Corrección óptica que enfoca tres longitudes de onda (rojo, verde, azul) en el mismo plano focal, eliminando casi por completo la aberración cromática. Distintivo de las ópticas de cine de gama alta, marcadas como APO.
Apochromatic (APO) refers to a lens design that brings three wavelengths of light—red, green, and blue—to the same focal plane. Simple lenses focus each color slightly differently because glass refracts short-wavelength light more strongly than long-wavelength light. An achromatic design corrects two wavelengths; an apochromatic design goes a step further and captures the third as well. This is made possible by special glasses with anomalous partial dispersion, such as fluorite elements, combined with a carefully tuned lens calculation.
Why it matters on set
Chromatic aberration appears as colored fringes on contrast edges—a branch against a bright sky, a chrome trim in backlight, highlights on water. When viewed in 4K or 8K on the big screen, these fringes are immediately noticeable, and in post-production, they can only be corrected to a limited extent because the color information at the edge is already blurred. APO-corrected optics deliver clean edges directly in the negative or recording—this is why cine lens manufacturers prominently advertise this designation.
Distinction and Limitations
APO is not a protected term, and strictly speaking, the correction only applies to the center of the image and specific focus distances. Longitudinal chromatic aberration (color fringes in front of and behind the plane of focus, visible in the bokeh) and lateral chromatic aberration towards the edge of the image behave differently—a lens can be perfectly corrected in the center and still show fringes at the edge. If you rely on the abbreviation, you should still test: place highlights slightly out of focus and check for magenta and green fringes.
- When testing lenses, specifically film contrast edges in backlight—that's where the correction shows up first.
- Also check out-of-focus areas: longitudinal chromatic aberrations live in the bokeh, not in the plane of focus.
- APO correction makes optics heavier and more expensive—for a deliberately soft vintage look, an uncorrected lens might be the better choice.
Términos relacionados
Cuestionario
1. Was beschreibt „Apochromatisch" am besten?
2. Zu welchem Department gehört „Apochromatisch"?