Leitz Ortholux Black Enamel Microscope.

...


By Ian Walker.  U.K.



Introduction.

There has been much written over the years about this microscope and in this article I will try to avoid too much duplication of the already thorough articles written in Micscape by Paul James on the Heine condenser, Gregor & Normand Overney's article on Leitz Stands in Black Enamel and the resources supplied by Gordon Couger on his science-info website to name but a few. It is quite possible to assemble substantial documentation on manuals, accessories, optics etc giving the user detailed knowledge on the microscope. Here I give a tour and some hands on thoughts on using the scope perhaps with the aim in mind of giving details that may be of useful to microscopists considering it as their next purchase.

At first glance seen in pictures on the web, brochures or books, the would be purchaser may consider it of large and heavy build, although substantial using a light alloy casting, it is perhaps smaller than one would think measuring 32.5cm (12 3/4") to limb top and 37.5cm (14 3/4") to the centre of the eyepieces on the trinocular head fitted to this stand. Side by side a Zeiss Photomicroscope seems noticeably larger, in fact on some desks or work tops it may need a plinth beneath the base to raise to sufficient height for comfortable viewing.

It also has a relatively small footprint due to its 'T' shaped base allowing low slung controls, although it is quite deep due to the protruding lamp housing at the rear. Provided you are not moving it about many times it can transported short distances with a comfortable grip around the upper limb and support beneath, preferably with the lamp assembly removed.




Schematic of earlier Ortholux with single lamp. Ernst Leitz Wetzlar documentation.

Note the lack of field iris, swing-in auxiliary lens and diverter mirror for epi-illumination. The lens after the lamp filament is frosted.

Three variants of the Ortholux black enamel stand are to be found, the older one dating back to the late 1930's when the Ortholux was introduced, this has a single external lamp house attached to the base the light of which can be directable by lever allowing epi-illumination. With no field diaphragm this is ideally suited to the Berek condenser for routine work.

Later, two ports are situated on the rear of the limb allowing mixed lighting of epi-illumination and transmitted. This can be used as a rough guide to the date of the stand if you have seen one and don't know the serial number. In Gregor & Normand Overney's article on Leitz microscopes of the period they show a version fitted with dual light source in 1960 and later still, dual light source and field diaphragm 1966.

In the 1970's the Ortholux II stand was introduced similar in appearance to the Orthoplan with its much squarer modern lines.





  Less detailed schematic from Leitz showing a later Ortholux.

Ernst Leitz Wetzlar documentation.


Quality engineering.

Using a 1956 Leitz Ortholux fine engineering can be seen throughout with excellent tolerances on moving parts whilst fit and finish put to shame many a stand of today. Relying on decades of experience prior to the Ortholux, Leitz produced a stand where the quality of all parts speak for themselves, to make a microscope to the same standard today would be costly indeed!

The Ortholux was the earliest microscope to use a totally modular approach in the way numerous accessories could be added to the basic stand like fluorescence, polar, phase, epi-illumination etc. Before this manufacturers would sell the microscope for a narrow spectrum of use limiting its versatility. As we know, all have followed this route and stands of today of research grade are built to take many accessories allowing the end user to build up his or her specific requirements.




  Fine engineering on the Ortholux.

In the above picture it can be seen the attention to detail to all parts of the scope like verniers, slide carrier and finish on the objectives, no cheap punched out or painted on parts of today but crisply engineered machining and all screwed together with impeccably finished screws. The counterbalanced fine focus which acts on sliding ball races is noteworthy, it has a lightly weighted action with great precision at all magnifications (1 division = 0.001mm travel).

Although the coarse focus controls are relatively small and thin compared to say the Zeiss Photomicroscope they work well and have the right gearing for precise control at high magnifications. The fine focus has limited travel indicated by the white lines etched on the body just above the left coarse focus control.




Schematic of coarse and fine focus.

Ernst Leitz Wetzlar documentation.


The stage can be lifted and re-locked on its dovetail mount allowing objectives with short barrels to be used like the Lomo range which is useful on occasion, on many stands this is not possible. You do have to get used to separate fine and coarse focus again after using coaxial controls fitted to modern stands and it is cramped around the coarse and fine controls with the focus lock lever adjacent to the coarse focus.

The nominal tube length is 170mm but unless high NA dry objectives from 160mm stands are used, interchangeability of objectives from other manufacturers is feasible taking into account none parfocality if mixed with the Leitz range.

Leitz DIN objectives with longer 45mm working were introduced later suiting the phase condenser after Zernike, this earlier stand is fitted with 37mm working none DIN Pv phase objectives suited to the Heine condenser and cannot be used in phase with the turret condenser as the phase rings are mis-matched although the bright field position is fine.




Clean uncluttered stage, fitted below is the centrable Berek condenser.

The thick black enamel still has a nice lustre after 54 years, the focus lock lever can be seen in front of the left coarse focus control. The lever on the left near the base front swings in an auxiliary lens for the illumination, this is normally left in the light path. The style of this lever changed on the later Ortholux becoming a thin wedge.

Typical standard equipment from looking at the price listings of the time for my Ortholux were a square stage with drop down X Y controls, four turret nose piece (brochures also show a five as an option) which works well with a positive click for positions and numbering for objectives, at least on the four turret fitted here. It works on the old sliding surfaces technique rather than a ring of many small ball bearings in the turret perimeter often found in todays higher priced stands but works with smooth, precise action and to complete the line up, a centrable Berek condenser seen fitted above.

The Berek condenser is a two diaphragm design the lower ring taking over the role of the field diaphragm situated on the base of most microscopes, the earlier Ortholux did not have a field diaphragm in the base but later ones did allowing use of the more modern Leitz turret phase condenser. The long arm above the ring sets condenser aperture.

The condenser is of excellent optical and mechanical design being well corrected and with the standard screw-in top allows maximum aperture dry 0.95 but with the oil top (often missing today in sales) NA 1.4. If you own the Heine condenser you can use the push on spring filter clip that comes with the Heine allowing a small green or blue filter specially shaped to fit as this is inter changeable with the Heine condenser as they both have the same diameter tube at the bottom. The Berek top element may be swung out of the optical path by a substantial knurled aluminium control for low power objectives increasing its versatility with minimum fuss.




Dry and oil top for the Leitz Berek condenser.



Detail of trinocular head fittings.

The pictures below shows the sprung release leaver for the viewing head, the latter being removed by pulling up on the dovetail slider seen on the right picture. Also seen on the left picture is the slider which permits 100% of the light to be either directed towards the photo tube or the viewing head (this later changed to 80:20% photo/viewing or 100%viewing) this became a push-pull knob situated at the front of the trinocular body. Other viewing heads were the standard binocular head and a monocular with upright camera attachment. Various camera options were available at the time including large format film and a smaller adapter with built in shutter for Leica cameras shown later in the article.

Modern digital SLR bodies can be fitted to the trinocular port as a standard 23mm tube is used and adapters are available today to convert this to T2 mount or with further adapter rings to Canon, Nikon etc bodies. A suitable eyepiece will have to be selected, I believe there were dedicated photo eyepieces but I would think a Periplan would suffice for most purposes but this has not been tested up to writing this article.

It is surprising I think that being of research grade the stand did not have a dedicated slot for an analyzer or filter on the older Ortholux, later ones did, seen as part of the nosepiece, the picture on the right below shows a position recommended in the manual to place an analyzer which was available as a Leitz polar accessory, here fitted with a home made analyzer adapted for the purpose snugly sitting on top of the protruding nose piece optic.





Details of trinocular mount, the right picture with home made analyzer fitted.

The large knurled control shown in the above picture on the right is the release control for the nose piece, care must be taken with this that it is sufficiently tight not to let a fully populated nose piece and objectives slip and strike the stage. This also fits on the lower part of the same dovetail and the nose piece offered up from below until it hits the stop provided with the stage dropped to a low point and condenser removed, this action normally done at the first assembly stage of the stand.


Illumination.



Lamp assembly.

Illumination is in two parts, the bulb housing finished in black 'crinkle' paint is pushed home and clamped into the optics enclosure. Three insulators isolate the heat from the latter to the main body of the microscope whilst some heat is allowed to exit from the top of the ducted black metal enclosure, the optics enclosure is a tight push fit into the rear of the scope with no clamping whilst a filter slot next to the port can accept large glass filters specially made for the purpose. With the lamp enclosure blue filter fitted and 4 amps selected on the power supply bright, even illumination with good white balance can be obtained after adjustments, at the maximum bulb rating no filter should be required for camera attachments.




Glass filters, left for Heine or Berek & right, for lamp.

A 30 watt low voltage filament bulb driven by an external AC power supply is normally used with the Ortholux with the possibility of adding higher wattage specialist bulbs and supplies for more demanding techniques with additional fitments to the basic stand. Directly after the bulb there is a fixed frosted glass lens this prevents true Kohler illumination but is typical of many stands and has become the norm of today. I would have preferred a swing out frosted glass as this is inefficient and reduces light output when you most need it at the limits of highest magnifications and oblique illumination.

A variable collector lens in the lamp enclosure actuated by a long arm is adjusted to provide an even field which can be adjusted while viewing with a 3.5x objective and wide field eyepieces or putting a frosted glass on the base of the scope and viewing the effect of adjustments. The substantial alloy screw clamp holds the bulb housing in position also allowing some further adjustment by loosening and pulling out the lamp slightly for even illumination whilst concentric controls adjust the centering of the filament.

Power supply.




220V/120V ac mains power unit.

Measuring 19 x 12 cm (h w) this unit provides low voltage ac power to the Ortholux, due to the nominal 220V working for Europe, the 240V of British supplies increases the amount of hum from the transformer laminations although the Leitz documentation says it can be used for 220-240v ac. The hum will vary from one sample to the next and is made worse by the metal enclosure but was noisy on this unit. Unlike Wild power supplies with similar construction I have seen which have a dedicated transformer primary tap for 240V as well as 220V this does not.

There is no voltage indication only current, a red line indicates the maximum recommended 6 amps for the lamp whilst a large plug with its own on/off switch brings the mains supply in together with on/off and variable current supplied by the rheostat on the front actuating a sprung metal arm with carbon roller which rotates up and down on the specially cut secondary winding of the transformer, crude but effective if contact surfaces are clean, I have had no problems with flicker and output is steady.


Optics.

A large range of objectives are available for the stand too long to list here from high numerical aperture apochromatics to long working distance and epi-illumination in sophisticated single mirror mounts, both the earlier 37mm and later DIN 45mm working objectives can be accommodated as mentioned, the latter may be a safer bet as less likely to be suffering the delamination problems which also cause grief amongst buyers of Zeiss objectives of the period.

The Leitz pre DIN objectives mentioned in this paragraph worked competently. Fitted to this stand were the 3.5x 0.1 achromat and three Pv phase objectives: 10x 0.25 & 20x 0.45 achromats & 90x 1.15 oil immersion apochromat. Missing was any 40x objective. Although not marked as such the 3.5x and 10x achieve good plan characteristics for their age and give a fair account of themselves on many subjects including larger preparations like plant sections or insect mounts, the 20x I think is rather under whelming both in and out of phase use as the numerical aperture is limited. The 90x apo performs OK within the limitations of its NA and is suitable for dark field with the Heine (with oil top) or the dedicated dark field condenser.


Buyer beware!

The following paragraphs are for background reading, you can skip to the condensers section later if you wish. Hopefully the next few lines should form no part of a successful purchase but included for completeness. All too frequently things don't go to plan buying at a distance, especially microscopes, objectives or accessories! We have all probably had our fair share of supposedly tested items both on eBay or from dealers only to find otherwise...

Out of a rather large but odd assortment of optics and accessories supplied with the scope an older style Periplan eyepiece and a 100x objective with iris were suffering from severe delamination together possibly with the latter of oil contamination behind the front element.. the objective was useless, the former passable at best.

Worse was the trinocular head forming a substantial part of the stand. The scope was bought from a European dealer supplying optics on eBay and was sold as optically and mechanically tested. Seen down the left hand eyepiece tube was a 'near square' this required no testing other than looking down the tube with the naked eye, so much for testing, it doesn't even require the scope to be switched on! Delamination of the splitter prism had caused a progressive shadowing of the field of view worsening at the outer edges, the right tube seemed mostly unaffected. An ultimatum was passed to the seller, either the lot goes back or a substantial amount should be refunded and this was agreed.




View down left eyepiece tube.


Do not try this at home!


Without going into detail the defective splitter prism was separated into its two component parts, the prism splits the light path to the left and right hand tube prisms and consists of two prisms the contact surface being a 50% deposit (or thereabouts) mirror allowing light to pass direct to the left tube prism whilst at the same time reflecting light to the right hand tube and is extremely delicate. After cleaning where some dryback of the cement had caused damage to the surface, the two prisms were offered back together with a very thin layer of immersion oil, the two prisms 'locked' together by tape via the none optical surfaces and offered back to the mount, the latter is a simple copper or similar metal bar with two screws (see picture below). Balsam was considered for the contact surface but considered a one off process and if something went wrong in the alignment of the two prisms the whole tube could be rendered useless so immersion oil was considered the better option although medium term 'dry back' is likely to occur.

Alignment of the combination splitter prism is not to be taken lightly as it is a 3 dimensional puzzle, pressure from the two mounting screws together with the prism slew in the mount in minute amounts affects alignment, we are talking fractions of a mm here. Using a graticule eyepiece and a finely divided micrometer slide alignment was achieved with 1 division lateral error and zero vertically between the two tubes.

Small amounts of error between left and right tubes can cause eye fatigue but I am happy to say I have had no problems. I now see two round evenly illuminated discs with eyepieces removed, the mirror damage is not visible whilst viewing but can be seen looking down the eyepiece tubes with eyepieces removed. The alignment itself is slow as an adjustment is made and the viewing tube offered up accurately to the trinocular port, measurements made and the process continued. A long term project is to seek a UK company that can resilver the prism face with a 50% mirror for a proper repair.





Viewing tube removed from trinocular port. note schematic 'flipped' 180 degrees.

Right image from Ernst Leitz Wetzlar documentation.


Things didn't get much better purchasing a Leitz 40x 0.95 apo objective with correction collar later bought from a well known European dealer to complete the turret as I have no Leitz 40x objective, initial findings suggested it was defective as the correction collar was always right at one end independent of the range of modern and older slides tested and images were ill defined and lack the 'pop' from a good apo. It turns out it had multiple delamination problems within the elements easily seen with a phase telescope and indeed partially by a simple 5x lens with objective held up to a window!

More time wasted chasing refunds and yet another trip to the post office, they know me well down there! The response from the dealer after time wasted checking, packing, paperwork, emails and sending it back was 'better luck next time' ... there will be no next time! This is by no means an isolated occurrence with eBay sellers and dealers across the board over the years.


[Editor's note: Unfortunately Ian Walker's reported poor experiences with some mainland Europe microscope dealers also mirror mine, both buying and building up a Zeiss Photomicroscope III and major unnoticed faults of a Leitz Diaplan purchased.] 




Is this the picture of a new planet, no it's one plane of delamination on the defective 40x 0.95 objective pictured using the Betrand lens of a Zeiss Photomicroscope!


A quote from an American dealer left both me and my brother speechless, asking for a price by email on their advertised Leitz 40x 0.7 Pv phase objective as no prices were given on any items listed, the response was $700 and a further maybe 'up to $100' for shipping! It was obvious they had no interest in international orders.


Condensers.

All the condensers on the Ortholux use (approx) a 46mm sliding mount allowing quick placement, no locking screw is provided you just push home the condenser to its limit in its mount. All are solid and well finished and provided grease hasn't hardened which is possible in the centering mounts and moving parts which may need attention, are a pleasure to use mechanically.


Heine condenser.



Heine condenser with oil top removed, spring filter clip and blue filter.

The above picture shows the Heine condenser together with oil top removed and spring clip which can be fitted to the bottom to allow the purpose made small blue or green filters to be inserted safely. Some sales on eBay that I have seen, the clip, oil top and filters were not sold with the basic unit, I guess many have been separated over the years from the condenser and get lost which is a shame as it increases the versatility of the unit.

Unlike the Berek which I like for general use, so far I have not had great success with this condenser, yes it is versatile allowing circular oblique illumination (COL), variable phase and dark field to be achieved by the rotation of a single control for different objectives but the ring of light I think is too thin no matter the aperture set creating what appears to be diffraction artifacts using COL, a study of the optics I can find no obvious problem but due to this phenomena phase is inefficient due to the narrowness of the illumination ring and COL has gone past what I think is its optimum setting.

I do not agree with Leitz in their documentation that the condenser operates smoothly at all settings between bright field and dark field as the illumination always remains one of circular oblique whether of larger (filling the back focal plane of the objective) or smaller diameter (say within the phase ring of a Pv objective). Yes, there is a bright field 'effect' but not the same as say a standard brightfield condenser like the Berek and again the image to me looks one of a condenser too stopped down at the majority of settings.



Heine condenser illuminating ring 20x Pv phase objective in use, due to camera flare this is in reality a little narrower than shown here.

The illuminating ring is approximately approximately 1/2 of the phase ring width on the objective.

I have done hundreds of tests with COL using numerous stands and objectives from 1850's Victorian to modern together with tests using the phase and dark field positions on condensers like the achromatic-aplanatic NA 1.4 from Zeiss and indeed many home made stops fitted to filter trays. Experimenting with these I have always found an optimum width for  the illuminating ring, too thin and excessive reduction of illumination occurs together with artifacts introduced and this sample of the condenser verges on that, so I remain unconvinced of the results but I will persevere with it and possibly find combinations of objectives and settings where it performs better.


Dry achromatic NA 0.9 turret phase condenser.



The condenser could take many years of use!

Ideally suited to the later version of the Ortholux with built in field iris on the base this can still be used on the older stand. Focusing the condenser can be achieved by placing a thin opaque object on top of the glass plate on the microscope base and bringing into focus. A swing out top allows low power objectives to be used. Mechanically the condenser works with great precision, oblique illumination, bright field (H), dark field can be achieved with the older Pv phase objectives but the annuli do not match so cannot be used for phase...

This can be rectified by using the later 'Phaco' objectives but I have not purchased them, interesting though the annuli match my brother's Zeiss Neofluar phase objectives from the Photomicroscope III as tested on ph2 position, 16x 0.4, 25x 0.6 & 40x 0.75 work well, I suspect that the ph3 position would work too for the higher power Zeiss's but this was not tested.

Dark field oil condenser.



Leitz dark field oil condenser NA 1.2-1.4.

Easy to use and unassuming this is a favourite with me for COL on diatoms, ideally suited to modern preparations as slide thickness will affect results. Using a drop of water the drop sitting nicely in the small concave dip of the glass condenser top as it is offered up to the underside of the slide and using a high performance objective like a Zeiss plan-apo 100x NA 1.30 (DIN 160mm) oil immersion superb results in COL can be achieved. The overall characteristics of the COL illuminating ring was determined by choice of objective and condenser immersion medium used, but in this case was brilliant in its nature benefiting from the well computed optics of the Zeiss and the visual image of subjects portrayed with noticeable absence of flare or artifacts.

Recently I acquired a Klaus Kemp strew slide of Amphipleura pellucida in a high refractive mount RI 1.9, thin cover slip and with 10x eyepieces (note the viewing head has a 1.25x magnification factor) the striae were portrayed with great contrast and definition whilst punctae within limitations of eyepieces and my eyes, well defined.

The centering when first used was found to be seized due to hardened grease in the mount but after refurbishment works well and once set needs little adjustment on further insertions into the microscope stand. I would have liked to test the condenser with a Leitz fluorite NA 1.30 objective of the period but unable to source at the current time.



Compact Leica camera attachment.




'MIKAS' micro attachment for the Leica film camera body.

This came with the microscope and occasionally they can be found at dealers or on eBay. The eyepiece is slotted in the alloy ring at the base of the adapter after unscrewing from the main body, only certain eyepieces can be used the older Periplan's are OK, the newer ones won't fit. A focusing telescope is used which has graticules marked. The unit is offered up to the 23mm camera port on the Ortholux and clamped in position. Different adapters can be screwed onto the 39mm thread originally designed for Leica camera bodies, here shown with an adapter for a Sony NEX mount digital camera.

A cable release allows speeds from 'T' & 'B' setting up to 1/125th of a second, later 'MIKAS' attachments may differ in style and the highest shutter speed used. The complex 'Compur' shutter mechanism also found on press cameras and many others of the time is notorious now for not working on one setting or another, this one is fine on all settings except 'T'.

The correct cable release with long pin protrusion is required to operate the mechanism successfully, the one which came with the adapter was defective, shown above is a short lead one from years ago hiding away in an old accessories box!

As yet I have not attempted any digital camera work with the microscope, this article may be followed up with another covering this in more detail.


Conclusion.

The Leitz Ortholux is a fine microscope built to standards not seen in the modern age, it would be too expensive to produce and last far too long so wouldn't be cost effective.

A good range of accessories were available originally although getting harder to source now including a sizable selection of objectives. The pitfalls (and this is most noteworthy) must always be one of finding a good sample that has not been abused and relying on the experience, quality of checks and honesty from the seller whether eBay or dealer in regards all is well with both stand, accessories and objectives.

It is becoming much harder to source 50 year old optics whether Leitz, Zeiss or others that are in first class condition, free of defects and no matter what the fineries of any microscope it is only as good as the objectives, eyepieces and condensers fitted, this is why many prefer to use more modern designs.


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