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Refraction bench · WebGL

# One beam,
bent honestly

No photograph on this screen is doing the work — the prism is being refracted right now, per frame, on your GPU. Drag it. Change the index. The spectrum you see is the same arithmetic lens designers use, minus the glasses.

Index of refraction 1.52
Dispersion (Abbe ↓) 0.18

Drag the prism to rotate · beam is collimated at 632.8 nm reference

L-85 cutaway · 7 elements in 6 groups

## Glass decides
before software does

A lens is a chain of refractions, and every surface answers before any firmware runs. Our L-85 uses two low-dispersion elements to keep the spectrum you just dragged from fanning out across the frame — dispersion corrected in glass, not in a profile.

The cutaway above is a physical section, milled for measurement. Element count and spacing are measured from it, not from the drawing.

## MTF, not adjectives

“Tack sharp” is not a specification. Contrast transfer at given line pairs per millimetre is. These curves are measured on an optical bench at full aperture — sagittal and meridional, out to the corner.

- 10 lp/mm · sagittal
- 10 lp/mm · meridional
- 30 lp/mm · sagittal
- 30 lp/mm · meridional

L-85 · f/1.8 · infinity focus · bench-measured 2026-07

## Specification

L-85 specification — item, value, condition
Item | Value | Condition
--- | --- | ---
Focal length | 85 mm | nominal · ±1.5% at infinity
Aperture | f/1.8 – f/16 | 9-blade · near-circular
Elements | 7 in 6 | 2 LD · measured from cutaway
Close focus | 0.62 m | 1:7.2 magnification
Filter | Ø 62 mm | brass, front-threaded
Weight | 438 g | without caps, with hood

## Bench visits

We measure loaner samples for free and publish the curves — manufacturers welcome or not. Bench time and MTF requests:

bench@lumina.optics