Optics of a "modern" compound microscope: The Ernst Leitz achromatic compound microscope

Summary information

• Calculated total magnification w/ 10x eyepiece: – Low objective (#1): 170x = 17x objective – Medium objective (#2): 232x = 23x objective • Resolution –17x objective = 0.9 µm –23x objective = 0.6 µm • Aberration – Chromatic Aberration: Minimal • Greater for eyepieces than the objective lenses • n550 – n660 in the order of 10exp3 for eyepieces and 10exp4 for objectives – Seidel Aberrations: Almost none

Ray tracing optical path

Chromatic aberration

Lens f(g)-f(w) µm f(r)-f(w) µm E1 391 260 E2 334 81 O1 -22 -14 O2 -50 -60

Individual lenses have large chromatic aberration, especially the eyepieces (left). (How they determined this.)

E: eyepiece; O: objective Positive length indicates a shorter focal length

focal length mm % difference White 8.51 NA Red 8.53 0.24 Green 8.54 0.30

The combination of all lenses in the optical path results in very low aberration.

Color fringes

The difference in working distance of objective "2" with different illumination color

Resolution Sample objective #1

Calculated magnification = 170x (17x objective) Approximated = 164x (16x objective)

E1 E2 O1 O2 focal length (mm) 13.7 31.7 26.7 12.7 Diameter 12 20 9.3 6.4 S(o) 13.7 -22.9 31.8 8.5 S(i) - 13.3 165.9 -25.8 Magnification 18.5 0.6 3.0 -5.2

Comparison between the 1905 Leitz (top) and modern (bottom) compound microscope. Both near 200x magnification. Note how the modern microscope resolves the hairs. Left: Fly wing; Right: micrometer scale (10µm).

Approximating magnification

1/5/10