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
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
Heurck'. All the models have a tripod stand which is
light, rigid and very stable and in my opinion superior to the
horseshoe design and is normally finished in black whilst the body
controls and other smaller components are finished in a beautiful
deep golden lacquer, the quality of mechanics, finish and choice of
just as good on the cheapest Fram as on the Van Heurck. Most of the
mechanical sliding surfaces have sprung wear adjusters including the
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 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
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.
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
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
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
and 1/12th" are in use.
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,
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.
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
Objectives Supplied with the
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
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
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
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.
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
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
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
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.
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.
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
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. 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.
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.
Central part of Gyrosigma
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
was on the back focal plane and removed effectively.
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.
Bee wing mounted by Mike Samworth.
Watson & Sons 1" objective, acceptable field flatness considering
100% coverage by the camera.
Old and faint transverse section of Elder mounted by Richard Suter.
Watson & Sons 1" objective, 100% coverage by the camera.
Yellow Sage, a section through flower buds mounted by Biosil.
Watson & Sons 1/2" objective, good detail capture aided by above
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.
P. Koristka 1/12th" oil immersion objective, much better seen visually.
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
this superb stand.
Further reading and for comparisons: A
Personal Review of a Smith & Beck microscope ca 1856.
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