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Compound achromatic microscope

Maker

BAUSCH & LOMB

Country

USA

Signature

Bausch & Lomb Optical Co. / Rochester / N.Y. / No. 75322

Category

Microscopes

Optical 1

Compound

Optical 2

Achromatic

Size of the box (h x b x d)

36.4 × 17.7 × 22.5 cm

Size of the microscope (h x b x d)

29.6 × 11.3 × 17 cm

Inventory number

SM 9

Description

The microscope is kept in a mahogany box with a nickel-plated grip.
It is a simple student microscope with a black enamelled horseshoe foot, the limb can be inclined. The mirror is on a swing arc, there is a condenser, the stage is covered with a thin sheet of bakelite. Fine focussing by micrometer screw and spring acting on the limb, coarse focussing by rack and pinion. There is a round double (?) objective changer on the body tube.
With the microscope go two Huygenian eyepieces, a ‘5’ and a ‘10’. The eye lens of the strongest eyepiece is badly scratched.

Eyepiece 5 10
Focal length (mm) 50.15 26.45
Magnification 4.98 9.45

There are two objectives, both signed ‘B & L’, one a 16 mm 0.25 NA, the other a 4 mm 0.85 NA. They were investigated using the Bleeker microscope with a 160 mm body tube and a 5× Huygenian eyepiece.

Objective lens 16 mm 4 mm
Focal length (mm) 16.85 4.05
Magnification 49.2 216.5
Numerical aperture 0.22 0.83
Resolving power (µm) 2 < 0.8

The 16 mm objective is in a rather bad shape, the cement of the lenses is cracked, the front surface is scratched. As a result the contrast is moderate and the diffraction rings are not well defined but a bit frayed and there is astigmatism. The field is flat. The objective is spherically under-corrected.
The 4 mm objective is spherically well corrected, there is some coma present, the contrast is again moderate. It resolves the Stauroneis phoenicenteron diatom into dots, Pleurosigma angulatum is resolved into lines.