A slim well made case makes for a neat appearance, you can imagine many of these sat side by side along laboratory benches in the mornings ready for all the students to arrive, quick release catches makes handling straightforward although caution must be used pulling the case clear not to snag on any parts of the microscope. This one is labeled No.81 so part of a large consignment.

The above photograph shows a close up of the under stage and base, the large field lens which can house square colour or polar filters easily comes off on locating pins which for transport by post makes it a necessity to tape it down or remove and pack, this one wasn't and could have caused much damage in transit to objectives or paintwork, thankfully it didn't! The lever on the left of the base actuates a swing in auxiliary lens for the Kohler system for objectives 20x - 100x. The knob on the right of the base actuates the field diaphragm similar to some Leitz and Leica designs. A centering sub stage houses the condenser, note the two rings on the condenser, the top is for all dry objectives, the bottom for oil immersion. It is unusual and unlike Zeiss in that the condenser iris is still in the light path at all times and must be adjusted to suit for phase operation. There are 'blank' positions in upper and lower disks to allow for correct setting for each objective range. Just below the centering screws there is the rather narrow condenser diaphragm control, although large in diameter I found this not as convenient as those with a long arm, the latter easier to adjust and grip, especially when the control is partly hidden in normal operation. The slots at the edge of the base are to accept hand rests which are missing on this stand.

Note the substantial aluminum coarse focus controls which are based on standard rack and pinion in operation, these actuate on the stage not the limb. The fine focus system is 'sprung' to allow for wear take up and provides excellent 'feel' at all magnifications. The condenser is not 'quick release' like many microscopes although can be removed if required, the idea being you specified the desired condenser from Watson when ordering. They made a simple 2 element Abbe, 5 element achromatic shown [option of long working distance] and an oil immersion zonal dark field to be used with 90x or 100x objectives whose apertures have been reduced to NA of 1.0 using stops although this could be used for circular oblique illumination.

Watson say in their literature that the achromatic NA 0.9 is perfectly adequate for their oil immersion objectives. It is very well corrected for both spherical and chromatic aberrations. Small Allen key points set the centering of the phase annuli, [the phase outfit would originally have contained a small hex adjuster missing here], on this stand no adjustment was required. No filter tray is supplied with the achromatic condenser which prevents much experimentation with home made Rheinberg, circular oblique or other contrast techniques. Oblique illumination can be still applied by offsetting the brightfield port on the condenser, or movement of an opaque card say on the field lens and circular oblique on the 40x objective by using the 100x phase annuli whilst dark-field can be applied to the 10x objective using the same technique.

A close up of the condenser and unassuming 'Para' phase objectives, a simple 'short' 5x 'Para' is also included in the set which is not shown here and on this sample needed an extending collar to make it roughly par-focal with the rest of the range. The phase range shown are 10x NA 0.28, 40x NA 0.70 and oil immersion 90x NA 1.30, the extra NA compared to many typical phase achromats provides a crisp clean look to phase with reduced 'shadowing' at the edges of prepared diatoms and little colour abnormalities.

The 7x compensating eyepieces should be used with objectives 20x and above and none compensating Huygenian below this, this is verified in taking photographs using a Sony P200. With the binocular head 1.5x factor this together with the supplied eyepieces gives 10x overall magnification. Watson did 'field' tests between parallel tube binocular and inclined binocular tubes asking how much strain the users had over continued use, the result was that most preferred the inclined so this was adopted.

The objective line up for the System 70 are 8 Parachromatic, 2 Planpara, 3 Fluorite and 3 Apochromatics with 7 phase variants so a good number to choose from. The Parachromatic 5x is reasonably plan whilst all of the phase objectives tested here give bright detailed images, my favourites being the 40x using circular oblique illumination [see later] with green or pale blue light and the 90x phase which gives excellent results. A total of 18 different eyepieces were available!

The 6 volt 30 watt bulb comes in two types, clear and slightly frosted, the latter is designed for phase use where any filament abnormalities in the light path where reduced, my stand you can still see residual filament 'lines' in the field of view clearly picked up by camera, so only a partial success? This is as true to original Kohler you will find in any microscope and puts some modern research stands to shame pertaining to be of 'Kohler' design one of which I know has not one but two strong in line diffusers permanently in the light path.. however, the use of diffusers in the light path reflects the wide field of view eyepieces of today and small filament area of halogen bulbs compared to custom made tungsten bulbs and narrower field of view eyepieces of older designs.

The only diffusion is on the phase bulb and then if you order the clear version through the whole light path there are no diffusers. This has to be highly commended and shows how well Watson implemented the source illumination and condenser, it is pretty obvious the optics have been well chosen and researched. Remember there is no swing out element on the condenser only an auxiliary lens in the base for objectives above 20x. The ceramic bulb holder is pre-centered at the factory and collar on the bulb provides accurate centering within the holder, sadly on this one the solder had deteriorated and the collar had to be re-made. A rather fiddly metal plate holds the bulb securely in place acting against strong sprung bulb electrical contacts.

A simple clean design in the base, the lever operated control on the left half way up is for the swing out auxiliary lens and in the center, the large drum operated by chord similar to design from 1960's transistor table radios is for the field iris, this has plenty of leaves although in use at high magnifications where the aperture is very small looks rather 'ragged' in the field of view. The large housing at the top holds the substantial mirror reflecting the light source up through the field lens attached on the top panel. All the metal work is substantial, well finished and simple in operation which should give many years of life. The Kohler base uses a total of 4 optical elements with the auxiliary lens in situ. The bulb is mounted in a bayonet fitting on the base back plate allowing easy bulb replacement without removing the base.

Other none Kohler variations are the mains voltage illumination base with 25 watt 100-120v or 200-250v ac diffused light and the low voltage base with 6v 18 watt bulb with rheostat built into the base.

The power unit normally rests via a large locating pin onto the top of the limb, I am not certain I like this but least it keeps all the parts together! It doesn't come much simpler with a rheostat and a rather quaint moving iron ac meter. The toggle switch for the 240 v ac mains can be seen on top together with the 3 way special socket to accept the mains, a rather inconvenient location I thought with the lead drooping down. The short thick cable seen at the top takes the variable low voltage to the bulb in the base. Laboratory instructions have been left on being part of its history! The unit is very easy to work on as shown below.

Underside of power supply, very simple operation with mains transformer feeding a good quality ceramic based rheostat with the meter indicating the working volts. This one had a modification to prevent operation above 6v by using a large wire wound resistor soldered in line with the rheostat to prevent bulbs being blown.. I guess by possible careless operators. This has been removed and restored to the original condition. Occasionally it is desirable to overdrive the bulb by a small percentage specially for high power phase. The rheostat turns were dirty as shown here causing fluctuations in light intensity but after a clean this was improved somewhat but not completely.

This is the add on X Y control which can be retrofitted to plain stage with clips. It is attached by 3 large bolts with Allen key heads, although Watson describe this as an innovative design I came to dislike it with a passion when trying to refurbish it. As received the X control was lumpy and the Y control a rather frightening 'jump' to the right of objects occurred at anything above 10x. Whilst the rest of the microscope is well finished this didn't look up to the same standards being rather crude. It does prevent the typical protrusion you get from a rack and pinion design and I guess the wooden case gave Watson a 'headache' with its close fit when being brought down to be clipped to the base so the rack and pinion design was probably ruled out.

Here it shows the unit before being refurbished, it comes apart fairly easy, 2 screw heads can be seen on the horizontal X shaft these are the 'stops' to prevent too much travel. The mechanism relies on a friction coupled metal 'tape' running around a rotating rubber guide [hidden on the left] and the other end a 'sprung' rotating brass guide, seen above right, this gives the tension. The problem is the metal tape if removed has a tendency to twine itself in knots, is easily creased, flimsy and hard to work with. The friction if too loose between the brass X drive shaft and the rubber guide [there is no anchorage it is just a push on fit] leaves the X control stranded some where along its travel so any muck or oil that has creeped in could cause problems, I had to dismantle and clean. The springy copper alloy fingers holding the brass guide seen on the right above had to be re-tensioned which caused all sorts of problems. After spending hours of frustration I finally managed to get a working unit and all the work paid off with both the X and Y smooth in operation but for such a simple system it is very annoying to work on. I didn't dismantle the Y control working as best as I could cleaning parts in situ. Even this gave me a headache as there is control to set the angle of the slide carrier to prevent binding and scraping of the stage and is a combination of a metal plate with two screws and nylon adjustable grub screw but I got there in the end!

A few images are shown below, the first, a crop of a human flea taken with the 5x objective using a hand held Sony P200 digital camera at the eyepiece.

The remaining three are two types of diatoms from a Klaus Kemp 8 form test plate [Stauroneis phoenocenteron and Navicula lyra] using a 1.3Mp Opticstar CCD camera in place of the eyepiece. Good detail and considering the Para's are not described as plan objectives give a competent flat field image. No additional sharpening has been applied post re-sizing.