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).


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


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.

10-16-2018 1 copy

Birdhouse on 127 size Kodak BW400CN



Amateur Photomicrography II


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.


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*.


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.


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.


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.


Distance to wall, some 27 inches

Light Source Power Supply Alternatives

Get an amazing deal on a stand and have everything you need except the power supply? Don’t leave it on the shelf in the hope of one day converting it for an alternative bulb (LED conversion can be great, it can also be terrible, don’t rush into it) or wait for the day to come when an appropriate transformer turns up, just buy an autotransformer! A suitable autotransformer won’t exactly be cheap but can prove quite economical in the long run, we’ll get to that later, first lets look at what one is, and what’s normally provided. First a little bit about power, lights, and dimmers.

Most of the time, in a residential application that is, light bulbs provide a constant fixed level of brightness (marked on packages in lumens) but generally thought of by the consumer in terms of watts. A watt is a description of energy that is equal to the voltage multiplied by the amperage. The conventional 60w incandescent light bulb may be powered by 120v at half an amp of current, or 12v at 5a. Years ago if one wanted to get a lower level of illumination from an incandescent bulb one used a dimmer switch that contained a variable resistor that limited the voltage which traveled to the bulb the current remained the same. We can see then that the same bulb which provided 60w of illumination at 120v and half an amp would provide 30w at 60v and half an amp. With these type of dimmers the energy that is restricted by the dimmer (30w) is dissipated by the dimmer as heat, no energy is saved, between the dimmer (30w) and the bulb (30w) one is still using 120v and half an amp.

More modern dimmers operate by means of a simple circuit that rapidly turns power traveling to the bulb on and off. It happens so fast that it’s invisible to the eye and with incandescent bulbs the heat held by the filament makes the fluctuation even less noticeable. The advantage of such a dimmer is that there is some minor reduction in power consumption—the reduced wattage output by the bulb is not dissipated by the dimmer as heat. Unfortunately, a by product of such a dimmer is a reduction in the working life of the bulb which should avoided like the plague in the case of frequently difficult to find and expensive to replace microscope illuminator bulbs. Both of these dimmer types, both the old fashioned and modern have one significant flaw for the microscopist—in a word current—but more on that later.

An autotransformer is and electrical voltage transformer of a special sort, functionally a dimmer of the old-fashioned type described above, yet instead of functioning like a resistor it’s a transformer and functions due to induction. Unlike a standard transformer with a primary winding of a particular number of turns and at least one secondary winding of a differing number of turns, an auto transformer has only one winding. In a normal transformer the supply voltage is connected to the primary winding and is output at the secondary at a different voltage that can be calculated with a set of equations.

If the primary has more turns of wire than the secondary the input voltage produces a lower voltage on the secondary it’s called a step down transformer. If the situation is reversed and the primary has fewer turns than the secondary (or the secondary from the first example is used as the primary) it’s a step up transformer and outputs a higher voltage than was input. This is how the old, heavy, wall adapters are able to output 12v even though the socket on the wall provides 120v or 240v.

An autotransformer isn’t automated or automatic, rather it’s so designated for the fact that it is self-transforming. In place of two separate windings a single continuous winding is used for both the primary and secondary. The use of a single winding means an autotransformer rated for a particular input and output voltage will be much smaller than a standard transformer with a primary and a secondary. With most autotransformers the primary and secondary are not in a fixed permanent relationship, but are variable across a given number of steps.  One might just as easily be continuously variable across a range. Most are able to provide an output from significantly lower than the input voltage to a bit over, though others are constructed specifically to provide much higher output voltages than those input. For the purposes here we’ll want an autotransformer which takes a standard input voltage and can output a range from < 1 up to > the input voltage. The practical application of such a device is that an significant number of different bulbs can be run from a single transformer rather than needing a different unit for any particular microscope.

At most hardware stores a standard lamp dimmer can be had for as little as ten dollars, throw in a box in which to mount it and a hardwood base and the whole deal still only just approaches twenty bucks. A secondhand autotransformer might turn up for $50 but one is better off buying new where one can find a 120v autotransformer rated for 20a (of the cheapest sort mind you) for around a hundred, more than five times the cost of a dimmer switch. An autotransformer as described above even if rated for only 10a might weigh as much as twenty or thirty pounds. The reason an autotransformer is preferable has to do with amps and volts. A dimmer switch will only work at the rated voltage, but that’s still not the worst thing about them, after all many student microscopes from the 1960’s and even the 1980’s used a 15w 120v night-light style bulb, it’s a question of current.

The dimmers at the local hardware will at most be rated for 4a, maybe a few for high voltage halogen track lights go as high as 5 or 6a. That’s more than enough for a single incandescent drawing even 2 to 3a at the most. Now, something like the B&L Dynoptic that takes a GE-1634 only draws a single amp, a touch more if over-run to 25v, so a small resistive dimmer would do if installed after a step-down transformer, but it wouldn’t be very efficient. That same bulb could be easily be run by an autotransformer, place a tape mark or two on the control knob to a avoid accidentally feeding it a drastic over voltage and you’re in business.

Where the autotransformer really stands out however, is when it comes to running much older lamps from much different types of illuminators. The first incarnation of the B&L Research Illuminator dates to the early days of electricity and took a range of bulbs from 120vAC to battery based 24vDC home electrification systems that were in use in rural areas for decades before rural electrification ramped up the late 1930’s and post war 1940’s. The second and re-designed Research Illuminator (the model with the rectangular horseshoe base) took as standard a flat filament incandescent that was rated for 18a at 6v. The original power supply for the 100w bulb was about the size of a breadbox and looked and acted much like an early electric space-heater.

The all-metal units contained a large step-down transformer and a multi position switch that would remove one large resistor from series for each step the switch was moved to increase voltage fed to the lamp. It might seem strange that the unit simply didn’t employ a number of secondary windings and so provide a range of voltages with a single component. The use of the resistors made the unit smaller and cheaper to manufacture. Some workers would strip the switched resistor series and replace it with a rheostat (a large type of continuously variable resistor still manufactured but not now in common use) thereby obtaining a continuously variable voltage. In practice the unit was not so different from the device used to run electrical arc illuminators, but had the added benefit of using lower voltage at the output (and using a bulb rather than a cumbersome carbon rod gap).

Using an autotransformer with a B&L Research Illuminator means I don’t have to spring for a supply that runs into the hundreds of dollars even when it does turn up for sale. It additionally means not having to worry about setting fire to the workbench, antique electrical apparatus isn’t known for its safety. Furthermore, autotransformers are always constructed with a fuse, which means that in place of the standard 20a slow-blow fuse (as a rule fuse amperage is identical to the rated current) I can use a fast-blow fuse rated for the amps drawn by the lamp being employed, and add a further level of protection for my bulbs filament.

Beyond that there’s the convince factor. The autotransformer is able to supply the required power for every illuminator I have, everything from the 120v Optilume, to the 115v lamp in the Spherical Illuminator, or down to the 6v halogen in the BalPlan. Even the high intensity 6v 18a (think about that, 18a, the breakers in your utility room are probably only rated for 15a on a lighting circuit!) bulb in the the Research Illuminator. So should we throw out the power supplies we do have in favor of an autotransformer? Of course not, but we should be mindful of it as a safe an effective option for feeding power to a microscope lamp of a variety of illumination systems.

Next time something with pictures, I promise. -K

Light Source Power Supply Anomalies

I’ve been meaning to write about power supplies for some time and a recent exchange reminded me of one of the reasons I was initially prompted to. Anyone who’s frequented this odd little website is aware of my feelings concerning used microscopes; in the words of a breakfast cereal mascot “they’re great!” One thing that is perhaps not so great, completeness. By this I of course refer to the tendency of second hand stands to be somewhat incomplete, particularly as regards light sources and power supplies.

Now the absence of a lamp housing and mount should, as a rule, be considered a deal breaker for a stand that requires one. Very rarely, one might find and recognize a needed lamp housing but the search is liable to be complicated by sellers who are uninformed and so list the item under difficult terms or worse by informed sellers who know the proper terms and therefore the rarity and value of the item. This isn’t about lamp housings though, this is about another component that if missing does not disqualify an otherwise complete or desirable stand from consideration; I write of course of the lamps power supply.

Another enthusiast contacted me with a question about a B&L transformer. As I looked through the manuals for a part number I noticed something interesting. Two versions of the manual for the Dynoptic & DynaZoom had two different sets of published voltages! One version of the manual described the five taps as having the first set of voltages, the other the second. Oddly enough each manual recommended the same GE-1634 lamp.

  1. 1v – 2.2v – 4.5v – 9v -21v
  2. 12v – 14v – 16.5v – 20v – 25v

Admittedly, that’s a 20v bulb, so it’s entirely possible that two version of the transformer were made. Somewhat more unusual is the lack of a specific part number listed in either manual for the transformer itself. B&L at one time or another assigned part numbers to everything from screws to shims, so I’m a little concerned that I only failed in my search because I didn’t read as carefully as I might have. I took a multimeter to each of the corresponding transformers in my collection and both proved to me of the higher voltage varieties. It’s not at all uncommon for a microscope illuminator to provide higher voltage than that for which the bulb is rated. In older textbooks and even on some modern transformers the final tap, or range on continuously variable transformers, is marked as “OV” for over voltage generally called over run. The fact that the second set is so much higher than the first would tend to disqualify the first transformer for photomicrographic work. I’d go so far as to say the binocular heads should not used with the first transformer if one intends to use a daylight filter, and the second shouldn’t be used for visual work without one, or at least a set of neutral density filters.

What I’d like to point out, is not that the published voltages of a transformer may not line up with a transformer that “looks like” the one in hand, or that is available for purchase. Rather, that the important thing is the supply provided by the transformer and its suitability not only for the bulb employed but also the intended use. It’s a simple thing really, and something that might be forgiven for someone who’s only had to deal with common lightbulbs of the sort had at the average home store or hardware. Where then should the enterprising microscopist begin in outfitting a microscopes illumination system? With the correct bulb. The correct bulb will be mechanically compatible with the bulb holder and lamp house as well as of the rated wattage.

I write of wattage because at the beginning the most important and most frequently overlooked characteristic of a bulb is the heat which it will put out. Over high wattages will present a fire hazard, apart from the potential damage to a stand one might also damage the eyes, so do consider the wattage when choosing a replacement bulb. If at all possible always use the bulb recommended by the manufacturer, or a mechanically compatible bulb of lower wattage.

And this weekend, the part I’ve been meaning to write! -K