3D Image Enhancement made EASY – Part I [Updated April 27]

Click on image above for larger version.

Recent posts covering the Goerz '3D' Condenser have sparked interest in creating an alternative approach suitable for use with ordinary (Abbe-type) condensers.

The goals of this new effort were: (1) Low cost and Ease of construction, (2) Improvement in image contrast and apparent object depth, and (3) Ease of construction and use..

It is important to remember that the goals here are not maximum image contrast nor maximum resolution, but rather to simply achieve meaningful improvements in both (relative to normal Brightfield imaging) by use of the simplest and most generally applicable method possible. 

The method presented here appears to satisfy these goals and results in a simple addition which may be easily applied to an ordinary microscope condenser and, unlike other methods, (e.g: oblique illumination or phase contrast) may be used without any additional/special optics or concern for adjustments during use.

Also, since the light loss is minimal, the device is suitable for use on instruments having limited illumination and/or at higher magnifications than these common alternatives.

The device is constructed as a simple disk having an array of three diffusion segments, which modify the illumination in a predetermined manner and is essentially the same for all objectives, from 10x to 40x, or more. The "radial" approach both eliminates the need for adjustments when changing objectives and also allows the Condenser Iris to remain fully usable as an additional means of image control.

The construction of this Condenser "Radial Diffusion mask" is depicted in the following diagrams:

Note: Click on any above image for a larger view. 

Installation of the mask, its preferred use and example specimen photos will be presented ASAP… 

* * * * *  
Basic Construction Notes:  

Most of the construction details for this mask are non-critical. If the tape intersection point is reasonably close to the optical center of the Condenser when installed, then the device should function as intended. The precise angles are also not critical – anything approaching 90-degrees should work just fine. 

The specific type of "matte tape" to be used is also not critical. Ordinary, generic "dollar store" types seem to work about as well as anything else. As long as the tape width is about 3/4" then disks up to about 37.5mm diameter would seem feasible. Scotch (brand) Matte finish tape, however, apears to be superior to their "Satin finish" variety, which seems to exhibit less desirable diffusion characteristics, at least for this use. 

The acetate disk material is also non-critical. The basic requirements are that it be basically clear, self-supporting and thin enough to be trimmed with scissors. However, if your Condenser accepts a clear Daylight filter, then this might  serve as an alternative substrate. 

The positioning of the Opaque segment was chosen so as to not create uneven illumination with objectives of less than about 40x. However, it may be positioned closer to the disk center if contrast enhancement is desired for objectives in the 16x to 25x range also. In this case, about a third, instead of halfway, from the center to the disk edge may be tried. However, if detailed examinations with 40x and greater objectives are not the primary use, then the Opaque segment may simply be omitted with minimal loss in overall performance. (It can always be added later, if desired.) 

The Opaque segment may be created with a single strip of black PVC tape (plastic electrical tape), located on the reverse side of the disk, so it does not interfere with the matte segments. This allows the opaque segment to be re-positioned, if desired, without interfering with the other segments. 


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An External Mask: 

One common problem with many modern microscopes is that they often use Condensers which lack any sort of proper filter holder. Naturally, this sort of shortcoming might seem to be an issue when attempting to implement even something as simple as a Radial '3D' Mask… 

Fortunately, the design of this Mask is remarkably forgiving when to comes to placement in the Condenser, even to the extent that it can be perfectly acceptable to place the mask outside the Condenser! This can be especially true for use with objectives of >10x, where the loss in Mask performance is basically trivial. (For objectives of ~10x, the loss is most typically limited to a slightly uneven background light level.) 

For Condensers which have a significant bottom flange (e.g: most base-mount types), external mounting of the mask should be possible, as long as the width of the flange's bottom surface is sufficient to allow retention of the tape strips. 

The tape strips are simply applied across the width of the flange, such that the "inside corner" formed where the strips overlap is located approximately in the center of the objective aperture, as viewed from the eyepiece position. (For the most accurate alignment, with the least difficulty, use of the 10x objective is suggested for this process.)  The two diagrams below depict both proper tape placement and proper overall mask alignment (centering).  

(Note: Click on either image above for a larger view.)

Be aware that the tape placement should be performed only after the Condenser has been properly centered in its mount, as for Brightfield use. Once the Condenser itself is centered, any centering mechanism present should not be used to correct any misalignment of the tape strips. If the overall positioning is unacceptable, then the strips should simply be removed and re-positioned properly. Just remember that exact alignment is not essential for successful use!  

The photo below shows typical results when using the External '3D' Mask method:
(Image cropped and downsized from 16Mpix JPEG original. No sharpening used.) 

(Note: Click on above image for a larger view.) 

Additional photos using the Radial '3D Mask' will appear in the next post – so, stay tuned…


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The Goerz 3D Condenser – many Surprises?

The primary mystery surrounding the Goerz 3D condenser is, "What is this thing supposed to do, and, how is it supposed to do it?"

Fortunately, careful testing of this 'Mysterious' condenser has led to a better understanding of its intended workings. However, not only that but this testing has also uncovered a number of surprises surrounding its design and use.

All of this hinges on understanding the functions of strange plate located in built into the bottom of the condenser, a few mm above the Condenser Iris. This plate has a clear central strip (or, 'slit') about 3.5mm wide separating two partially-silvered areas, which exhibit about 25% light transmission, and together fill the remaining aperture area.

The key to understanding this Condenser seemingly lies in understanding the intended function of this central slit.

To better appreciate this, consider a normal condenser where the Iris is closed down such that the objective aperture (as seen in the rear of the objective) is only about 1/4 to 1/3 open.

Under these conditions the effective NA of the objective is reduced considerably (to just a bit more than 1/2 of its rated value, actually), the image contrast is increased, and also the 'depth-of-focus' in the Object plane is increased somewhat. However, all this is accomplished at the cost of object resolution, which is reduced to about 1/2 of its maximum value. Even worse, this form of masking results in an image that is objectionably harsh and prone to various undesirable artifacts.

Now, consider what happens if the normal, circular Iris opening is replaced with a slit opening of the same width, but whose length spans the full aperture of the Condenser…

In this case we might expect full resolution in the direction of the length of the slit but also an increased depth-of-focus in the direction of the width of the slit. In this way we might hope to achieve improved image contrast and 'depth-of-focus' while sustaining only minimal loss of resolution. However, although image brightness is somewhat better than with the minimally-open  iris method (above) the image is still a bit darker than normally desired and some image artifacts may still be observed.

Now, making the "sides" of this slit semi-transparent, instead of fully opaque, would seem to offer the prospect of moderating the least-desired effects – increasing image brightness and minimizing possible image artifacts, while also allowing the device to be used "normally", if desired, with little loss of imaging performance. This seems to be the Goerz approach, based on examination of the device and initial testing.

So, this is the current thinking on how the Goerz might have been intended to work – no magic, no Mystery; just some basic physical optics!

In other words, the "3D" effect seems to be mostly marketing hype for a slight, directionally-biased increase in 'depth-of-focus' resulting from the use of a somewhat unique, built-in slit aperture.

Since it was not practical to remove the critical 'slit plate' from the Goerz condenser, testing of this concept was performed on a similar (but totally normal) common NA 1.25 Abbe-type condenser.

Different Slit-type masks were compared with normal Bright field and with common COL-type masks in a preliminary effort to determine whether Slit-type masking provides any observable benefits, and, indeed, any detectable "3D" effect.

The initial results of these tests are summarized in the photos below…

(Click anywhere on the above image panel for a larger version.)

The there are two big surprises revealed in these photos: (1) despite its novel design and construction the Goerz design actually performs rather poorly as a "3D" device, barely equaling the depth-of-focus performance of a number of more common alternatives (as shown), and, (2) the real surprise lies in the number of alternative methods which easily equal, if not surpass, the performance of the Goerz device, both in terms of resolution and image contrast!

In other words, despite its novel design, elaborate construction, assortment of optics (optional tops) and unique optics-offset adjustment, the device seems to do nothing which cannot be accomplished by simple alternatives.

It only genuine attractions are its low-power (NA ~0.5) Brightfield mode (using no top), and its Darkfield modes, all of which are mildly compromised by the presence of the non-removable "3D" slit gizmo embedded in the basic design.

As far as possible "alternatives" are concerned, it may be noted in the photos that these all seem to offer results which are basically similar, differing mainly in the presentation of image details, as well as ease-of-implementation and ease-of use. All of this, of course, being potential food for a future post or two…

See the post of March 28, 2017 (below) for more on the Goerz '3D' Condenser. 

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The mysterious Goerz '3D' Condenser! [Updated 30 Mar 17]

A little-known child of the "Flower Power" era, this unique device was served-up with a thick layer of marketing hype, such as "plastic field," and similar nonsense. 

Sold by the C. P. Goerz American Optical Company, the device had nothing to do with the "real" American Optical Co., and the cryptic labeling was a cause for much confusion (and perhaps even some litigation). 

Still, it seemed to offer at least some promise as a potential, low-cost alternative to more the established methods, like Phase Contrast and DIC. 

But, what Secrets does it really hold? And, will it really measure up to all the wild claims made for it? 

Stay tuned to this Blog to find out!  

 * * * * *  

[ UPDATE ] 

The sample unit (shown above) was contained in a fitted wooden box, together with an aperture viewing telescope, a set of three slip-on tops and an adapter ring for the mounting sleeve. An iris diaphragm and swing-out filter holder were attached to the base of the main unit with three small screws, which would allow the iris unit to be rotated, if needed, and then locked into position. 

   

The basic condenser was provided in a European-standard 37.0mm sleeve mounting. Unfortunately, instruments using this size mount are not common in the US and this diameter is a bit to large to fit the JIS-size sleeve mount (36.75mm) which is far more common (e.g: Nikon-S, Olympus BH and CH, etc).  

   

However, included in the set was an expansion sleeve (adapter) which enlarges the Condenser mount size to 39.5mm (the old Leitz/Wild size). Reportedly, there is also an adapter sleeve for 38.75mm mountings (RMS, B&L) but this was not present with the sample tested. 

     

The condenser unit itself appeared to be a conventional 3-lens design, with the third lens provided as a slip-on option. A brightfield top of NA 1.2 ("A 1,2") and a pair of darkfield tops ("A 0,65" and "A 0,8-1-1,2" – as shown above) were included. (The later top presumably provided NA 0.8-1.0 "dry", and 0.8-1.2 when used with oil.) Oddly, there were only two positions in the fitted case for such tops, although a total of three were actually provided. (There were also three slots for filters, but none were included with the sample unit. These were reportedly Blue, Green and Ground glass types.)  

   

By itself (with no top) the condenser appeared to have a NA of approximately 0.45, or so, since it filled the rear aperture of a 20x/0.40 objective but only about 2/3 to 3/4 of the aperture of a 40x/0.65 objective. When the A1,2 top was added, the rear aperture of the 40x/0.65 objective was easily filled, with the condenser iris a bit more than 1/2 open. (Details of the internal optics of the device will be presented in the next update.) 

Still, the main question to be answered remains, "What, if anything, does this thing actually do?" 

And that can only be answered by actual testing…  

* * * * * 

Variable-color Phase Contrast ?

AO seems to have dropped the ball with their Polanret Variable Phase Contrast system – too complicated, too expensive, and (for many users) just too hard to understand! Yet AO was not the first maker to venture into the 'variable-phase' waters…

Way back in the late 1960's Nippon Kogaku (Nikon) introduced a "polanret" type system of their own, intended for use on their Model "S" series of stands. However, unlike the later AO system the Nikon system was simple, compact and rather affordable. It also distinguished itself by creating user-controllable interference colors in the phase images!

And, apparently just to ensure that potential users had no idea what it was, they called their marvelous new creation, Nikon "Interference Phase Contrast" (or, more simply, "IPC"). Not even a hint of "Color" anywhere in the official name…!

Now, like the AO system, the Nikon IPC system did not require special objectives but relied on the standard Nikon Achromat types of the day. And, this was probably its Achilles Heel – the excellent Nikon Plan, Fluorite and Apo objectives were simply not supported!

Thus, Nikon offered an expensive accessory that could not be used with Nikon's own highest-quality optics, only with their  lower-end "classroom" type Achromats. What were they thinking…?

But inability to use quality optics was not the only flaw. Since most of their S-series scope had somewhat limited illumination capabilities (the S-Kt and S-Ke models were exceptions), the system relied upon extra-wide openings in its condenser in order to compensate for the light loss within the system. This was coupled with the use of rather generous phase-ring widths in the optical head, a step quite likely taken to simplify system adjustment by allowing a little more "slop" in the optical alignment.

While these measures did allow the system to be used on the lower-cost models, and by relatively unskilled users, it also placed some limitation on the ultimate quality of the resulting phase images.

That said, this is not meant to imply that the Nikon system provides unsatisfactory images – far from it! (See inset detail in the sample image below – click on image for larger versions:)

In fact, with very little effort it is possible to create a wide range of very colorful and highly-detailed phase contrast images using the system. (See end of this post for additional sample images.) In fact, it may be more correct to classify the Nikon IPC system as "artistic," rather than as a primarily "scientific" device.

Now, compared to the rather monsterous AO Polanret system (which weighed in at nearly 15 lbs!) the compact Nikon Interference Phase Contrast system is a marvel of Japanese optical and mechanical technology and innovation. The basic unit, responsible for the phase contrast and interference color functions is less than 10 inches long and sits comfortably (and horizontally) atop nearly any Nikon S-series biological microscope. The matching Interference Contrast condenser is simply a basic Nikon S-series phase contrast condenser with special, extra-wide ring openings, matching those in the optical head.

Control is much simpler than on the AO Polanret unit with a simple horizontal slider-bar holding a set of phase rings and a pair of control knobs to set the optical parameters. Using these the user can set the equivalent of either Bright or Dark contrast, as well as a wide range of contrast amplitudes. (Essentially, one knob selects the background color while the other chooses the level of contrast, although there can be some limited interaction between them at extreme settings.)

One additional, but very important distinction between the AO and Nikon systems is, as one might well expect, that while the AO system is intended for "infinity" type objectives, the Nikon system (naturally) is intended for use with "finite" (or, "160mm") objectives.

Perhaps because of this the Nikon system seems far more amenable to adaptation for use with more modern optics than the simple 1960s-era Achromats for which it was designed. In fact, with little effort the Nikon IPC system functions very well with some of Nikon's best Plan objectives, including many of the CF and CFN Plan Achromats. (And its use is not limited to the old, black S-series either, as it works quite well on a number of more more stands as well, including even some non-Nikon scopes, such as the Olympus BH-series – assuming a proper mounting adapter is used.)

Note that the images below were created simply to demonstrate some typical IPC system image color possibilities and so may not be truly representative of its resolution capabilities…  (Click on image set below for larger versions.) 

Note that focus has been altered very slightly between above images to emphasize different details. 

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Secrets of the AO Polanret System – Part II.

Note: This is an interim release. Because of the total length, Parts I & II are planned to be combined into a single document, with additional photos, as a .pdf file. This will allow continued online viewing as well as easier download and (if desired) printing. 

For Part I, see the post of January 28, 2017, below. 
For sample images, see the post of February 7, 2017. 

Part II

To understand a system like the AO Polanret, or, more specifically, to understand the need for it, you have to recognize that the Phase Contrast technique is primarily affected by just two characteristics of the observed specimen: Refractive Index (RI) and the Thickness of the specimen. (Refractive Index is merely an expression of how much light is slowed by its passage through a material. As an example, for Water, the RI = 1.333 – meaning that light travels only 1/1.333 as fast through water as it does through Air, RI =1.000.)

The basic appearance of Phase Contrast image depends upon the difference in RI between the specimen and the surrounding material. Since nearly all biological material has an RI greater than that of Water, the various components of a specimen in Water will typically be displayed as darker than the background.

However, this is only true for phase objectives of the Dark (or Positive) contrast-type – the most common type. For objectives of the opposite type, Bright (or Negative) contrast. the specimen and its details will typically be brighter than the background.

Now, while all that may seem quite simple, in practice things are not always so straight forward…

If, for example, cells are in a culture medium which has an RI that is nearly the same as the cell bodies, then the level of contrast provided by normal phase objectives (typically, "Medium" contrast) may be inadequate. This is because, if the RI difference between the specimen and is surrounding medium is low, then the contrast level will also be low, and so an objective of higher-than-normal contrast may be required to show the specimen properly.

However, under the same circumstances, consider what happens when the internal contents of the cell are examined. Here, the minute bodies of interest (e.g: cell nucleus, or its contents) may well have an RI that is quite different from the surrounding cell material. In fact, due to the normal variations in RI within the cell, the potential image contrast levels can easily vary quite widely from location to location.

This means that the ideal contrast characteristic for the phase objective can easily vary as well.

If the objective contrast is too high, then details may be obscured, and, if the objective contrast is too low, then some details may not be visible at all. Thus, for the most effective observation, the objective's contrast characteristic might best be made variable, such that the user could adjust it as necessary for each specific observational situation. This is the premise for the AO Polanret system (and similar "Polanret" type systems).

To examine this point further, let's consider a case perhaps more familiar to many users… 

Consider, now, the use of Phase Contrast on "mounted diatoms."

Historically, these specimens (RI=1.46) have been mounted in media of high RI (RI=1.72, or even higher). This was done to improve the visibility of the delicate markings on the specimens, a technique dating from long before Phase Contrast was invented.

However, when viewing such mounts with Phase Contrast we have two undesired effects: (1) the RI relationship between the specimen and the media is "reversed" (e.g: RImedia >> RIspecimen), and, (2) inherently high contrast within the mounted object.

Now, the first issue results in an "reversed" phase image (e.g: when "Dark" type objectives yield a "bright" image), and the second issue often results in a "phase halo" that may easily mask the very details being sought! These issues have led some makers to seek technical solutions (such as "B minus contrast," or other specialized-contrast phase objectives) in an effort to achieve a more acceptable image. (Another, frequently-used alternative is to simply abandon the use of Phase Contrast altogether, and opt instead for a different method, such as COL or Oblique Illumination.)

But, with a Polanret system, the user only needs to adjust the controls so as to "dial-in" the most appropriate levels of Amplitude and Contrast for the particular specimen at hand!

All this now brings us to the point of discussing just how these changes are produced by the Polanret system…

Actually, there are two main sections involved – an "image transfer" (or, "relay") optical system, which shifts the objective's rear focal plane into the optics of the Polanret system, and a Phase processing system which permits optical manipulation of the images from the objective, based on phase differences.  

Also, understand that there are actually two images formed by the (any) objective: 

  

(1)  the Intermediate Image, which is located near the eyepiece and forms the actual image of the object, and, 

(2)  the Rear Focal Plane image which, in this case, holds an image of the Phase Condenser's annular ring. 

In an ordinary Phase Contrast objective the Rear Focal Plane is also the location of the Phase Plate which is responsible for determining the characteristics of the final Phase Contrast image. But, in the Polanret system which uses non-phase objectives, this plate is not there. Instead, it is positioned inside the Polanret unit where the system's optics "relay" the necessary Rear Focal Plane image to it. 

Now, the Phase Plate in the unit (typically, one for each objective magnification) differs from those found in ordinary Phase objectives in that it is comprised of a pair of concentric rings made of polarizing material. These are arranged such that, when placed between a Polarizer and Analyzer, rotating the Polarizer will darken one ring or the other, selectively. This feature allows adjustment of the Amplitude characteristic of the system. 

This plate is followed by a quarter-wave plate and adjustable Analyzer, which allow varying the Phase Shift ("Phase change" sensitivity) of the system. Thus, both of the important characteristics of the system are made user-adjustable  and the user may select and degree of Bright or Dark contrast, or any degree of phase change sensitivity within the system's limits.  

Note that the unit's optics are arranged such that the Intermediate Image is unaffected by these operations, except for the addition of Phase Contrast information to the final image. 

So far, so good – but now it's time to consider Reality!  

In order for all of this to function properly, certain operating conditions must be met:  

   

  (a) The objective to be used must be precisely positioned relative to the matching Phase Plate in the unit. This means that the objective must be almost exactly concentric with the Plate, and the image of the Condenser Phase ring in the objective's Rear Focal Plane must be almost exactly the correct distance from that same Phase Plate in the unit.  

   

  (b) Now, the objective's concentricity is controlled by mounting of the Polanret unit to the microscope  body (over which the user has little control – this is mostly a matter of manufacturing tolerances), AND the centering adjustment of the microscope's nosepiece (which the user can control, somewhat). However, the nosepiece centering needs to be accurate within a fraction of a millimeter, if the centering function for the Condenser Phase Rings is to have the proper effect.  

   

  (c) The distance of the Phase Ring image (in the Rear Focal plane) is controlled by several factors, the design of the Phase Condenser and the Phase Rings being largely beyond user control. (The exact focus of the Condenser is under user control, but has only minimal effect.) Phase ring centering is, of course, under user control, as above. 

   

  (d) Surprisingly, what is critically important is the adjustment of the microscope's stage height! This is because with AO's nosepiece focusing, the stage height is what determines where the objective will be positioned, relative to the Polanret unit, when the object is in focus – and that is the only point that matters when considering the location of the objective's Rear Focal Plane! If this height is off more than a millimerer or two, then the image of the Condenser Phase Ring will not be in the correct position within the Polanret unit. 

   

  (e) You need a whopping amount of light to run this thing! The use of Polarized light technology within the unit exacts a rather severe penalty in terms of light throughput. The Series H10 scope boasts a 20Watt Halogen illuminator, which puts out roughly 400 lumens. That is barely adequate for the system in its most transparent modes. But, if you expect to run the unit in more "normal" modes you simply need more light!

The H20 (and 120) microscope models feature illuminators based on 100 Watt lamps – good for about 3200 lumens (if you pick the right lamp). This is just about sufficient to run the unit properly, but can be a bit marginal if there's a beamsplitter in the image path (as for photography) and/or a moderately dense color filter in the illuminating path (to reduce color artifacts from the Planachromat objectives, for example). 

And as entertaining as all this might seem, it gets even more so when the job includes aligning the basic microscope from scratch and working without access to the proper Condenser… 

So, taken all together, it is now easy to see why AO recommended against using anything but a factory-aligned system. 

There is no known documented procedure from AO to allow users (or even AO dealers) to make all the necessary adjustments to permit the Polanret system to operate as intended – although a practical, user-level system alignment procedure is currently being developed by this author.

Despite its complexity, and minor issues, the AO Polanret stands as a potentially useful analytical instrument. However, it does not stand alone as there is another Variable Phase Contrast system out there – as you will soon discover – and one which promises much more colorful results! 

* * * * * 

Looking Forward -- beyond Polanret?

As we prepare to wrap up the discussion of the AO POLANRET system some of you may begin to wonder whether that device is just one-of-a-kind, "oddball" invention, or whether there may be other, similar instruments lurking out there, perhaps by other makers?

Perhaps the image panel below will give you a clue…

Stay tuned to this Blog for answers!  

(Click on the image panel above for larger versions, then use the Return or Back button in your browser to return to this page.) 

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Images from Polanret!

As efforts continue to shift this Blog into more visual presentations, here two sets of images made from a single diatom at random setting for the instrument.

The in the first set, immediately below, colors from the camera images have been left largely intact. However, note that the colors are, to some extent, due to the interactions between the residual phase information from the instrument and the internals of the digital camera, and are not present to the same extent in the visual images.  (Such effects are common in phase contrast imaging and are not peculiar to the Polanret. They may. however, vary somewhat with the specific camera used, in this case a Canon 2400is.)

The next set contains exactly the same images as above, but with the extraneous color information suppressed. This provides a better representation of the actual visual appearance of the specimen.

This set more clearly demonstrates both the Polanret's ability to vary the image contrast level continuously and the ability to switch seamlessly between Bright and Dark contrast modes. (Click on an image set for larger versions, then use the Back button in your browser to return to this page.)

A more technical discussion of the Polanret system will follow in a day or two… 

Also, see the Blog Post of January 28, 2017 for an earlier discussion of this system. 

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Secrets of the AO Polanret System – Part I.

I wasn't going to write this piece, at first, but after discovering just how little information there was on this system, I reconsidered. Although the equipment itself seems to be extremely rare, nevertheless, there is much to be learned from simply reviewing why it was created, what it does, how it does it, and how this may actually be useful – even if only as an educational tool. In Part I, we cover the Background and History of the AO Polanret system, and reveal some of its failings. In Part II we will examine the underlying technology and consider what these units may still have to offer. 

(Naturally, the opinions expressed herein are those of the author, based on the very limited amount of published material available on this topic, and based on actual use of the system reviewed.)

Once upon a time (late 1940's - early 50's) Phase Contrast was the latest wonder of Microscopy, allowing easy visualization of living material – and by purely optical means! It seems like the perfect answer to issues such as whether new, minute structures in cells were naturally-occurring components, or merely artifacts resulting from the various chemicals typically used in the often-tedious and technically difficult sample preparation process.

Phase Contrast appeared to offer a powerful and relatively inexpensive means to observe cells in their natural state, free of chemical treatments and all the skills and technical labor accompanying them. To the folks running AO/Spencer back then this must have seemed like a perfect opportunity to carve out a niche for the Company and even make a name for themselves in this emerging technology. And so, they began their long journey down that road…

Now, back in the early 1950's AO did basically succeed in this endeavor. They certainly made large investments in Phase Contrast technology and produced more different types of Phase Contrast objectives than anyone else – some of which were never duplicated by anyone else, either (e.g: the "B minus" and "A plus" contrast types.)  Unfortunately, their Series-2 and -4 microscopes were not greeted all that warmly in the marketplace and this proved to be a weakness in their grand plan. But, in addition, there was not a great deal of interest surfacing in all their various, "special" types of objectives – perhaps because AO, back then, offered only Achromat objectives for Phase Contrast..

So, in response, AO began considering solutions, including a switch to "infinity" optics and Planachromat objectives, and, perhaps replacing their rather undistinguished 2/4 models with something better. And then the bomb hit! 

Nomarski described a new, very different system, based on something called "Differential Interference Contrast,: or, more simply, just "DIC". And, unlike Phase Contrast, Nomarski's new DIC system did not inherently require special objectives and, in addition, offered the promise of even better image quality!

DIC did not require re-desgning objectives and so could (potentially, at least) be easily applied to existing systems, using existing objectives – potentially even Apo's and PlanApo's! So, researchers given, a choice between buying AO's Achromats (for Phase Contrast), or of simply re-using their existing, very expensive Fluorite and Apo objectives, naturally opted for the Nomarski DIC system.

And, with the emergence and growing acceptance of the Nomarski DIC system, the glaring faults and limitations of the older Phase Contrast system became all too apparent.

For example, one of the bigger problems with Phase Contrast was the appearance of "halos" surrounding objects and even some of the internal structures in specimens. Part of this was inherent in the system, but the problem was amplified by the limitations of the optical technology of the day, which limited the actual performance of the objectives.

But, another serious issue was that the contrast characteristics were fixed within each objective, and so, to change these meant replacing the entire objective. Thus users were often faced with needing full "sets" of different types of phase objectives, usually mounted on interchangeable nosepieces to allow rapid switch-overs.

All these extra costs only elevated the price of Phase Contrast to users, and made the superior Nomarski system appear even more attractive. (Note that, in the Nomarski system, contrast characteristics are basically just a simple optical adjustment, with no need to change or even move the objective in use!)

The answer, it must have seemed, would be to "externalize" the Phase Contrast mechanism with yet another piece of equipment. This, at least in theory, would allow users to achieve Phase Contrast results using existing (non-phase) type objectives, while also permitting direct and continuously-variable control over the phase-optical characteristics.

Now, while the basic Concept seemed like a terrific solution, the ultimate Reality was something quite different. And, to be perfectly honest, not all the blame should fall on AO's shoulders.

"Polanret" type systems had been known since the early days of Phase Contrast (ca.: 1947) where they had been described in scientific literature. In fact, a number of variations of the basic concept were described in subsequent years. However, all of these systems employed Polarized light in an arrangement where it could be controlled (adjusted) to vary the characteristics of one or more "phase plates" within the system. Further, an optical system was used to effectively shift the "rear focal plane" of the selected objective into the system, where it could be manipulated as desired.

Of course, all this "accessory" optical technology was not without its own costs, and complexity, and it was not until the 1970's when evolving optical technology actually made them practical. Yet, even when they finally did become commercially available, they failed to displace the then well-entrenched Nomarski DIC system, and they were largely ignored by the marketplace!

To better appreciate this, we merely need to look at some of the practical limitations of AO's Polanret system… 

First, it should be stated that AO only sold their system "married" to a specific microscope! In fact, you could only but their Polanret system as part of a package which included a new, expensive H20 (or, later a 120) instrument. Further, even if you already owned the correct model of AO microscope, there was no way you could simple "add" the Polanret unit to it – this could only be done at the AO factory, and only on a new instrument. (The result of this was to effectively double the price of the AO system!)

But, wait, there's more…

Apparently the alignment between the Polanret unit and its host microscope was so critical that customers were warned (even in AO's sales literature) not to try to transfer their Polanret unit to any other instrument, even if it was identical to the one originally used. But that is not the worst of it… 

AO's Polanret system was strictly limited to just four AO Planachromat objectives – all just "clinical grade". And, surprisingly, the one objective with perhaps the greatest appeal, their 50x/0.80 (oil) Planachromat, was never included in the system… not even as an option!

So, after a great deal of time and effort spent creating their Polanret sysyem, AO totally dropped the ball by making it ridiculously expensive and then restricting it so severely as to make it nearly useless in practice!

Finally, shortly after the AO Polanret system came to market Zeiss offered their DIC system at a similar price, only to be followed by both Nikon and Olympus introducing their DIC systems, at lower cost, shortly thereafter.

Upgrading their Polanret system to the newer AO 120 microscope did little to change the basic equation – the Polanret was just too little, too late, and too expensive for what it did!

Today, given that the system included a special phase condenser (Cat. #2110), and the fact that the various pieces were most likely separated over the years, it seems quite doubtful that there are any complete, fully-intact AO Polanret systems remaining in user's hands, anywhere!

And, as a final, ironic note, the AO 50x oil Planachromat (mentioned earlier) works just splendidly on the system…AO simply never bothered to sell it that way!

In Part II we will examine the technology of the AO Polanret system and consider what these units may still have to offer today's users… 

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AO Polanret -- the Saga Continues...?

As things continue to move forward here, albeit, slowly, it seems that a little good news might be in order…
 
The unexpected appearance of the little-known AO Polanret unit at first seemed just another distraction; one more delay in completing the long-awaited Water Immersion piece.
 
However, some experience with the unit, plus methodical investigation of its workings, led to a surprising discovery – the unit actually works under water (well, more exactly, it works just fine with Water Immersion objectives)!
 
The net result is that the Polanret unit has the capacity to convert ordinary Water Immersion optics into a wide range of Phase Contrast types, simply by manipulating the controls. You can choose between Bright and Dark contrast, choose the level of Contrast, and even select the most effective level of Phase Shift for the particular object being observed.

So, in effect, instead of being handicapped with a very limited selection of phase types, with this device you can easily just "dial-in" whatever combination of characteristics seems to work best, from a range of something like over a hundred possibilities – truly, an "Experimenter's Dream"!!!
 
Of course, it also works well with a wide range of ordinary "dry" type objectives, too. And, as all this is "done with mirrors" (plus some optics) the selected objective can be easily and instantly switched back into its normal operating mode, if desired. Furthermore, no physical modifications of any kind are required to the objectives to be used.
 
Now, although the unit was designed to work only with Infinity type optics, it has been shown that it is also capable of performing its "magic" with a fairly wide range of finite objectives as well. So far, testing with Water Immersion has been limited to the LOMO 40x/0.75 Achromat and 70x.1.23 Apo, with both types tested successfully with and without using a coverslip and, of course, Water Immersion.
 
The next step, as soon as time permits, will be to integrate a photo port for a digital camera to permit recording some of the actual test results. Then we may see just what kind of images our "Magic Phase Contrast Machine" is capable of…

There's nothing quite like a set of impressive [hopefully] color photos to help liven up a stale old Blog! 

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Shown above: Schematic of the AO Polanret Optical System (reproduced from AO Polanret brochure):

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Water Immersion -- Under water, or not? & AO 'Polanret'...

The long-awaited presentation on 'Water Immersion' is alive and well.

However, in the intervening weeks since it was last mentioned, it has morphed into an entirely new form.

First, considerable information has been developed about entirely new techniques, covering both optics and methods.

Second, this new information has prompted a slight re-direction, from the rather narrow topic of 'Water Immersion' to the broader, and probably more useful, topic of  'Microscopy of Objects in Water.'

Third, the overall presentation has been re-oriented toward stressing the more practical aspects of the topic, with theoretical considerations largely deferred to some future time.

Why the delay? Admittedly, the older I get the less thrill there seems to be in writing, and the more interest there is in actually doing things. This attitude has prompted considerable experimentation into extending and improving some existing methods, both to increase usefulness and improve the quality of results.

But, wait, there's more... 

To be perfectly honest, there's nothing quite like getting a new 'Toy' for the New Year – in this case one of the rare, and perhaps only, surviving example (in working condition) of the mythical AO 'Polanret' variable phase contrast system! (Of course, minus any useful documentation -- like, instructions!)

A creature of the 1970's, it has taken decades for me to track this down. Now, I finally have one…

And, slowly, I have been able to discover a few of the 'lost secrets' of making it work!

The only known AO documentation on this device is the sales brochure (ca. 1976), which has been replicated in .pdf form, from photos of the individual pages, and may be found here:

 AO Polanret brochure

The problem now is, whether to simply use this extraordinary machine for the relatively mundane tasks I might have for it, or is it better to pass it along to a collector or technician who can best appreciate and/or properly care for it? I certainly would hate to see this rare find end up at an estate sale someday!  

The current setup being used for evaluation is depicted below: 

Personally, I am more interested in seeing this unique device move into proper hands than I am in making a real profit on it. (And, I am strongly dis-inclined to start tinkering with the innards of such a device.)

So, I am certainly open to suggestions on a possible new home for this remarkable 'orphan'... (Polanret unit for sure, microscope optional.)

And, naturally, I am open to discussing a possible swap (for microscope stuff, of course) ...

If you have any interest, or can provide any relevant Polanret info, please e-mail me at:
 bettermicroblog@gmail.com

Thanks!

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