A tour around the Zeiss Photomicroscope III

With some notes on the Photomicroscope range and the pros and cons of a large research stand cf. a student stand like the LOMO Biolam. 

 A hobbyist's perspective by David Walker, UK.

The author has been using the popular LOMO Biolam microscope as a hobbyist for almost thirty years but a few years ago had an opportunity to acquire a Zeiss Photomicroscope III ('PM III') in a basic transmitted light configuration. The variants of the three Photomicroscope models crop up for sale quite regularly, so presented below is a tour of the PM III with a few thoughts on owning this model from a hobbyist's perspective and its use compared with a typical smaller stand. There probably couldn't be a much greater difference in the 'microscope model spectrum' between the PM III and Biolam, and the author has found it very instructive learning the pros and cons of both.

Paul James wrote an excellent illustrated article on his Photomicroscope I in the July 2001 Micscape, including an internal view of the complex optical array and the 35 mm film arrangement. Many design features of the photomicroscope i.e. substage, stage, focussing, Optovar mag changer are essentially the same or similar across the models I - III and many are discussed in Paul's article; the models differ mainly on how the camera and lamp control are implemented.

The Zeiss Universal and Photomicroscopes have a very distinctive size and shape and unlikely to be confused with any other model in the Zeiss range. Within the range though, examples are sometimes misidentified in online auctions. The table below is an attempt to summarise some key differences between the three models; the Universal is included for completeness. As others have commented, the most instantly recognisable feature to split the photomicroscopes is the number of meters on base: no meter - PMI, one meter - PMII, two meters (and distinctive film speed dial at front) - PMIII. No meters and no internal 35 mm camera canister visible on right of limb - Universal.

Sources for Table data: Downloadable public domain manuals for Universal, PM I, II and III; in addition for PM III - own example; for PM I - Paul James' article and personal comms.
*Updated Dec. 28th 2007. Thank you to Spike Walker who tells me there were four models of Universals.

History: The author hasn't found any info' on the timeline of the Photomicroscope range (and would appreciate any info' on dates), but if the two figure number on the back of the manuals is the publication date, these may provide some guide as to a typical production year for each model: PM I - 1963 and 1964 manuals, PM II - 1970 manual, PM III - 1975 Zeiss advert of their microscope range in 'Guide to scientific instruments'.

Zeiss PM III (above): Although a bulky microscope the curved sweep of the limb makes it less dominant on a table. The wide flat base is quite handy for keeping slides being studied off the bench. Size (includes lamp, film speed extensions except accessory top tube): 24 x 11 x 17 inches (dxwxh).

This side of the limb has the plug-in filters (green, 4 neutral density, blue), the lamp control and the film canister. By using combinations of the neutral density filters, light transmittance from 1.5% to 100% light can be selected in increments of a factor of two. A frame counter, and memo for type of film used is on this style of film canister. A push-in pin lower left of film canister allows multi-exposures on one frame.

This example has the 12V, 60W tungsten lamp which the author has found more than adequate for most work. The lamp has a swing in diffuser in addition to diffuser under microscope base (see below). A 12V, 100W halogen lamphouse is a common alternative. The focussing stage and substage is by visual inspection of manuals a similar (same?) design as used on Universal / earlier Photomicroscopes and the Zeiss WL. A phase condenser is shown.

The head includes an Optovar mag changer/Bertrand lens, and push-pull beam splitter for directing light to binocular-built-in camera-accessory top port. (See Paul James' article.)

The features this side (from manual) are:
A - spot or integrated exposure selection,
B - cable release, all light goes to film if used,
C - changes duration of flash appropriate to film,
D - flash ready illuminated button,
E - for lead to flash generator,
F - transmitted or incident light selection, latter requires appropriate epi- accessories,
G - socket for remote control either by a 'pedal switch' or 'pulse generator'.
The 'computer flash' module is shown in the manual but don't recall seeing one advertised. A simple beam splitter on the field diaphragm can serve well for dual tungsten / flash work (a simple design suitable for the PM III is described here).

The PM III has a distinctive film speed control dial (above left), a secondary dial allows smaller ASA / DIN increments. This is quite vulnerable to knocks in transit so worth checking OK if an example purchased. The four camera control buttons, left to right are standard camera 'B' and 'T' shutter control, 'i' multi-function and 'A' exposure button.

Voltmeter and exposure indicator meter on left and right of base; the latter (uncalibrated) provides info' on progress of exposure and likely shutter speed range for the current light level. Shown left above after repainting as the paint had badly flaked off this example's meter (right above), but my brother Ian stripped the meter and painted / re-inked scale in similar style (using a photo of meter kindly provided by Steve Durr, a fellow PM III owner).

Footprint - don't forget the power supply: Like many research scopes, the photomicroscope has a considerable 'footprint' and weight so a potential purchaser needs to ensure there is a suitable table and working area, particularly in a domestic environment. The power supply of the II and III models are very large but they have key differences that can impact on the overall footprint as shown below. Reducing the footprint from model II to III was apparently a design consideration as a 1975 Zeiss advert for the PM III notes  '... and now even more compact with all the electronics and controls built into the base'.

The PM III power supply (above) has no voltage / camera controls (unlike the PM I and II) and the rubber feet permits it to sit vertically under a desk at the back. Two multi-pin cables and the lamp power supply go to the scope. There are voltage outlets for 6V, 12V. The power supply is very solidly built (Size ca. 6 x 9 x 16 inches hxwxd).

Above: Zeiss Photomicroscope II and power supply for comparison with I and III. The features on the microscope limb differed between the three models, especially between I and II / III. See manuals for details. To save desk space if the camera wasn't used, presumably the power supply could be run at full or desired voltage, put out of the way and the microscope neutral density filters used to control the lighting. Right: A 'sturdy work table' was available from Zeiss for the II to avoid using desk space for the camera control / power supply. It must have been a sizeable table, it makes the PM II look small! Note added Nov. 13th: Thank you to Mike Samworth who explains that 'originally the desk was designed for the (much) bigger Ultraphot model'. Image source: Zeiss Photomicroscope II manual (1970?).

Right: Zeiss Photomicroscope I and power supply for comparison with II and III. The external power supply / camera control was relatively compact for the PM I as was designed for the 6V / 15W lamp. Higher intensity lamps were available but would need their own power supply. The PM I has quite different control features on this side of the limb compared with models II and III. These are: a silica gel canister to keep the photometer dry; additional two setting mag changer for image size on the film plane; shutter speed dial. Image source: Zeiss Photomicroscope I manual (1963?).

If a potential user was anticipating adding certain additional lighting options to a photomicroscope, the considerable increase in depth and/or width of the unit needs consideration! The author's domestic desk only just fits the PM III with 12V 60W lamphouse depthwise.
Left above: the 'special purpose illuminator' shown on a PM II. A high intensity multi-purpose lamphouse and 12V / 60W lamp are switchable, ('bolt-on' item not needed for just the latter lamp alone).
Right above: epi-fluorescence unit shown on the PM III, this gets my vote for the ugliest implementation of additional lighting!
Image source: Zeiss Photomicroscope II manual and Epi-fluorescence III RS manual.

Photomicroscope III base: 'No user serviceable parts inside' as the saying goes, but heh, microscopists are curious! The bottom plate readily unscrews. The push-in filter assembly is clearly seen. The lamp intensity control electronics are top right.
The front camera controls are relay activated* and the cylindrical soldering loom inside the ASA speed selector housing is a marvel (not seen above). Hopefully the long term reliability of this complexity is good! (*Thank you to Martin Canny who tells me his later model of a PM III does not use relays.)
'D' marks the Allen nut to swing in the additional diffuser (a hole in bottom plate allows access but not always easy to mate the Allen key), shown on removed optical tube on the right.  

Miscellaneous notes
Objectives: The distance 'd' from objective barrel to focussed subject is 45 mm for Zeiss objectives 'since 1950' (Ref. Zeiss 'Optical Systems for the Microscope' p. 12). The focus range of the Photomicroscope doesn't readily take short barrel pre-DIN optics e.g. the LOMO range (d = 33mm) with stage in its usual position unless an objective extension collar is used. At least two designs of extension collar are available, a variable and fixed length design. I bought a well made variable extension brass extension collar to do this from eBay but didn't find it very secure. A fixed 12 mm extension collar custom made by another eBay seller was much better. The tube length increase may introduce aberrations for sensitive objectives. 

Condensers:

On the PM III condenser mount (above left), the locating pin (P) to prevent phase/DIC condensers rotating in the mount is at the rear which mates with a notch on the condenser dovetail. If sourcing condensers independently of the stand as the author has, the notch and pin position may not match, presumably depending on the condenser's vintage and/or stand it was sourced from. (A PM I and PM II manual possessed, shows the centring screws at the back and locating pin at front, i.e. the reverse of the PM III).
If the author's experience with phase condenser above right is typical, the notch doesn't have to match the pin as it moves fully back in its mount on the PM III. The phase ring is free running so doesn't twist the condenser. To be sure, I've added small discs of very thin foam (light baffle for camera, the dark grey discs in image above right) just to add a bit of friction. May 2008 addition - I've now taken these off as raises condenser slightly and potentially allows the condenser to be focussed into slide.(Some dovetail designs may be rotatable after removal to correct this although the author's two aren't; others had dovetails with notches front and back so wouldn't be a problem. The Abbe condenser that came with this stand has a notchless dovetail.)

Polar work: the turret head has an inset for a Polaroid analyser and a second slot for a retarder at 45º, a polariser can sit on the field lens or filter tray. So even without Zeiss polar kit, homebrew qualitative polar is straightforward, coupled with the rotating stage which the Photomicroscope is often supplied with.

Delamination: The microscope frame optics on the author's example are in excellent condition but some of the supplied objectives weren't (unless a seller, private or dealer, is very thorough, delamination can be overlooked). Spike Walker has an excellent overview of this problem of Zeiss optics of this era on his Ultraphot Shop site (as well as a discussion of the DIC options for Zeiss microscopes). The present author's comparison of a delaminated and a perfect lens of same design is in this article; some of the image quality may be brought back in software for damaged objectives.

Purchasing notes: Cost isn't necessarily a deterrent to owning a Photomicroscope cf the smaller Zeiss stands. Because of their bulk and limited appeal, ('boat anchor' I believe is used in the radio ham fraternity for equivalent kit), Photomicroscopes and Universals can sell in a comparable price range to smaller stands, in Europe at least.
A Photomicroscope III in good condition sold for ca. £400 in UK last year on eBay without objectives. Stripped stands can be £50+ and useful sources eg for spare focus blocks and base components. Suitable lamps, substage kit and optics come up frequently as many components are shared across the Standard / WL range of the same era. The achros and planachros of this era sell for quite modest prices as widely available. 
The Photomicroscope III is a complex stand mechanically, optically and electronically so a private purchase can be a gamble. The author's example was dealer / service agent sourced with a 6 month guarantee, so if the photo side is important it may be worth the extra a dealer will charge.
For safety, especially if a private purchase, it may be advisable for the external power supply and internal electronics to be checked by a qualified person (my brother Ian, an electronics engineer checked out this example).
Shipping: Ideally personal collection is advisable if possible, as research stands can be a victim of their own weight if courier shipped and requires careful packing to ensure no damage. All modular parts can be removed and packed separately; stage, substage, condenser, beam splitter head, binocular head, optics, lamp and the power supply packed in a separate box.

Why own a large research microscope?
I suspect that I'm not the only hobbyist where ownership of an older large research stand (whether it be a Zeiss, Leitz or other maker) isn't entirely based on rational arguments! Perhaps an overused but valid analogy is enjoying the traditional engineering, driving feel and lines of a classic old car despite its foibles and certain impracticalities.
If space, portability and design simplicity are important criteria for choosing a stand, the Photomicroscope wouldn't be high on the list! Smaller stands like the Zeiss WL and the various Standards of the same era can perform most of the transmitted / incident light techniques with appropriate accessories including DIC and fluorescence.
The long term reliability of the electronics and photometer in the PM III is uncertain, although the author only uses the 35 mm option occasionally. If the internal camera or complex limb optics of a Photomicroscope I, II or III fails you still have what effectively is a Universal stand! (From inspection of Zeiss' cutaway drawings I believe the image path is only sent 'round the houses' in the limb for the internal photo mode; the top accessory port and bino' optics are limited to the beam splitter head).

Little 'n large: Photomicroscope v. LOMO Biolam
When I first started using a Photomicroscope, I thought the Biolam outfit would be sidelined; how wrong I was. The Biolam sits proudly next to the Photomicroscope and use both regularly. In case of interest, below are my own preferences for each stand:

LOMO:
- Studies at high mag / resolution eg. diatom studies. Although the mechanical stage and overall stand stability is far better on the Zeiss, I like the optical simplicity of a LOMO stand i.e. subject -> objective -> eyepiece -> camera cf. the complexity of the Zeiss (Telan lens in nosepiece, Optovar, beam splitter...). LOMO's better objectives with their Zeiss Jena design pedigree, give Zeiss (West) optics a good run for their money in the resolution stakes if not flatness of field.
- I prefer the LOMO fine focus at the highest mags, it is a lightly loaded mechanism with little vibration transfer from fine focus to stage. If using small sensor digital cameras on a microscope e.g. for diatom studies, the sensor 'crop' effectively increases the final mag (not 'empty mag') when the image is viewed on the computer screen and is a critical test of any focus / rigidity issues—albeit possibly beyond the visual and 35 mm imaging requirements a stand was designed for. But the LOMO Biolam and some other stands I've used under the same conditions seem to have a better overall image stability in this respect at the highest mags. From one example of the PM III it is hard to decide if attributable to one or more factors like wear with age, need for servicing tweak or stand design but may be a typical example of a PM III stand bought in this era.
The focus on my own example of the PMIII is the most frustrating design aspect. The focus supports a heavy stage and condenser with their mounts. If the coarse focus tension isn't set quite high, the stage will creep. I'd be interested in hearing from fellow Photomicroscope / Universal / WL owners as to whether this creep is typical.
Update: July 2011: Thank you to a Photomic owner who has had his serviced by Zeiss, who tells me if working correctly and properly serviced the focus should not creep when tension is set low. This suggests my example is worn or needs servicing.
- Home brew mods: the external mirror design makes dual flash / tungsten easy to setup and also multispectral studies (near IR, near UV, monochromatic deep blue) by changing the lamp bulb for suitable LEDs.
- Objective flexibility i.e. pre-DIN or DIN of any vintage for 160 mm tube (parfocality issues aside).

Photomicroscope III:
- Low to medium mag studies because of the evenness of built-in lighting cf. the quite poor evenness of light offered by the external LOMO lamps for the Biolam.
- 35 mm photography: not surprisingly this stand excels at it, parfocal, built-in camera, auto-exposure, one button push exposure.
- multi-technique transmitted light studies without condenser changeout, the phase condenser allows phase, some darkfield (or DIC if you can afford it), COL, brightfield, oblique and homebrew polar is easy to add.
- Digital SLR work, the spare top port and large mass of the stand makes for a good stable stand for direct coupling of a DSLR (in the author's domestic environment a huge external support for the camera is not practical.)

The author's current setup in a spare bedroom. The LOMO Biolam gets just as much use as the Photomicroscope. A computer is out of shot on the right for direct imaging to a PC for either microscope. The footprint of a small student stand like the Biolam with external lamp, PSU and table to bring its height up can be comparable to that of a large research stand!

I enjoy using the LOMO in parallel with the Zeiss because it is rewarding getting the most out of simple kit and working around a student stand's limitations. In comparison, the Photomicroscope was designed for 'turn the handle' reliable microscopy as a research stand. It's hard to quantify the pleasure of using and being a custodian of an old classic research microscope whether it be in this case the Photomicroscope or other classics from makers like Leitz.

Comments to the author David Walker are welcomed.

Acknowledgements and Sources: To compile the comparative data on the models above and for greyscale images, the author was heavily reliant on manuals for the Photomicroscopes I and II (any errors in interpretation and compiling above notes appreciated) and for Paul James for sharing his experiences with the Photomicroscope I and for his Micscape article on this model.
The older model manuals are available online (see below) and the author thanks contributors to the science-info.net site and for Yahoo Microscope forum members for scanning / donating copies and for Gordon Couger for hosting them.
Thanks also to Ron Neumeyer for access to an early copy of the Photomicroscope I manual which contained additional info' to a later copy.
Thanks also to Mike Samworth for valuable comments post publication and to Spike Walker for valuable info on the Universal and Photomicroscope models, post publication.

Selection of online resources relevant to the Photomicroscope:
Carl Zeiss Photomicroscope I by Paul James, Micscape 2001.  An excellent illustrated tour and review of the model I and the author's experiences on using it. Includes image of internal limb and use of the camera. A number of features are common / similar to the III.

Zeiss website Zeiss generously make microscope and related accessory manuals freely available for many of their current and older models available on their website (follow 'Microscopes', 'Support', 'Instruction Manuals' links.) For the Photomicroscope III these include manuals for transmitted light, incident light, epi-fluorescence unit, 60W lamp, 100W lamp.

science-info.net This site hosted and administered by Gordon Couger has a continually growing collection of non-copyrighted manuals for older microscopes kindly submitted by enthusiasts. Zeiss manuals include the Universal and older Photomicroscopes. Of particular note and a recent generous addition (Nov. 2007) is the rare 'Optical Systems for the Microscope' - Zeiss' 97 page in-depth review of all aspects of optics for their microscopes in the Standard / Universal / Photomicroscope fixed tube length era.

Microscope forum Ron Neumeyer kindly offers an early copy of the Zeiss Photomicroscope I manual on his valuable microscopy resource site which complements the later one on above site.

Steven Durr's home page Steven shares his wide variety of interests including 'My microscopes' link where he discusses the microscopes owned including a Photomicroscope III. Also superb galleries of photomicrographs.

'Droplet - amateur microscopy of the protozoa' Piotr Rotkiewicz's website includes excellent annotated images of protozoa and also a page on his microscopes which includes a Zeiss Photomicroscope III which he describes as his 'workhorse'.

Dr David Webb's homepage Includes illustrated step by step tutorials on the use of the Zeiss Photomicroscope II, which forms part of the courses run at the Universty of Hawaii at Manoa. (Thank you to Dr. Webb for permission to link to these university course pages.)

Micropolitan Museum of Microscopic Art forms Wim van Egmond's renowned imaging includes those taken on a Zeiss Standard and a Zeiss Photomicroscope.

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