The Vickers Patholette Microscope

A look at an unconventional British microscope from the 1960's. 

Plus some thoughts concerning its design

By Paul James, UK

 
Vickers Instruments Ltd. England, made a number of microscopes of varying designs from simple student stands to more sophisticated professional models, of which the metallurgic and large photoplan forms are still to be found today. This article is about the "Patholette" which is a little sister to the "Patholux", a biological stand made about 40 years ago.

As can be seen from the photo's above, the stand is unusual, though its general overall form was a deliberate design feature to provide a quality portable 'scope and hence the name 'Patholette'. Seemingly to suggest that it was capable of being used in the 'field for pathological work. It originally had a plastic 'dome' cover, but these tended to be broken and are rarely seen today.

It is not the most elegant of stands it must be said, but it has much to commend it, and if I were to only have one 'scope, this model would be very near the top of the list for a number of reasons which I will elaborate on below.

General design

The principle difference between this stand and most others can be seen instantly, as it lacks a traditional limb. In fact the 'limb' and 'foot' are included in one casting, such that the whole stand is rigid and relatively light, though it is by no means 'lightweight'. 

Trinocular version. Also showing

lamphouse and power supply

It functions as a typical binocular compound microscope, with electrically powered illumination, substage and mechanical stage. Both mechanical stage and substage adjustments are executed using co-axial controls, conveniently positioned. The substage condenser can be focussed by simple rack operation.

The base is circular and houses the focusing mechanism, and the light mirror/electric lamphouse source is placed in the central depression in this circular base.

Interesting elements of design

Stage

The key feature of design that I appreciate is that the stage/substage assembly is housed in a well engineered roller/ballrace unit, which moves very smoothly in the main casting via nicely made 'roller slides'. Thus the stage is effectively rigid, yet with minimal overhang. The roller/ballrace contacts are almost as wide as the stage itself, providing high lateral stability yet very delicately controlled by the focussing unit inside the base.

The actual stage surface has ample proportions, and has a very durable black finish which in my example was virtually unmarked. 

Simple stage design with uncluttered finish 
Focussing Unit

Now we are getting to the heart of this microscope design. The focussing unit, which is a very old concept, is in my opinion superior in many categories to the traditional methods of coarse and fine focussing found on all classes of the instrument.

The principle used is based on the old screw lever found in many very old 19th Century microscopes. And having used it I can vouch for its sensitivity and practicality :- 

In the Patholette design the essential principle is the same, but it is a little more sophisticated, and allows both fine and coarse focussing to be accomplished in one co-axial unit. 
Cam follower Pivot Stop Lever tip Ball race guide
The photo's above tell the story...........the bronze worm wheel is the coarse focus and acts through the 'calliper follower' and pivot to support and adjust the height of the stage assembly. The fine focus displaces the whole of bronze unit by a direct acting fine screw thread not visible in the photo's. The mechanism might look a little basic, but its simplicity and sound engineering promise smoothness and reliability, and having too the property of not stiffening up which most traditional coarse focussing can fall prey to.

The movement is finally transmitted to the stage carrier unit via a 'leg' which supports an adjustable stop. The whole lever assembly is self tensioned through gravity, so there can never be any slackness , and thus will function perfectly and almost indefinitely so long as there is gravity!

Mechanical stage 

Stage controls Focus controls condenser focus

Stage roller guides

This co-axial unit is well engineered and is a delight to use, causing minimum disturbance to focussing at the higher powers. I thoroughly like the slide clamp design which is commendably simple yet slide introduction and removal is easily executed. It has more than ample overall movement for the normal 3"x1" slide, and the clamp plate can be quickly released to allow for the examination of larger specimens/dishes etc..

Substage

This is a normal 39mm RMS supporting unit which has moderate focussing travel, and in the mount that I possess is an achromatic 1.25 NA condenser optic housed with iris control. There is provision for centralising this condenser using the two adjusting screws, and this works well, though the amount of movement is limited somewhat, but should be sufficient for most purposes. A darkground condenser was manufactured, but I have not seen this particular design.

Illumination

Standard illumination is electrically powered, but my particular Patholette came without the standard electric illumination lamphouse, so I improvised temporarily using an old mirror. A DIY lamp house and 90 degree prism assembly is a job for me to do this winter.

Optics

The objective changer can support 4 lenses, and this particular instrument came with some flatfield, and standard achromats, and a pair of x 7.5 B&L eyepieces.

The general standard of optical performance in the Patholette is good and certainly more than adequate for normal use. Vickers manufactured and supplied either standard achromat objectives, or achromat 'Micro plan', which have a flatter field; the latter are of good quality and compare quite favourably with European makers of that same period. They also supplied fluorite, and phase objectives.

The binocular head functions well, being easily adjusted for interocular distance. The left eyepiece holder can be focussed independently to provide for dioptric variations. At the base of the binocular, the makers have inserted a negative optical element to presumably alter the emerging rays of light to suit the 160mm tube length standard? I suspect this design is susceptible to knocks causing misalignment of internal prisms which are held by 'nipping' screws. A potential purchaser should be aware of this.

Summary

This microscope is a very interesting instrument with some novel features such as the lever focussing, with convenient placement of the co-axial controls for both the focussing and mechanical stage. It is portable, compact, and rigid as well as being stable, and the operation of the controls is quite intuitive .

There is however one particular feature which could lead to potential damage to the objectives or more likely the slide when the instrument is picked up. Since there is no obvious lifting point for the hand to grasp easily , it is entirely likely that the stage, which is free to move, can be drawn upwards against the slide or objective. Theoretically speaking this should not happen if the stage stop* has been properly set and tightened as it would have been done when leaving the maker. Those of you who might purchase this model should be aware of this, and always make sure no slide is in place if the instrument is handled bodily. 

Some individuals might find this design not to their taste, but I have found the Vickers Patholette has much to recommend it.
 
  
Photo's taken with Nikon Coolpix 800 digicam
All comments to the author Comments to the author sent via our contacts page quoting page url plus : ('pjames','')">Paul James are welcomed.

Microscopy UK Front Page
Micscape Magazine
Article Library


© Microscopy UK or their contributors.

Published in the  December 2001 edition of Micscape Magazine.

Please report any Web problems or offer general comments to the Micscape Editor,
via the contact on current Micscape Index.

Micscape is the on-line monthly magazine of the Microscopy UK web
site at Microscopy-UK


© Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.