElementTypeGlass
L1Positive MeniscusS-LAL14 (OHARA equivalent)
L2Negative MeniscusS-LAH65V (OHARA equivalent)
L3Negative MeniscusS-LAH66 (OHARA equivalent)
L4Positive Meniscus / Near Plano-ConvexS-TIM35 (OHARA equivalent)
L5Positive MeniscusS-LAL18 (OHARA equivalent)
L6Plano-Concave NegativeS-TIH13 (OHARA equivalent)
L7Plano-Convex PositiveS-BSM15 (OHARA equivalent)
L8rAspheric Resin LayerCompound UV-curing resin (patent; no catalog glass match)
L8Positive MeniscusS-LAH66 (OHARA equivalent)

Analysis

Detailed analysis available in the interactive viewer above.