Notes on some lighting options
compiled by David Walker, UK
LOMO Biolam* microscopes are frequently auctioned on eBay (UK) and can be excellent value. The commonest stands sold have a mirror so the buyer will require a light source. This article summarises a selection of lighting options hopefully of use to the Biolam purchaser who is unclear of what is available. Both homemade lamps and most in the LOMO range are covered with comments on their relative merits and tips on using them. (*The variants of the Biolam stand inscribed 'P1Y4.2' shown above is being referred to here.)
The comments are based on the author's lamp examples dated ca. 1970-80s and are those likely to be sold used in the UK. I'm not certain if the Biolam microscopes and lamps in countries where offered new are of the same design or what bulbs are currently supplied. Some modern Biolam type stands do now come with built in lighting.
If unfamiliar with the types of microscope lighting e.g. 'Kohler' and 'critical', Frithjof Sterrenburg's Microscopy Primer gives an overview.
Comments to the compiler David Walker are welcomed.
page isn't intended to be read linearly; lamps are admittedly unexciting but vital,
so just dip in to any option of interest!
All images by the compiler unless otherwise indicated.
Getting started lamps / homemade
Getting started lighting:
Desk lamp with photoenlarger bulb. Simple but gives good lighting and one of the best for lowest mag.
Image courtesy Ian Walker.
Others: Homemade fibre optics. A neat and effective design for the LOMO with photo capability by Ted Clarke.
Image courtesy Ted Clarke.
A simple dual tungsten flash lighting set-up for photomicrography using the OI-19.
Tips to improve OI-19 and OI-35. Changing out supplied Russian bulb and comments on diffuser use.
HLS-1 quartz halogen base. A professional and neat bolt on design.
Images T&OE leaflet, ca. 1970's.
All the external lamps discussed are best used with
the flat side of the mirror.
Tip: If a lamp is poor at the lowest mag, take out the condenser and try using just with the mirror and the lamp.
A wide variety of other lamps have been shared by Micscape contributors. See the Micscape Library - Techniques - Lighting section.
Getting started lighting.
Slide box for viewing 35mm photo slides.
(The microscope is on a variable height computer monitor stand; a good way of raising its height to a comfortable viewing height and creates dust free storage space underneath. See this topical tip.)
Daylight: This is such an unreliable light source (especially in the UK!) and rules out any after dark microscopy that it's not really a viable option for regular use. Also need to be careful, especially with kids, that the mirror doesn't pick up a direct image of the sun. Directing the mirror at a north facing window indoors is OK or if in the field where light source options may be limited.
Light box for 35mm photo slides: I recently bought a small fluorescent light box (5x4 inch lit area) for ten pounds or so for it's real use but it's also an excellent glare free, white light source. It's the only light source I know of that can evenly fill the field of view with a 3.5x objective with no bulls eye or diffuser. It's best to buy with the maker's recommended power supply (a small plug-in wall adaptor) as the batteries don't last long.
It's not an intense light source but fine for
low to mid power brightfield visual observations and a useful readily available stepping stone for better lighting.
This is a good lamp for the kids to use because
it's cold running with external low voltage* supply,
so if pond water is being splashed about,
* Higher voltages are generated inside the unit to drive the fluorescent tube so must not be dismantled to change bulb when live.
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Desk lamp fitted with photoenlarger bulb.
A well ventilated and earthed ca. 60W desk lamp such as the design shown can make the basis of a good microscope lamp to start out with at little cost. Domestic light bulbs aren't very evenly frosted but can be changed out for an equivalent wattage photoenlarger bulb available for a few pounds from camera shops. These give a much whiter light and very even frosting without much glare. Although a very simple modification and lamp design, this in the author's opinion is capable of giving excellent illumination and superior in some respects to the less than perfect LOMO Kohler lamps. It's particularly useful at the lowest mags because of its large illuminated area as no extra diffusers are needed in the light path and where even lighting with Kohler can be tricky.
I've used one successfully for many years for quite a lot of visual work and photography at low to mid microscope powers but does start to be underpowered for techniques such as darkfield and polar filter uses. It's quite bright as diffusers aren't needed and works well with the Abbe condenser bulls-eye for the lowest 3.5x objective.
The lamp is used in a variant of the so-called critical illumination mode, which sounds techie but simply means that with subject focussed on slide the condenser is focussed on the lamp frosting, although it's a benefit to slightly defocus to remove any hint of frosting structure. It doesn't have a field iris but the bulb is relatively glare free, (point lamp down as shown so as the bulb is not seen at eye level to minimise glare).
Safety notes: Don't be tempted to change out the maker's recommended wattage bulb in the desk lamp for a higher wattage photoenlarger bulb as this is unsafe, potentially causing overheating and even fire. Desk lamps like these do get hot in normal use so best not to use unattended or where kids can touch them. Also if studying aquatic samples, handling water around the microscope and near a mains operated lamp isn't ideal even if correctly earthed, so low voltage lamps are a safer long term solution.
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High intensity OI-19 lamp
OI-19 lamp; also shown with a simple but effective set-up for quickly
switching to flash for photomicrography.
Uses a 8V/20W tungsten bulb with Ba 15d base powered by a variable low voltage power supply.
Focussing by the friction fit lamp base, with two element field lens and field diaphragm. No lamp centering but the bulbs are usually reasonably centred.
Has the important features required for Kohler.
Versatile. It rapidly doubles up as a lamp for top lighting simply by raising the lamp holder on the stand.
The design allows simple electronic flash to be available quickly, see this article for an example.
Mechanically sturdy and hard wearing paint finish.
Limitations: Uneven lighting if used without diffusers. Poor light coverage at lowest mags. 20W isn't sufficient for some microscopy techniques with photography especially if diffusers used, e.g. darkfield and phase at higher powers. (Note that some 'limitations' aren't unique to this lamp but a limitation of 'Kohler' type lamp designs with small bulb filaments; see comments in Tips to improve.)
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Kohler OI-35 lamp (these notes apply to the older lamp likely to be sourced secondhand).
Iris and condenser focus on tube. Internal mirror adjustable by silver
screws for filament alignment. Bulb centrable at back of bulb housing.
Shares the same features as OI-19 with addition of centering lamp housing.
Lamp fits in the hole in the Biolam stand base with the mirror removed.
All the features required for Kohler.
The design avoids alignment errors with external lighting.
Offers no significantly better quality lighting than OI-19 and similar disadvantages in light unevenness without a diffuser and intensity loss with diffusers.
The unit is deep and gives a congested understage preventing dual tungsten / flash set up possible for the OI-19. Also less convenient for quick condenser changes.
(Note that some 'limitations' aren't unique to this lamp but a limitation of 'Kohler' type lamp designs with small bulb filaments; see comments in Tips to improve.)
After stripping down the OI-35 lamp and comparing with the OI-19, the former seems to use the same field lens. So if used with the Russian bulbs supplied in the 1970's/80's and which may come with a secondhand sourced lamp, the Kohler is not even enough for photomicroscopy unless a diffuser used. I bought my OI-35 for £39 at a club meet and can be good value secondhand. The new OI-35 variant at typically $590 seems to be externally similar but note it is advertised with a 6V/15W halogen bulb so the bulb may be an improvement on the tungsten. The high price new of this lamp isn't unique to LOMO, although Kohler lamps are optically and mechanically much simpler than a microscope, they are often sold for much more than the cost of the microscope. Update Nov. 16th: Just found a US dealer selling an OI-35 variant for $125 with an 8V/50W bulb so the price and spec seems to vary quite widely.
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Tips to improve the OI-19 and OI-35 lamps.
1) Change the bulb for a better one if needed.
A fellow LOMO enthusiast suggested to me some years ago to change the Russian supplied (8V / 20W) bulb in the LOMO for a Philips 13347W (6V / 15W), so pass this tip on. To ensure the bulb isn't overrun, a marker can be put on the intensity knob dial at 6V. It's worth checking with a voltmeter when the bulb is under load what the exact setting for 6V is, as the graduations on the power supply aren't always accurate.
2) Use of diffusers supplied
The limitations of achieving even Kohler lighting with a small filament bulb, field lens and no diffuser especially at lower powers isn't unique to the LOMO lamps. The big name microscope makers' built-in lighting often has a permanent or removable diffuser in the light train, with or without an option on the condenser for low power objectives. The microscopy text books often note that the only place a diffuser can be inserted to retain Kohler is in front of bulb but before the condenser and many makers adopt this.
LOMO do supply a range of diffusing plates for the LOMO lamps but not practical to adopt the recommended diffuser positioning. For practicality and for non-critical work, putting the diffuser in the condenser filter tray with or without the swing in bulls-eye on Russian Abbe condenser is fine. I've read that some hobbyists sand the front of the bulb to give a diffuser but my attempts were disappointing and lose the option to use a clear bulb at higher powers when desired.
The problem with diffusers either permanently built-in or optionally added is that they cause a large drop in light intensity and the 15-20W lamps typically used in many microscopes can run out of steam at higher powers or for techniques like darkfield, phase or polar filter use. It's best to experiment with or without diffusers with a given objective and subject to see if the image quality is being deteriorated; some loss of perfectly even field for visual or photo work may be preferable to loss of quality. Paul James gives a good overview of the pros and cons of diffuser use in this article, Illumination variants, diffuse lighting.
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HLS-1 quartz halogen lamp base
Left: HLS-1 on LOMO. The two screws on base centre the bulb.
Right: lamp base detail and typical power supply. The bulb is centred using spring tensioned screws acting on the ceramic bulb base.
The removed field lens in sturdy metal mount is also shown.
A sturdy cast metal base for the Biolam stand with centrable 6V/20W (G4 fitting) quartz halogen lamp and variable intensity power supply. A single element field lens sits in the hole on LOMO base with mirror removed.
This is probably the most professional and neatest looking lighting option for the LOMO, effectively converting it to an internal lighting stand with the benefit that has on alignment and space saving.
Also quartz halogen gives a whiter light.
The bottom face of the field lens is ground glass so it's a permanent diffuser to give good even lighting. The lamp base screws to the underside of the Biolam and gives a noticeably more rigid unit and also provides a useful height increase as the LOMO stand sits rather low on a typical desk. Some LOMO's come up on eBay with this lamp fitted and sometimes with the larger fitted wooden box to accomodate it.
The diffuser does significantly drop the potential light output from the lamp, nullifying to some extent the benefit of quartz halogen cf tungsten. From the author's tests, it's not significantly brighter than the OI-19 and OI-35 where there's the option to use without a diffuser.
As an experiment the author painted the ground glass surface with clear nail varnish which almost makes it a clear element so then offers the option of using the Abbe condenser bulls-eye and/or diffuser depending on light intensity required. This is reversible by cleaning element with acetone. The author preferred ground glass on element overall.
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LOMO 'substage lamps' and thirty party models
Left: LOMO OI-32E. Right: LOMO SL-4.
The author has no experience of these lamps, but from TOE's (a former UK distributor) 1970's spec. sheets (from which images right are sourced) they use mains voltage 15W bulbs. A used microscope may come with one of these.
The SL-4 replaces the mirror with prong shown and is a simple design with frosted glass. Third party designs for microscopes with a mirror are also available from dealers but one of the other designs is better for regular use.
The OI-32E sits in the hole in the stand base after removing the mirror and a more stable design than the SL-4. It is described as having a condenser and has a filter tray so should be more competent than the above. Homemade field stops can be made for this if desired. See this Micscape Topical Tip by Ian Walker.
The intensity of such lamps are fixed and lack a field stop so can suffer from too much or too little light intensity depending on mag used. Neutral density filters or polaroid filter can reduce intensity if there's glare at lower mags.
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Published in the October 2005 edition of Micscape.
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