Before I continue, a very short explanation about luminiscence and fluorescence may be useful.
Photoluminiscence is defined as emission of light not created by an object with a high temperature. (like the sun or a lightbulb). The principle of fluorescence is that (molecules of) the object "absorbs light at wavelengths within its absorption band, and then nearly instantaneously emits light at longer wavelengths within its emission band." In practice the specific wavelength of the mercury arc lamp light will be directed through an excitation filter and a "dichroic beamsplitter".
This light will then be absorbed by the object followed by emission of light with a longer wavelength. This light will pass the emission or barrier filter, which will cut off all light produced at other undesired bandwiths.
In many classic (pre-led) setups for fluorescence microscopy the mercury arc lamp cooperates with a so called "filter block", which is a combination of above menitioned exciter, beamsplitter and barrier filter. Manufacturers of microscopes have created a range of filter blocks, each tailor made for a specific combination of those 3 components.
Are you still reading this article? Good. Now back to the Lumam.
The microscope was manufactured in the USSR 35 years ago, one of its most striking features was the gigantic lamp house that accommodated a 250 Watt high pressure mercury arc HBO lamp.
Now Soviet made technology has the reputation of being overdimensioned and the Lumam R1 is no exception. Mercury arc lamps do require a very specific DC power supply, "in order to provide an up to 50 kiloVolts starting pulse". For this lamp, the designed power supply itself weighed over 30 kg, with an Ampere meter that went up to 10A. I am not sure whether the unit was fused at all, however when starting it up it made a frightening loud humming noise, which remained throughout the session. Meantime the power cable got seriously hot and after a session I found it discoloured as well. To make a long story short: I had to say goodbye to both the lamp (with its nice asbestos gaskets and slightly corroded connections) as well as its power supply.
When I started posting on this forum 3 years ago I've been using the instrument without that feature, experimenting e.g. with feeding white led light through the epi-objectives. Mmmm. So the plan was to restore the fluorescence functionality. On one hand as an alternative high power leds turned out to be very popular. But how would they cooperate with the filter cubes and would the intensity and distribution of led light be comparable with what came from the original mercury arc lamp? Therefore I wanted to stick to the original design as much as possible, and continue using a HBO lamp. Now 250 Watt mercury arc lamps are rather extravagant and affordable combinations of complete lamphouses with operational power supplies are rare (read: impossible to find). Finally I decided to give it a go with the popular 100 Watt variant, and that's where this project started.
A Nikon Optiphot 100 Watt lamphouse and power supply were found for a reasonable price and installed in position of the original lamp house, utilizing a part of it (see below pictures).
As the unit had its own collector lens, the original russian collector lens had to be removed. Its weight: over half a kilogram! The next item in the light path was what looks a bit like a small fish tank designed to whitstand serious static pressures: this was the heat filter that had to be filled with water and copper sulphate in order to protect the rest of the optical path against oven-level temperatures. I removed that one too. (though considering to reinstall some other kind of heat filter)
Important within the whole setup are the epi objectives. Initially, the 9x and 21x magnification objectives were part of the set, later it was easy to find the 40x and 95x lenses via Ebay. They're all M27 thread, which is wider than the standard RMS that can be found on most microscopes. Parfocality was another issue. The objectives, obviously designed within the same range somehow turned out to have different distances from the object. I've discussed this issue with a well known Lomo reseller in Russia a couple of years ago, and he was kind enough to find a solution and based on his technical library, started producing extension pieces with the correct length.
https://www.ebay.com/itm/Set-of-4-exten ... SwY3BZFMDt
The original set had three filter blocks as well, labeled green, blue and red, each with its own combination of dichrioc mirror/barrier filter. (A fourth one was "empty", to be used for reflected darkfield observation).
Furthermore a range of 16 excitation filters was supplied, covering several specific bandwiths. As the mercury arc lamp cannot be dimmed, in order to reduce the light intensity, identical filters can be placed in series in the designated slot. That is the reason why Lomo exciter filter sets often have double -or even more- identical exciter filters. The Lumam can handle three filters at the same time, see below picture.
After starting up the unit (the hour counter of the power supply had been reset by the previous owner), the mercury arc lamp had to be adjusted, in order to create a good image of the light source.
As the original collector lens had been removed and the image of a 250 Watt mercury arc is likely to be larger than its 100W equivalent, this image turned out to be smaller than hoped for. In order to rectify this, one of the lenses of the original collector (it was made of 4 different lenses, which explains the weight) was found suitable to relay the Nikon collector lens, installed between the exciter slots and the new lamphouse. (also in above picture)
As I had to learn more about this instrument, googling make and type name, also in cyrillic turned out to be useful: a 13 page instruction manual for the Lumam range...in russian..., was found. (http://neoton.su/d/312290/d/-data-docum ... 8_lomo.pdf) In order to improve my russian, I started reading it and discovered the specific recommendations made by Lomo for combinations of exciter filters with filter/mirror blocks. (as mentioned, contrary to other makers configurations, the exciter filters are completely separate from the filter block units.) When crosschecking these recommended combinations, most of mentioned filters where not part of those 16. Fortunately a seller in Russia was discovered who could provide that "missing link" for a reasonable price. Expect to receive these soon.
So basically that's the half time score of this project. With a bit of trial and error various filter combinations were tested and I feel the results are encouraging. The blue filter block is providing interesting results with one specific exciter, resulting in red for chlorophyl and white for cellulose in plant material, the green filter is useful for pollen, see below test pictures. Unfortunately it is hard to conclude how many hours of life are left in the HBO lamp. Fortunately a sealed replacement bulb was found for a fraction of the normal price, would like to wait a while with replacing it and first assess the performance of the current bulb.
To be continued...
11> Geranium leaf, detail 9x/0,20
12>Moss, ditto
These are also part of above mentioned set as well as the initial set. (same picture, lower row)
