The Auxiliary Microscope / PhaseTelescope

A short note on a useful device no longer in production

By Paul James (uk)

Last month's article concerning diy phase telescopes prompted me to write this short article about an old device made by R.&J Beck which has the title "Auxiliary Microscope" printed around the eyepiece's face rim. It could have been used as a separate low power microscope held in a suitable stand, but it seemed that having a 23.2mm body diameter, its true purpose was to slip into the draw tube of the compound microscope, where it could function in two ways :-

With the objective removed from the turret,the auxiliary 'scope can be focussed on the stage below it. The image above shows the auxiliary 'scope in situ in place of the eyepiece and in this position can yield a total amplification of around x6-10 depending on the height of the limb and the position of the eyepiece of the auxiliary 'scope. The field of view is restricted somewhat but is sufficient for most purposes.

Below, the objective from the auxiliary 'scope is seen removed to illustrate the possibility of mounting it instead into the bottom of the draw tube itself, which combined with the original eyepiece would do the same job as Beck's auxiliary 'scope.

The idea behind the auxiliary 'scope I would imagine is that it does not require that the drawtube be withdrawn to attach a low power objective, but just that it replaces the microscope's eyepiece as a phase 'scope does. The use of the bottom end of the drawtube to house longer focal length objectives is a very old idea. Here below we can see that the drawtube from the compound monocular carries an RMS objective thread to take a low power objective like the one from the auxiliary scope.

The image below shows the Beck's auxiliary 'scopes objective screwed in place in the bottom end of the compound microscope's drawtube. Though this particular objective is 50mm even lower powers can be used to advantage providing of course that their physical diameter is less than the draw tube for obvious reasons !

This facility therefore presents itself to be used with low power objectives which could not be focussed when mounted traditionally in the turret. Since the draw tube as shown above or auxiliary 'scope rests higher than the turret above the stage much lower powers can be accommodated.

The great advantage of the Beck auxiliary 'scope is that it can perform not only the job of an extra low power 'scope resting in the eye piece tube, but also as a phase telescope as well. In the latter mode its ability to image the back of the objective/annulus is second to none, and its long smoothly operating eyepiece allows for focussing on any part of the optical train throughout the whole microscope.

A very useful device indeed, yet the idea seems to have faded in modern times? However a little ingenuity on behalf of a monocular microscope owner could result in a useful 'auxiliary/phase microscope/telescope combination ??

All comments welcome by the author Paul James

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