Compound achromatic microscope




United Kingdom


Henry Crouch / London / 7353



Optical 1


Optical 2


Size of the box (h x b x d)

15.6 × 30.8 × 18.7 cm

Size of the microscope (h x b x d)

29 × 13.8 × 18 cm

Inventory number

SM 7


In box with lock.
This is a simpler version of the microscope described under SM 5, coarse adjustment is only by means of a sliding tube in a sleeve. Fine adjustment is by a micrometer screw acting on the limb.
There is one Huygenian eyepiece, its focal length is 27.8 mm, its magnification is 9×.
There are two objectives, ‘2/3’ and ‚1/6’, provided with the standard RMS thread. 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) 15.57 3.55
Magnification 47.7 243
Numerical aperture 0.15 0.64
Resolving power (µm) 2.5 < 0.8

Objective ‘2/3’ is still in good condition, the results of the star test are good, even its contrast is well defined. Objective ‘1/6’ is not in such a good condition anymore, there is a fault in the cement between two of its lenses. As a result the contrast of the image is not very good and the diffraction rings are not circular. With a Möller diatom test the image is a bit hazy. Stauroneis phoenicenteron is resolved into dots, it is possible that the objective could resolve Pleurosigma angulatum as well when in good condition.

See also SM 5.