Compound achromatic microscope

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.

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.

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.