Glossary

Information-oriented. Quick definitions, English and German.

Several of these terms are habitually confused because they sound alike — object distance vs image distance, real vs virtual, focal point vs focal plane. They're grouped so you can see the contrast directly.

Rays and lenses

English	Deutsch	Meaning (school-level)
Ray (of light)	Lichtstrahl	An arrow along which light travels in a straight line — the basic model of geometrical optics.
Optical axis	optische Achse	The centre line through all lenses. Everything is aligned to it; misalignment is the #1 error source.
Refraction	Brechung	Light changing direction at a glass surface. What lenses are made of.
Converging lens	Sammellinse	Thicker in the middle; bundles parallel rays into a real focus. Also: positive/convex lens.
Diverging lens	Zerstreuungslinse	Thinner in the middle; spreads parallel rays as if from a virtual focus. Also: negative/concave lens.
Focal point (F)	Brennpunkt	The point where rays parallel to the axis meet after a converging lens.
Focal length (f)	Brennweite	Distance from lens to focal point, in mm. Printed on every CoreBox lens holder.
Focal plane	Brennebene	The plane through the focal point, perpendicular to the axis.
Optical power (dioptre)	Brechkraft (Dioptrie)	1/f with f in metres. The glasses-prescription number.
Thin lens	dünne Linse	The simplification that a lens is a single bending plane, fully described by f.

Images

English	Deutsch	Meaning
Object distance (g)	Gegenstandsweite	Distance object → lens plane.
Image distance (b)	Bildweite	Distance lens plane → image.
Lens equation	Linsengleichung	$1/f = 1/g + 1/b$ — connects the three lengths.
Real image	reelles Bild	Rays actually meet: an image you can catch on a screen. Always inverted.
Virtual image	virtuelles Bild	Rays only seem to come from it; visible by eye, never on a screen. Upright.
Magnification (M)	Vergrößerung	How much larger the image is — as a length ratio ($b/g$) or an angle ratio (telescope).
Intermediate image	Zwischenbild	The real image inside a telescope or microscope that the eyepiece magnifies again.
Inverted / upright	umgekehrt / aufrecht	Upside-down (real images) vs right-way-up (virtual images).

Instruments

English	Deutsch	Meaning
Magnifier / loupe	Lupe	A single converging lens with the object inside f. $M = 250\,\text{mm}/f$.
Projector	Projektor	Lens with the object just outside f: enlarged real image on a screen.
Objective	Objektiv	The lens facing the object — in telescopes and microscopes the first, most critical stage.
Eyepiece / ocular	Okular	The lens facing the eye; a magnifier for the intermediate image.
Galilean telescope	Galilei-Fernrohr	Converging objective + diverging eyepiece: upright, compact, small field.
Kepler telescope	Kepler-Fernrohr	Two converging lenses: inverted image, real intermediate image, astronomy standard.
Tube lens	Tubuslinse	In infinity microscopes: the lens that focuses the parallel bundle into the intermediate image.
Tube length	Tubuslänge	Finite optics: the fixed objective→image distance (DIN: 160 mm, printed on the barrel).
Finite / infinity-corrected	Endlich-/Unendlich-Optik	Whether the objective forms the image directly (finite) or first sends rays parallel (infinity).
Infinity space	Unendlichraum	The parallel-ray region between infinity objective and tube lens — where filters go.
Condenser	Kondensor	Lens that concentrates illumination onto the sample.
Köhler illumination	Köhler-Beleuchtung	Illumination setup imaging the light source away from the sample plane → even lighting.
Darkfield	Dunkelfeld	Illumination so oblique that only scattered light enters the objective: bright sample, black background.

Microscope-specific

English	Deutsch	Meaning
Numerical aperture (NA)	numerische Apertur	Sine of the half-angle of the accepted light cone. Sets resolution — not magnification.
Resolution (limit)	Auflösung(sgrenze)	Smallest distinguishable detail: $d \approx \lambda / (2\,\text{NA})$.
Empty magnification	leere Vergrößerung	Magnifying beyond the NA-limit: bigger, but no new detail.
Working distance	Arbeitsabstand	Free space between objective front and sample when focused.
Exit pupil	Austrittspupille	The small bright disc above the eyepiece where all rays pass — put your eye (or phone camera) exactly there.
Field of view	Sichtfeld / Sehfeld	The area you can see at once; shrinks as magnification grows.
RMS thread	RMS-Gewinde	The standard microscope-objective screw thread (also on the Z-stage).
Ramsden eyepiece	Ramsden-Okular	Eyepiece from two identical plano-convex lenses; flatter field than a single lens.
Accommodation / autofocus	Akkommodation / Autofokus	The eye's (the phone's) ability to refocus at different distances.

Errors you will actually see

English	Deutsch	Meaning
Chromatic aberration	Farbfehler / chromatische Aberration	Blue focuses shorter than red → colour fringes at edges.
Spherical aberration	sphärische Aberration	Edge rays focus shorter than centre rays → can't be sharp everywhere. Reduced by correct lens orientation.
Vignetting	Vignettierung	Darkening towards the image corners — usually a pupil/aperture mismatch.
Astigmatism (tilt)	Astigmatismus	Smearing in one direction — often a tilted lens insert in UC2 builds.

Related

• Parts and parameters
• Wave-optics terms (interference, diffraction, coherence…): HoloBox glossary