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Compound achromatic microscope

Maker

ROBBINS

Country

USA

Signature

Alfred Robbins Co. / Chicago

Category

Microscopes

Optical 1

Compound

Optical 2

Achromatic

Size of the box (h x b x d)

33.5 × 17.5 × 10.5 cm

Size of the microscope (h x b x d)

30.5 × 8.5 × 17 cm

Inventory number

SM 6

Description

With the microscope goes its original wooden box with a brass grip.
There is a black lacquered U-shaped foot, on which a short brass pillar is mounted, the limb with the table hinges in a slit in this pillar. Below the round table is a revolving stop and a mirror in a bracket. The limb carries a micrometer screw for fine adjustment and coarse adjustment is by means of rack and pinion. There is a draw tube as well.
There is a Huygenian eyepiece, the focal length is 28.85 mm, the magnification is 8.67×.
There is a revolving nosepiece carrying two objectives, ‘2/3’ and ‘1/6’, the thread used is the standard RMS type. Both were investigated using the Bleeker microscope with a 160 mm body tube and a 5× Huygenian eyepiece.

Objective lens 2/3 1/6
Focal length (mm) 20.6 4.4
Magnification 39.4 202
Numerical aperture 0.2 0.6
Resolving power (µm) 2 0.8

Objective lens ‘2/3’ shows some astigmatism. Objective lens ‘1/6’ is chromatically not very well corrected, the contrast of the image is bad, it is under-corrected for spherical aberration, the diffraction rings are irregularly shaped. The diatom Stauroneis phoenicenteron is resolved into dots.

It is not yet clear whether Robbins actually made the instrument or just was the middelman.