Cooke M4000 ‘Nuclear’ microscope

Stephen Parker

Exhibited is a Cooke, Troughton & Simms (CTS) M4000 ‘Universal’ microscope equipped for the analysis of nuclear emission tracks in photographic film. It was made in the early 1950s.

This is to continue the CTS theme introduced by Robert Ratford and his VPM!

The M4000 was designed to allow both transmitted and incident light microscopy. Like many contemporary microscopes it was clearly inspired by the Leitz Ortholux (introduced in 1937), but has a number of refinements. It is more solidly built, therefore more resistant to vibration, and – most importantly – has the trade-mark fine focussing of the CTS range, operating on the nosepiece only. The latter is a joy to use, and – as it is lightly loaded – affords a good degree of crash prevention between objective and slide. Originally the M4000 was provided with two 6v 48w lamps (as opposed to the Ortholux’s 30w) in focussing lamp houses. This contrasted with the first version of the Ortholux which had one lamp house with a switchable mirror to direct the light either to the transmitted or incident light paths. Later Ortholuxes, however, changed to two lamphouses (thus allowing greater intensity for incident light). Strangely, later models of the M4000 went the other way and switched to a single lamphouse with switchable light paths. I think this was to facilitate the use of alternative light sources for fluorescence work (a dual lamphouse – mercury & tungsten – was available to fit in the lighting port). For photomicrography, a special bellows camera was used on a pole which fitted onto the top of the limb. The trinocular head has a first surface mirror which switches out of the way to allow a prism-free direct light path to the camera.

The adaptions for nuclear research are–

  • A special X/Y measuring stage using micrometers subdivided to 5 microns with a range of movement of 25mm in each direction; and
  • A goniometer eyepiece for measuring angles.

(Measurement in the Z direction is by the divided fine focus control.)

In 1964 a later model M4000, so equipped, cost £650 without optics – £13,513 in today’s money. (The average male weekly pay was £17 12s in that year.)

For more general use, the stage movement by micrometer can be a bit slow, though there is an a second, faster, Y movement fitted (which was included to allow the whole width of the film to be scanned).

A photograph of the later version of this microscope (with one lamp) is at page 187 of the exhibited book, “Microscope Design and Construction” by B. O. Payne. At p. 186 is a photograph of the kind of film that the microscope was used to analyse.

This particular microscope was purchased from Vaughn & Ven Dodge (well known past members) at the first (2005) Microscopium. It had, in turn, been exhibited by them at the 1991 Quekex. (So there is a 30th anniversary here …). A copy of their accompanying text, as recorded at page 14 in the Winter 1991 (18th) issue of the Quekett Bulletin, is shown. In it, they describe having rescued the microscope from the bin in a very sorry state. They then explain the steps they took to restore it to its former glory.

When I bought it, it was usable for incident light but not complete. It was fitted with a Watson incident light unit that was not properly in alignment with the lamp due to an incorrect light spacer being used. I have managed over the years to source the correct transmitted nosepiece and the correct spacer to use CTS incident light units. I also found the goniometer eyepiece (which had been missing). Other bits picked up (but not exhibited) include phase equipment and a macro tube and lenses. So far, I have left the Dodge’s lighting arrangements in place. I am not altogether sure that the incident light path originally had the currently fitted (rather elaborate) filter housing (including space for a water trough); rather a simpler lamp may have been fitted, similar to the one used on the later model of the microscope. The Dodges adapted the lamphouse to take 6v 18w bulbs in place of the original 48w.

For the analysis of nuclear emission tracks, the transmitted light nosepiece would have been used with high power (probably oil immersion) lenses. Today I have fitted a Cooke Universal nosepiece with an incident light brightfield/darkfield lens. (Alternatively, the nosepiece can be fitted with metallurgical or transmitted light objectives, in the case of higher powers being the tips of standard Cooke objectives unscrewed from their bodies and mounted in special holders to maintain tube length.)

Shown under the microscope are, alternately, an uncovered coal section plus various metal specimens. Incident light is an excellent way of viewing the former. A modern Chinese inspection camera is used to show the output on a monitor, blending old with new!

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