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Compound achromatic microscope, ‘stand 3’

Maker

SEIBERT

Country

Germany

Signature

SEIBERT / IN / WETZLAR

Category

Microscopes

Optical 1

Compound

Optical 2

Achromatic

Size of the box (h x b x d)

42 × 17 × 20 cm

Size of the microscope (h x b x d)

30.6 × 10.3 × 18 cm

Inventory number

SM 28

Description

The microscope goes with its original wooden box.
It is entirely built from brass, with the usual horseshoe foot with a short pillar. The microscope can be inclined between trunnions, there is a clamp. The microscope has a circular stage which can be centred, below a Abbe type condenser with a focal length of 8.4 mm. On a fixed arm a concave and a flat mirror in a bracket. Coarse adjustment by rack and pinion, fine adjustment by means of a micrometer screw acting on the limb. The microscope has an adjustable draw tube, the tube length can be varied between 15 and 19 cm.
There are three Huygenian eyepieces, ‘0’, ‘I’ and ‘III’, their focal lengths and magnifications are:

Eyepiece 0 I III
Focal length (mm) 49.37 34.86 21.64
Magnification 5.06 7.17 11.55

 

There are three objective lenses, ‘I’, ‘III’ and ‘V’, they were investigated using the Bleeker microscope with a 170 mm body tube. Number ‘I’ with a 10× Huygenian eyepiece, the two others with a 5× Huygenian eyepiece.

Objective I III V
Focal length (mm) 23.14 10.99 3.40
Magnification 68.9 118.08 275.5
Numerical aperture 0.21 0.50 0.81
Resolving power (µm) 2 1.25 < 1

Objective ‘I’ is slightly astigmatic, for the rest it is well corrected.
Objective ‘III’ is well corrected, the diatom Navicula lyra is resolved into lines.
Objective ‘V’ is well corrected. One of its lenses is damaged, as a result the diffraction rings are irregularly shaped and its contrast is not very good anymore. It still resolves the diatom Stauroneis phoenicenteron into dots and Pleurosigma angulatum into lines.