Compound achromatic microscope




United Kingdom


S.S. Ross / London / No. 8051



Optical 1


Optical 2


Size of the box (h x b x d)

31.7 × 12.6 × 16 cm

Size of the microscope (h x b x d)

29.5 × 8.2 × 12.3 cm

Inventory number

SM 27


The microscope has a brass horseshoe foot with a double pillar between which the limb with the stage can be swivelled. Coarse adjustment is by rack and pinion, there is a draw tube. Fine adjustment by micrometer screw acting on the limb. The microscope has a simple stage with spring clips, there is a condenser with an iris diaphragm, on a short fixed arm in a bracket the concave and flat mirror.
The eyepiece was not investigated.
There are two objective lenses in a rotating nosepiece, both signed ‘Ross London’, one is a ‘2/3’ with serial number 23264, the second one is a ‘1/6’ with serial number 23239.
They were measured using the Bleeker microscope, the ‘2/3’ with a 10× Huygenian eyepiece, the ‘1/6’ with a 5× Huygenian eyepiece.

Objective 2/3 1/6
Focal length (mm) 17.72 4.07
Magnification 82 211
Numerical aperture 0.27 0.66
Resolving power (µm) 2 < 1

The ‘2/3’ is a bit astigmatic, using a standard 0.17 mm cover glass it shows spherical undercorrection.
The ‘1/6’ is a bit astigmatic as well, the field of view is flat, it is spherically well corrected. The diatom Pleurosigma angulatum is resolved into lines.

It is unknown who S.S. Ross was. He was probably a middleman who used the famous name of Ross to sell his microscopes for a better price.