The Bausch & Lomb Micro-Tessar

At times it seems that for every field that makes use of a light microscope there is a specialized stand. If not a particular stand, then an outfit of unique accessories. At the very least there’s optics for every occasion. A Bausch & Lomb Micro-Tessar objective is one more.

Just as photographers are wont to speak about portrait lenses when they mean Petzval’s so too are photomicrographers stage-whisper secretive when it come to Tessars. Although, a photographer who’s worked in a chemical darkroom is apt to know the Tessar as well, it frequently finding a place on the business end of an enlarger, for many a photomicrographer it is all too unfamiliar. Everyone knows about Flourites and Apochromats, even the utility of green filters for achromats, rather less know of Tessars.

A discovery of Zeiss, and therefore found in the Bausch & Lomb catalog only after the Triple-Alliance era, a Tessar lens is composed of four lenses (two each of crown and flint glass) with an aperture diaphragm between the first two lenses (which are separate) and the final two (which are cemented together. It’s an exceptional lens. With excellent correction for spherical aberration, a Tessar is likewise well corrected for color and astigmatism, which is to say it’s magnificently flat at even the lowest equivalent focus. A Micro-Tessar is such a lens outfitted in the RMS (society) thread. Although, B&L includes the LTM (M39) 72mm Teassar lens in their catalogs under the same designation.

Through the unimaginable generosity of a dear friend and member of that loose organization that is the community of microscopists a fine example of Micro-Tessar has been added to the collection. It’s a 48mm Micro-Tessar and though in need of a little cleaning quite irresistible. Here’s a few scans of negatives exposed just this past evening on the only film that wasn’t in the freezer (Ultrafine Xtreme 100) run through some Diafine that happened to be at the back of the shelf—a poor choice for a budget film but sure to compensate nicely for over or under exposure.

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Young Pipe Fish, Bright-field, cropped

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Young Pipe Fish, Dark-field, cropped

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Head of a Blow-fly, Bright-field, un-cropped

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Head of a Blow-fly, Dark-field filter, cropped

In spite of the rush with which the above were produced, without an objective, and using a desk-lamp and mirror with no condenser, observe the above. The field of view on the first image is in excess of 9mm. That blow-flys head is 4500μm and this lens has oodles of dust on it. Only unavoidable scheduling conflicts prevent giving this lens the attention it deserves…

Library Update

I’m currently in the process of revamping the Bausch & Lomb manual and catalog library in an effort to make the documents more useful. To begin with each document is going to have searchable text embedded in the PDF. This wont have any real impact on the readability of the documents (unless of course one is using a reader which supports direct viewing of embedded text) though it will allow for one to copy and paste from the file. It will also, and this is the primary motivation for the effort, allow for one to search the document.

It’s a slow process and requires some significant time for each document. Thankfully, once it’s done it’s done and the files will be more available than ever as search engines and web-crawlers will begin to read the files and begin offering them up among the results of ones favorite search engine.

As the effort progresses the format of the existing library page (and it’s current files) will remain unchanged. Instead the new documents will be placed on an alternate library page with an entirely text based format that will not involve squinting at 100 pixel wide thumbnails.

Amateur Photomicrography IV

The setup for photomicrography can seem complicated. In fact it’s quite simple, and one already knows everything involved; provided of course there is some familiarity with the visual use of a microscope. Visually one need only place an object on the stage, direct the illumination of the light source, rough focus based on the objectives working distance, and move ones eye to the eye-point of the ocular. That done, adjust for fine focus and enjoy.

With photomicrography a camera is substituted for the eye. If the camera happens to have the precise optical characteristics of the operators eye then fine focus may be obtained visually and translate without adjustment to the camera. Otherwise the focus can obtained by some other component that duplicates the characteristics of the camera. In theory it’s simple. In practice—particularly if time has not permitted the fabrication of a coupler—switching from the focusing tube of the Kodak No.0 photomicrographic outfit to the camera is a recipe for vignetted images. Wouldn’t it be nice if the camera itself could serve for both focusing and photographing?

It absolutely can and it’s now the only method this technician would recommend if not using an integrated camera system!

Permit me now a lengthy aside not at all written in my usual, tedious, arms-length style. I had never before considered using sheet film in a box camera, honestly, never! Reading through the B&L Amateur Photomicrography manual I saw the words “use cut film” and about lost my mind. Cut film! It’s so obvious! I’m not a skilled photographer and as such am not prolific—more’s the pity I’ll take forever to get any good. As such I might go weeks before shooting the last of even an 8 frame roll of 127, and even longer as I stress way too much over exposure and generally end up with endlessly bracketed frames. But with sheet film! NO WORRIES! 

It turns out sheet film is expensive, a dollar or more for B&W 2-1/4 x 3-1/4, Well, buy 4×5 and cut it down in pitch black! IN PITCH BLACK?! No thank you, I’m enough of a klutz with the lights on. But wait, X-Ray film is orthochromatic? X-Ray film is $20.00 for a pack of 100 5×7 sheets?! A single sheet will cut down to 4 of the slightly less than 2-1/4 x 3-1/4 frames that will fit in Kodak No.0 which means I get sheets of film I can work with under red light for $0.05 a frame! So, yeah, I’m all over that!

Using orthochromatic film would have been easy in the time when the B&L Amateur Photomicrographic outfit was new, today it’s a bit of a wait to obtain film as it will nearly always need to be ordered from a medical X-Ray supplier. With film in hand and all in a changing bag or darkroom remove a single sheet to be sacrificed. Use that sheet to trace out the size of a frame which will just fill the film plane of the camera, and cut it out carefully. Once the size is perfect a method of safely cutting down the film under a dim safelight will be needed. To that end obtain a guillotine paper cutter. Lay the cut down sheet on the cutter and align the long edge with the blade. Then put down a length of white (or otherwise highly contrasting) tape aligning that with the edge of the film farthest from the blade. Repeat lower down from the taped guide for the short edge. By this means a full size sheet may be speedily cut down to precise dimensions in the dim safelight (or total dark if sufficient care be taken).

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Model R arranged for photomicrography

In a dark room (for simplicity) one should arrange the microscope so it be secure (rubber bands wrapped about the foot will give the Model R a firm grip). Further bands may be used to secure it to the base of a ring stand if one be employed. The arrangement shown at left illustrates the method described. For illumination any handy source may be employed, though it is advisable to use as a source something well baffled which will not permit stray light to fill the working area. Stray light is less a concern when working with roll film but for use with cut film it should be well avoided if at all possible.

Working in subdued lighting one may open the rear of the camera and use a sheet of cut (but exposed to room-light and undeveloped) film as a focusing screen with the shutter held open. Place the film in the back of the camera and carefully arrange the camera over the eye-piece. Turn on the illuminator and make adjustments as required for alignment of the whole apparatus.

When all is well positioned turn out the room light and illuminator. If working with orthochromatic film one may turn on a safelight. Place a sheet of unexposed cut film into the camera, taking care not to move at all the camera or focus of the microscope. Turn on the illuminator and trip the shutter of the camera. Working as just described will likely result in blurry images due to camera shake. Rather than more securely arranging all the elements one may simply leave the cameras shutter open and control exposure by turning on or off the illuminator or placing an opaque card into the light-path.

The images above were enlarged onto Fomalux silver-bromide enlarging paper from X-Ray film negatives which were exposed using the Kodak No.0 Amateur Photomicrographic apparatus and Model R microscope from B&L. The issues seen in the thin section (lack of uniformity in lighting) is from a processing defect (uneven development) and is present in the negative. In all of the above images the obstruction of  illumination was used in place of the cameras shutter and the front element of the microscope objective on the Model R was removed.

The resolution of the diatoms in the image at left is far better than one could have expected from a “toy” microscope. No doubt the impeccable condition of the Model R contributed significantly. It’s worth noting as well that without a meniscus lens (as would normally be found in a Kodak No.0) only the Model R’s well-engineered optics were able to affect the image. One is certain to find significant loss of resolution if working with a Kodak No.0 (or other box camera) that has a meniscus lens.

Amateur Photomicrography III

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Photographic Kodak No. 0 (left) and Photomicrographic Kodak No. 0 (right)

The Bausch & Lomb amateur photomicrographic outfit is built around a Kodak No. 0 Brownie 127 film box camera. Before getting into the process of actually using it, it might do to look at just what is different between the photomicrographic No. 0 and the standard No. 0. Apart from the addition of a focusing telescope and a stand-clamp the only difference is purely optical. While in the off-the-shelf No. 0 the camera is equipped with a simple meniscus lens, the photomicrographic No. 0 is completely free of optics in the image forming path.

With a modern professional photomicrographic apparatus there’s certainly going to be some optics in the photomicrographic light path—more about why in a moment. This most often consists of a focusing relay lens system, usually in the form of a reducing series .7x or .5x being the usual magnification factor. This reducing series may additionally include lenses for the correction of spherical aberration (as in the BalPlan or flat-field DynaZoom/Dynoptic). In standard achromatic systems the system is free of such correction optics and may well consists solely of a beam splitter, or reducing lens only.

The reducing factor of such systems is, somewhat confusingly, sometimes found coupled with a body tube labeled anywhere from 1x to 10 or even 15x. The two portions work together and serve to provide a cropped frame that is then enlarged to fill entirely the film frame. In third party “eye-piece” cameras this crop factor was accomplished by quite inferior optics (if any at all). The reason such a reduction is necessary is owing entirely to the small size of what’s become the standard imaging surface. Currently, that’s a CCD or CMOS sensor somewhat smaller than a 35mm film frame. Where film photomicrography is still pursued, or was prior to the great digital migration, that nearly always meant a 35mm film frame. It bears remembering that 35mm film is a “miniature” film format—no matter how many folks tout their “full frame sensor” camera—it’s still miniature, which means reducing the image forming cone of light to get something near to the optical field of view in the frame. Early photomicrography used large format film and handled cropping with long bellows extensions.

With no optics in the camera, and a box ‘bellows’ of three inches, the No. 0 can be expected to offer almost no crop factor at all. This is functionally a good thing. By greatly restricting the ‘bellows’ enlargement chromatic and spherical aberration present in the simple optics of the Model R are prevented from revealing themselves (as they surely would be at greater enlargements).

The other significant upshot of an lensless camera is the practical impact on focusing. With no optics to worry about the system that is employed to focus the camera is made more simple. To duplicate the focus of the camera one need only use a device of identical length with a ground glass at the imaging surface. In the Photomicrographic No. 0 that is a tube one inch in diameter with a circular ground glass at the far end. Although the ground glass is much smaller than what one must expect the film to capture it certainly enables accurate focusing. One must ensure the primary feature of which a photomicrograph is desired is centered, and hope for the best.

In a complete system there is a further component, a circular bushing (also void of any optical components) which fits one end over the Model R’s ocular while the other end inserts into either the focusing telescope, or No. 0 as required. It should be a simple matter to drill out a hardwood dowel as a fabricated replacement. With that knowledge, the reason for the unique aspect of the shutter opening on the photomicrographic No. 0 becomes apparent. It is constricted as it nears the shutter mechanism (while the standard No. 0 is wide open) because the bushing must be prevented from pushing too far in and obstructing the shutter mechanism.

In use then, one would attach the photomicrographic No. 0 to a ring stand with the Model R held steady underneath. The camera may then be rotated such that the focusing telescope is over the ocular while the a slide is positioned and brought to a clear focus. The camera may then be swung into place and the shutter tripped for either an instantaneous (snapshot) exposure of the time bar may be pulled out if a longer exposure is required.

 

Kodak No. 0 Box Brownie Digression

The oddity of 127 film is not so much owing to the negative size—sure it’s smaller than 120 and bigger than 135, but to the lack of sprocket holes. This characteristic has a significant effect that is apt to go uncommented even when it is recognized. Without sprocket holes the cameras are mechanically much more like medium format “red-window” cameras than either 110, 126, or 135 film cameras. Red-window cameras are far simpler mechanically than other film advance types.

Where 135 cameras take advantage of the films double sprocket holes and by the use of a gear system count the distance the film has advanced with each stroke of the advance lever, turn of the knob, or activation of the motorized advance, red-window cameras require the active attention of the camera operator. When loaded with film a red-window camera permits a view of the films backing paper. A standardized system of numbers on the backing paper show through the red window and thereby indicate the position of the film in the camera. When the advance knob is turned one numbers moves from the window and is replaced by the next.

Some cameras have a single red window and the progression is simple. By turning the knob 1 progresses to 2 and on through the total range. Other cameras may feature two red windows and the operator should then use both. When 1 is displayed first in one window, the shutter is tripped to take the first photo. The film is then wound on until the 1 shows in the second window. At this point the shutter may be tripped again for the second photo. The same process is repeated for the complete range.

In cameras making use of two red-windows the total size of the negative is restricted to half of the total size of the largest standard frame size. Such that for 120 film a 6×9 frame is reduced to 6×4.5 or in 127 a 4×6 frame is reduced to 4×3. The Kodak No. 0 Brownie is a single red window camera and captures 8 frames in the 4×6 format. Although a fundamentally obsolete format (even if it is still manufactured) 127 film and the 4×6 frame size are small enough that a photographer can often use a 135 negative carrier for (admittedly severely cropped) enlargements or a 6×6 120 negative carrier with an improvised mask for un-cropped enlargements. Not having to purchase a unique and hard to find negative carrier is a great boon to anyone working with 127.

On the topic of specialized equipment, one is apt to feel the need of a new developing reel. Although many of the common and currently manufactured plastic tanks and adjustable reels are able to handle 127 (as the adjustable reels are still equipped to take it despite it’s comparative obscurity) anyone favoring steel tanks and reels is apt to face a long search for a 127 reel. At least this only applies to those who must use daylight processing tanks. Those with access to a dark room may use the old roll-film standby of the open-tray loop.

In the field anyone accustomed to working with box cameras is apt to notice primarily the diminutive size of the Kodak No. 0. Those for whom the No. 0 is an introduction to box cameras are liable to feel quite the opposite. In either case one thing that is quite small are the viewfinders which are of the frosted window, lens-and-mirror type. However small the two (one in portrait and one in landscape) may be they are usually preferable to the wire-frame type that require the camera be held at eye-level. Holding a camera is a practiced skill and those unaccustomed to it may struggle to obtain clear photos with the quite slow shutter speeds of old box cameras. Needing to hold the camera to the eye only complicates the task.

Still, like all the box Brownies the No. 0 is a breeze to use. The simple flip-flop shutter is unlikely to ever fail and although the camera itself is small the winding key is full-sized and easy to turn. Equipped as it is with a pull tab for timed exposures one may wish to use it on a tripod only to find the No. 0 not offering a tripod socket. Thankfully, it’s small size mean it is easily fit into any of the common and inexpensive cell-phone tripod mounts. Take care though, the minimum focus distance is around 5 feet.

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Birdhouse on 127 size Kodak BW400CN

 

 

Amateur Photomicrography II

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Kodak No. 0 Brownie and 127 film

The Kodak No. 0 Brownie box camera is not currently in high demand, doubtless owing to it’s use of 127 film. So-called “cartridge” film, 127 is a 1-3/4 inch wide, 23-1/2 inch long unperforated roll film. It seems strange to describe it in terms of inches but honestly, using millimeters in this case is rather confusing as the film was designed using imperial units rather than metric. Somewhat confusingly it is not incased in a cartridge or cassette despite it’s colloquial moniker, rather it is wound on a spool with numbered backing paper in the style of more common (nowadays) 120 film. Cameras using 127 film are frequently seen in one of two frame formats, either the square 1-5/8″ (4 cm) or rectangular 1-5/8 x 2-1/2 (4 x 6.3 cm) produced by the Kodak No. 0 Brownie.

For a time in the mid 90’s the 127 film format was no longer in production by the major photographic houses. It continued to be available from specialty sources or as expired film on the used market. In general even the expired film cost in the area of $10 USD roughly double the significantly larger (and continually manufactured) 120 film format. Although currently a number of manufacturers have revived production of 127 film it is still generally in the $10-$20 USD range for a single roll. For that reason anyone wishing to pursue photomicrography with the Kodak No. 0 Brownie (or photography in general with a 127 film camera) would do well acquire only a few rolls and saving both the spools and backing paper.

Provided a supply of 127 spools and a numbered backing paper or two (though the paper could be fabricated from any light-opaque paper stock) one can easily and cheaply produce 127 film for personal use. The easiest method would be to simply spool a length of 135 film (standard 35mm film) onto the 127 size backing paper. Regrettably, 135 film is perforated and between that and the fact that it is already 10mm narrower than 127 film much of the frame will go un-captured. A better option is to begin with an unperforated film wider than the 127, 120—being nominally 60mm wide—is an ideal choice, and slit it down to the 127 width.

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Simple film slitter

The above diagram of a film slitter may be used to slit one film width to another and can be with a few simple changes so constructed as to slit any desired width from any other. The basic rule of construction is that the film path must be of the width which is being slit from (the widest films width). In the crude diagram A is a block of wood of just over the width of 120 film. On either side of this are attached guides B which are additional blocks of wood which rise a short distance over the bed of block A. The position C is a groove cut into block A into which has been inserted a utility razor. The figure to the right shows this in profile. One further piece is needed, block D, which is the width of A and has a wide cut at location E into which the razor is able to slide without making contact with the wood. This channel covers the blade so it is not exposed while slitting (which must be done in total darkness) and allows block D to hold the film down such that it is slit by the razor rather than passed over it.

 

 

Amateur Photomicrography

Bausch & Lomb in it’s finest incarnation was based in a large upstate New York city on the shores of Lake Ontario called Rochester. At the time it was The Flour City, so named for the many mills along the Genesee river which ground the wheat towed into the city by that turn superhighway of historic New York, the Erie Canal. Now, The Flower City is remembered less for the great optical firm of B&L and more for the once mighty company of another golden age optical company, Kodak. Even today the George Eastman house is at once one of the most well appointed and well respected museums of photography in the world, host every year to dozens of programs and feature presentations.

It should be no surprise that microscopy and photography should intersect. That two of the greater names in each field should call the same city home is surprising, but perhaps less so when one considers that the two would have been attracted by the same resources. B&L made optical instruments and components of all sorts, and no small variety of microscopes. The Eastman dry-plate Co. (later Kodak) made dry photographic plates and film, together with the low-cost cameras which would create a demand and market for their more profitable consumable products. With the two companies calling the same city home one could expect that the Kodak cameras and film would be sure to see use at the eyepiece of B&L microscopes.

Amateur Photomicrography

That B&L should have published a manual specifically treating with one of the early Kodak box cameras is only natural. It’s this manual we’ll be looking at in the next few posts. Chances are good anyone in the United States of America knows someone who has an old Kodak box camera laying around they’d be happy to make a present of. Otherwise pick up a Kodak Brownie No. 0 to work with the B&L model R and follow along with the manual or pick up the larger Kodak Brownie No. 2a to work with a full size B&L microscope.

B&L Model R and Eastman Kodak Brownie No. 0

B&L Model R and Eastman Kodak Brownie No. 0

The Model R1900: part 2

In 1964 there was a very real chance that a few children who had grown up with a B&L Model R in the house were setting up to begin their careers in education or finding themselves parents. Even in those comparatively recent days microscopy as a pursuit and optical companies in general were not what they are now. This was certainly not the boom period for the optical industry, but rather, it’s maturity.

The myriad firms on the continent, the island of Great Britain, and in the United States were consolidated. Spencer and American Optical had become AO Spencer. Smaller firms like Gundlach (later dissolved in 1972) had moved into other fields or drastically contracted their efforts. The Triple Alliance was dissolved a generation previous and with Saegmuller long dead Zeiss and B&L found themselves giants in their fields.

B&L, with military connections begun in the first and strengthened further by the second World War looked to expand in new markets. Their institutional arm sold to professionals of all stripes from the machines to the physicist, MD’s and DVM’s had B&L stands on their benches either those inherited with their practice or purchased new from  salesmen and dealers catalogs. Re-printed advertisements touted the R1900 and other plastic marvels in educational publications and teachers periodicals.

Some few schools bought them, and the microscopes for want of educational use found their ways into homes and little hands. It’s telling that rather than being newly broken ground, the R1900 was an off-shoot of an earlier design called simply the 100x. The 60’s were as much the day’s of advertising as the 50’s and where the 100x had difficulty, a change in the color of the plastic resin and expansion of the line (not to mention a noticeable improvement in the optical quality) was only natural if sales were lax.

The robustness of B&L in those days meant it would continue to throw good money after bad for a few more years before the R1900 and it’s ilk disappeared from the market-place to make way for new efforts—the Academic line. Still the R1900 has a place in the companies history and those examples that are out there tend to be in pristine condition and quite usable. There’s little need to keep it as such, as a shelf queen it’s unlikely to appreciate in value so if one comes up at a yard sale or second hand shop don’t hesitate. Give it to a child and them run wild, for goodness sake just don’t buy them a Fisher-Price!

Manuals and printed inserts from the R1900 are now available in the B&L Library.

The Model R1900: part 1

Back in the early 1930’s during “The Great Depression” Bausch & Lomb brought a very capable child-sized microscope called the Model R to market. A few posts about the Model R begin here. The original Model R had a short production run that was interrupted by World War II. When production of the Model R was suspended during the war in favor of such military essentials as binoculars, bombsights, and sunglasses it would never resume. Things were far from over as far as diminutive microscopes called “R” were concerned however, and decades later B&L came out with the model R1900*.

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The B&L Model R and R1900

In many ways the R1900 was the successor of the earlier microscope in name only. While the original Model R strayed only a little from the look and action of full-sized stands, the R1900 took a far different route. The most significant departure is in the operation of the microscope itself. Where once one turned a dial that acted in every way like a simplified focusing knob (coarse focus only) the R1900 offered a rotating body that moved the optics vertically with a horizontal twist of the optical tube.

Gone as well were many of the versatile conveniences of the old Model R. There was no longer a means of setting the body horizontally as one may wish to when observing algae on the vertical side of an aquarium or shear surface of a cliff face. Gone as well is any means of varying the magnification of the microscope.

What it does have are fine optics, a quite intuitive operation, and simple robust contraction required by any microscope intended for the young (or cavalier adult). Additional features of the R1900 not seen in the Model R include a white obverse surface on the substage mirror, and the ability to be easily operated by either right of left hand—this last doubtless an economically motivated choose of the Model R.

Where the earlier Model R was put out into a world where a microscope might have never featured in the average students education, the age of the R1900 was decidedly different. A few short decades meant that a student could almost certainly expect to see the microscope at school or even at home. It further meant that the generation who would be teaches would have had teachers of their own who had benefited from a world flush with optical companies. The Model R was very much an amateurs microscope and the R1900 was to an even greater extent the microscope of a young student. Limited as it was in it’s utility it well overcame the more significant hurdle, of access.

*Also in the product family:

  • The R8900, Recommended for children over 10 years old and for children who have had previous experience with the microscope.
  • The SSM15, Stereo Microscope for three dimensional viewing of rocks, crystals, marine life, insects, plants, etc.
  • The STZ100, Zoomscope with continuously variable magnification from 25 X through 100 X.
  • The STZ200, Zoomscope with continuously variable magnification from 50 X through 200 X.

Prism Projection

I’ve written a bit about the DynaZoom and DynOptic before, I’m almost sure I have, but today I thought a bit about where the stand really shines; teaching.

DynaZoom & DynOptic in the Classroom

The stands of the Dyn* generation aren’t my favorite, the fixed inclination is just something I never understood, even in the BalPlan it’s irksome. There is, however, one thing to which the Dyn* line is particularly well suited and that’s instruction. Simpler U or bird-foot stands have a tendency to be roughly handled by students, and particularly in the case when used with a mirror in the light-path will almost certainly never been in alignment, not so with any of the Dyn*’s. The heavy base sits still and because the illumination is integral (unless used with the rather rare-mirror base) will remain aligned provided it is properly set up once.

They’re also great in that of the various optical heads, the photomicrographic tribute-nocular is enormously common. Although it was available with any number of camera bodies, 4×5, Type 80 Land Camera, Polaroid pack film, even now 35mm remains the most often seen. The comparatively (these days) outdated film cameras provide an excellent jumping off point for someone wishing to adapt a digital camera to the microscope. One could still stumble upon the somewhat rare B&L C-Mount video camera tube and teach a class with a single microscope if one had a mind to. But the right angle prism eye-piece is more common, and can be applied to other stands as well.

The Prism Eyepiece

B&L, perhaps more than any other microscope manufacturer had accessories. There was seemingly a device for every need to be had and at least here, outside of Rochester, New York, many of them still turn up on the yard-sale and thrift-store circuit. The B&L prism eyepiece is one many a microscopist would do well to pick up.

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B&L right angle prism eyepiece

It’s a simple two-part thing, black enamel body bearing a right angle prism in an adjustable mount (the angle of movement is only 10 degrees or so), and a friction fit collar for the eyepiece tube. The collar pulls out from the body and slides easily over most standard 1/16th wall eyepiece tubes where a tiny knurled set screw secures it to the tube. With that in place an eyepiece is installed as normal and the body of the prism eyepiece slipped onto the collar over that. Anyone with more than the most limited experience with B&L illuminators will have noticed that most light sources they made provided a range of illumination that may be described on a scale of too-bright to I’m suddenly blind.

Obviously most illuminators they made we’re meant to be used with skylight or neutral density filters even on their lowest power for visual work. With the prism eyepiece it will be clear just why they provided such ample light.

Demonstration

There’s a lot to be said for the utility of gazing up from the eyepieces for a large and clear view projected upon a wall or screen. Even excluding pains in the neck, it can be Wonderfull for taking notes, or even simply for giving the eyes a bit of a rest, the projection set up for some distance can be a nice way to exercise the focus of ones eyes while not interrupting the use of the microscope.

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Distance to wall, some 27 inches