×

Compound achromatic travelling microscope

Year/Period

1870-1890

Maker

UNKNOWN

Country

United Kingdom

Signature

Unsigned

Category

Microscopes

Optical 1

Compound

Optical 2

Achromatic

Size of the box (h x w x d)

8 × 28.5 × 12 cm

Size of the microscope (h x w x d)

27 × 22.2 × 18 cm

Inventory number

SM 25

Description

The microscope is kept in a wooden box with some green baize linings.
This travelling microscope is after a design by William Moginie, who worked for the firm of C. Baker. Coarse adjustment is by means of the body tube running in a collar. This collar is connected to one of the three rods forming the stand. Fine adjustment is by means of a micrometer screw in the rod to which the collar is connected. There are a flat and concave mirror adjustable in a bracket. There is a simple stage.
The microscope has a Huygenian eyepiece with a focal length of 41.1 mm and a magnification of 6.1×.

With this microscope are three objective lenses:

  • A ‘1/5’, signed ‘Patent Ross London no. 20140’ with correction collar for ‘dry’ and ‘wet’ (water immersion).
  • An unsigned objective lens in a box signed ‘J.H. Steward / 406 Strand’ 2’’.
  • an objective lens signed ‘J. Swift en Son / London’ 1’’.

 

Objective lenses 1/5 dry 1/5 wet 1 inch 2 inch
Focal length (mm) 5.84 5.23 21.6 38.7
Magnification 190.6 214.7 41.8 21.9
Numerical aperture 0.81 0.88 0.2 0.09
Resolving power (µm) < 0.8 < 0.8 1.75 3.75

 

The field of the ‘1/5’ objective lens is strongly curved, there is spherical overcorrection, the shape of the diffraction rings is irregular. When used with a 15× Huygenian eyepiece the diatom Pleurosigma angulatum is resolved into dots (‘dry’). Using water immersion (‘wet’) the lines of the diatom Surirella gemma are just not resolved.
The 1-inch objective lens shows a trace of astigmatism. The other objective lens is just good.

Accessories: a live box with spring rings.