Introduction.

The idea of this article is not so much to provide detailed facts or figures on the microscope but more importantly a 'hands-on' approach using a brass microscope 100 years old next year and to see how it performs with some references compared to a modern stand. The Watson Edinburgh Stand 'H' was a highly successful microscope for Watson & Sons having a long manufacturing period starting from 1892 and in the 18th Edition 1906 catalogue was priced at 15.00 for the stand, two objectives, Abbe condenser and mahogany case. The final version I have seen illustrated of much later vintage was an all black lacquered version with just the controls in natural lacquer.

I have owned this previously well used Watson Edinburgh 'H' microscope since April this year and have had the chance to use it on many occasions and I have been impressed with both the mechanics and optics. My first venture into brass microscopes was an early Smith & Beck ca 1856 and although I enjoyed using it I quickly found the lack of condenser a big drawback and I sold it some time after writing an article about it in Micscape. Since my aim is to use these microscopes regularly on a day to day basis rather than sitting in a display cabinet, the Smith & Beck had to fulfill my requirements but using it with higher power objectives without a condenser was hopeless, the microscopists in those days must have been using auxiliary bulls-eye lenses I didn't have or using techniques to illuminate their slides which are more difficult to accomplish now than they were at the time.





Part of the Watson Range.


The Edinburgh shares similar features to the smaller 'Fram' together with a larger version of the Edinburgh called the 'Royal' and flagship model the famous and imposing 'Van Heurck'. All the models have a tripod stand which is light, rigid and very stable and in my opinion superior to the continental horseshoe design and is normally finished in black whilst the body tube, controls and other smaller components are finished in a beautiful deep golden lacquer, the quality of mechanics, finish and choice of optics remain just as good on the cheapest Fram as on the Van Heurck. Most of the mechanical sliding surfaces have sprung wear adjusters including the course focus and 'X' 'Y' stage controls allowing slack to be taken up with small adjusting screws even after 100 years use. The Edinburgh is a compact microscope measuring only 13" tall in a typical angled position increasing another 2 1/2" with the draw tube fully extended.


The Stand.




Fig 1.

The camera does not do justice to the microscope in Fig 1. the lacquer is in particularly fine condition on the tube and controls. A draw tube is available to allow adjustment from just below 155mm all the way up to 235mm allowing a range of English and Continental optics to be fitted and some degree of varying magnification with low power objectives. The three position nosepiece fitted here has a tight friction fit plus nice positive action and par-centrality between low and high power objectives is good. The stand was also available with a two or four position nosepiece with aluminium components being used in the construction as an option in the catalogue of 1906, whilst a rotating stage could also be ordered for petrographic work but these are not commonly found today.





Fig2.

In Fig 2. the 'X' 'Y' controls can clearly be seen and with the large diameter controls give a rapid but smooth positioning of the subject on the stage which also includes take-up wear adjustments. The 'swinging' mirror can be moved some way off centrality to allow oblique effects but I leave it central and use accessories fitted to the sub-stage filter tray, the mirror can also be moved up and down by a small amount possibly when used with very low power objectives like the 4" allowing focusing of the concave side of the mirror with the condenser swung out of position.

The condenser maybe swung out of position since it rotates about one fixing screw whilst another fixes it tightly into place if required. The course focus adjustment is by standard rack and pinion with over sized controls making adjustment very light and precise, it is so well balanced that the up or down motion feels virtually identical and I don't use the fine focus with regularity until higher power objectives like the 1/8th" and 1/12th" are in use.

Fine Focus mechanism.

Of particular note is the fine focus mechanism using a milled head affixed to a fine screw this acts on a long lever with the pivot point close to the body tube, the surfaces of all the main parts are hardened and polished providing a very precise mechanism even using the 1/12th" oil immersion objective, the reactionary force is supplied by a long spring running closely parallel to the sliding surfaces of the fine focus. The design was so successful that it was used for many years without alteration and the adjustment had a finer pitch than several of the continental designs especially in the earlier years of manufacture.





Close-Up of Stage and Sub-stage.




Fig 3.


A close-up picture of the stage and centrable sub-stage Abbe condenser can be seen in Fig 3. Reflections make the black parts brighter than they are in reality and again, take-up wear adjustment is available on the rackwork of the condenser allowing light and smooth operation. The colour of the body tube is more accurate in this picture being taken in a different room from the first two and the colour balance much warmer. My objectives are not parfocal so a certain amount of care must be taken not to damage front elements of objectives or slides but I quickly got used to allowing enough clearance going from medium to high power. The Abbe condenser does a reasonable job of providing enough numerical aperture for most objectives [aplanatic cone of NA 0.5] but with high power oil immersion objectives like my 1/12th" Apochromatic it is far from ideal but Watson did supply at extra cost a superb 5 element condenser called the Universal Condenser which had an aplanatic cone of NA 0.95 [with top lens removed 0.40] and a 6 element Holoscopic oil immersion condenser costing 6 15s in 1906 for critical work providing an aplanatic cone of 1.25 under oiled conditions neither of which came with the stand. There is one omission on the stand which would make it more usable and that is a quick release lever for the angle of body tube which is a friction fit and very stiff but some Edinburgh's seem to have this fitted depending on vintage.





Objectives Supplied with the Microscope.




Fig 4.

Supplied as standard with microscope shown in Fig 4. are from left to right, [magnifications for 160mm tube length], a 1" [6x NA 0.21], 1/2" [13x NA 0.34] and 1/6th" [42x NA 0.74] parachromatics. The parachromatics also seen in catalogues with the name simply shortened to 'para' were one step up from the basic Argus range from Watson, above these were the Holos objectives requiring matching Holos eyepieces and apochromats to be used with either compensating or Holos eyepieces but never the less these optics are good with bright contrasty images aided by the simple monocular design of the microscope and one interesting point is the lack of thickening and soft edge definition when looking at diatom type slides with the 1/2" objective that often accompanies modern 10x NA0.25 achromats, instead, crisp edges not unlike those from Wild's high NA phase fluorites are seen which is most pleasing.

The 1"objective provides a reasonably flat field but as you go further up in magnification the field flatness and highest resolution becomes more localized to the centre where the subject should always be placed for best image quality in these older design of lenses, Pleurosigma angulatum is quite easily resolved with the 1/6th" but is very dependent on the quality and brightness of the illuminating source for the microscope and provided better results when fitted to a Russian LOMO stand with aplanatic condenser and external LOMO filament lamp with field iris. The parachromatic objectives provide best contrast with their aperture reduced to 65-75% using the Abbe condenser unlike many modern computer designed objectives with special lens coatings which provide optimum contrast and resolution with the condenser set at 90-95% of their full aperture. The objectives and cases are beautifully made, heavily lacquered and miniature works of art in their own right.

The Watson Catalogue of 1906 is rather confusing since they have reverted to stating magnifications for the older 10" tube length [image distance of 10"] so the 1" objective is stated as a 12x, the 1/2" 20x and the 1/6th" 65x but the Watson Edinburgh is primarily being used at 160mm tube length and would require the draw tube fully extended to obtain these magnifications which I think very unlikely so why they continued to quote them like this I don't know. The magnifications change again somewhat for the same objectives in a later condensed book 'The Book of the Watson microscope'  so whether the design of each objective was changed I don't know but from my experiments the figures given in the main paragraph above are reasonably accurate and agree with the later book. Using low to medium power objectives the draw tube was a convenient way of continually changing the magnification without changing the eyepiece and quite a lot of  leeway was possible without due problems but this is not the case as you approach 1/8th" and oil immersion objectives where the correct tube length should be strictly adhered to.

Additional High Power Optics used with the Microscope.




Fig 5.


Additional objectives I use with the Watson are a 1/12th"Apochromatic immersion NA 1.30 by P. Koristka, Milan Italy in superb condition with one of the heaviest and finest tooled cases I've seen, again with a deep gold lacquer and a 1/8th" Watson 'para' [51x at 160mm NA 0.87] which is shown in the background of Fig 5. both are of excellent optical quality, the 1/8th" is a later design to that supplied with the microscope. A high quality Beck 8x compensating eyepiece is used with these higher power objectives rather than the simpler 6x and 10x eyepieces supplied. Francesco Koristka as he later became known was originally from Poland and his business had links with Zeiss, if this objective is typical of his output then it is a fine range of optics from the Italian catalogue, this maybe an early sample since he moved from Milan in 1895.





A Simple Illuminator.




Fig 6.

In Fig 6. a simple cold light source is shown using a Jessops fluorescent light box with home made baffles removes glare especially to the unused eye whilst observation is taking place. The light provides a good white balance being designed for slide transparencies and needs no adjustment for luminosity and is supplied with a low voltage DC source from a wall type adapter. Brightness is sufficient from the lowest to highest powers provided the light box is kept close to the microscope and condenser focus is aided by simply holding a pencil point touching the light box illuminating surface and focused with the condenser. True Kohler illumination from a quality external lamp would no doubt improve contrast and edge definition of diatoms at high powers but I find this light source cheap and convenient to use with reduced eye strain which often accompanies critical illumination using high wattage filament bulbs, even so I prefer  observation periods of about 15 minutes followed by a short rest and then resume to reduce fatigue.






Some of the Accessories.




Fig 7.

Fig 7. shows some of the original accessories supplied with microscope including a metal dark-field stop for low power objectives and oblique illumination plate together with their brass case and original polarizer-analyzer which I don't use preferring modern Polaroids fitted to the eyepiece and condenser. Added to these are a set of acetate colour filters I made and my special colour wheel with long actuating arm which can be used with or without dark-field or crossed-polars for special effects and can be rotated easily whilst fitted in the filter tray.





Name plate and Serial Number.




Fig 8.


Fig 8. shows the Watson & Sons inscription and overlay by Wallace Heaton Ltd, London. W1 who supplied the microscope originally to the first purchaser also showing the coat of arms and rather official 'Appointment to his Majesty the King', Suppliers of Photographic Equipment. The fading white lettering of the serial number can be seen just above the nearest foot, 10143 placing it around 1907.





The Mahogany Case.




Fig 9.

A simple mahogany case shown in Fig 9. with lock and key was supplied with the microscope holding the stand and three objectives, polarizers and accessories, some water damage near the bottom panel is evident which thankfully doesn't seem to have affected the microscope maybe because it was outside the box at the time of damage, the original maroon felt is in good condition. Mounting pins for a card holder, the holder itself and the card giving details of objectives and magnifications with the supplied eyepieces is missing from the door.


Condition and Maintenance.

As received the microscope was in very good condition with the natural lacquer in excellent order and although the scope had been used extensively in the past some very small adjustments to the focus, stage and sub-stage adjusters was all that was needed to allow consistent and smooth operation. Some of the lubricants had dried back so this was cleaned off and a trace of new lubricant applied and with this type of design with close machined tolerances much lower viscosity lubricant is needed. The optics were quite dirty and needed a clean and my usual method of using a blower brush to remove abrasive particles and then using photographic cleaning tissue dampened with a little of the supplied cleaning fluid brought them back to excellent working order. Typical for this age of microscope the optics can suffer from fungal attack on the glass elements and indeed the 1/6th" showed quite bad signs of this but fortunately it was on the back focal plane and removed effectively.





Sample Pictures.

The pictures below were taken with a Sony P200 digital camera handheld onto the Watson eyepiece, unfortunately I have no easy way of connecting my camera to the Edinburgh and my patience ran out trying to set up a tripod and get the spacing right between camera and eyepiece. Obviously with slow shutter speeds, optical zoom on the P200 set around 1.5-2x and almost certainly camera shake these are only a fair representation of what is seen visually, however what can be deduced is acceptable field flatness from the 1" objective, good detail and contrast from the 1/2" objective whilst the image of Gyrosigma balticum can only be described as poor compared to visual observation was included to show that the Abbe condenser running full aperture can just about cope with high numerical aperture objectives. As I summarise in the conclusion this is a microscope ideally suited for visual observation and unless an easy method of connecting a camera is found I prefer doing my pencil sketches and drawings. All the images were taken with the Edinburgh illuminated by my modified Jessops light box and the camera set to auto white balance, I like black and white photography so three of them are in this mode.





Fig 10a.

Bee wing mounted by Mike Samworth.

Watson & Sons 1" objective, acceptable field flatness considering 100% coverage by the camera.




Fig 10b.

Old and faint transverse section of Elder mounted by Richard Suter.

Watson & Sons 1" objective, 100% coverage by the camera.




Fig 11a.

Yellow Sage, a section through flower buds mounted by Biosil.

Watson & Sons 1/2" objective, good detail capture aided by above average NA.




Fig 11b.

Foot of a Blow fly mounted by C.M. Topping.

Watson & Sons 1/2" objective, a difficult subject due to the depth and density of the subject.




Fig 12.

Central part of Gyrosigma balticum.

P. Koristka 1/12th" oil immersion objective, much better seen visually.





Conclusion.

The Watson Edinburgh 'H' student microscope is as usable today as it was 100 years ago, the fine mechanics and optics plus ergonomic design are a delight to use and put many modern microscopes to shame. The parachromatic objectives which normally come with the stand are of good numerical aperture providing bright crisp images with all subject matter including botanical sections and specially diatom strews and type slides. I recently purchased a large number of mixed diatom slides and this microscope has been used throughout to make my usual notes on subject matter and provide the images for making my small pencil sketches to go with the slides. I don't think its forte is for photographic use where modern plan objectives are more useful but if the main use is for visual pleasure of subjects down the microscope together with admiration of a finely crafted instrument it is a sound investment and highly recommended.


Recommended reading: Brian Johnston's article in Micscape The Watson "Mint" metallurgical microscope with excellent images and facts of this superb stand.

Further reading and for comparisons: A Personal Review of a Smith & Beck microscope ca 1856.


Comments to the author, Ian Walker, are welcomed.

 

 

Microscopy UK Front Page
Micscape Magazine
Article Library


Microscopy UK or their contributors.

Published in the January 2006 edition of Micscape.

Please report any Web problems or offer general comments to the Micscape Editor .

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 .