Geologists like me teach students and conduct research with microscopes called "polarizing" or "pol" for short. After development in the late 19th century, pol scopes became critical tools for identifying the minerals and structures of rocks (our Earth), and for determining much about how they formed. Such users are petrologists, who are doing petrography. This type of microscope is also used by mineralogists, geophysicists, soil scientists, crystal chemists, materials engineers, medical researchers, asbestos consultants, and many others including biologists. The method that can be employed with these instruments is called PLM (polarized light microscopy). "Simple polarizing" scopes are usually just biological microscopes with pol filters, one inserted under the head and another in a substage filter holder. Any scope can be so modified, including stereo microscopes (but the common style is a compound microscope). Those designed for geological work are also known as "petrographic" (="rock imaging") microscopes, which have accessories to assist mineral studies in rock sections.

Many crystalline materials (organic as well as inorganic) produce interesting optical effects with both polarizers in place, and some biological samples can show useful changes of contrast against a dark background. 

In my research lab, an Olympus BH2 BHSP petrographic polarizing microscope (below) is serving me well, and I am convinced that it is the best of the 20th century "benchtop" pol microscopes. I will use it to illustrate pol scopes.

You might disagree with this assessment, but in my research and business I have used more than two dozen different petrographic microscopes of many brands and models. Actually, I liked them all, but some were better than others in design, function, and quality. Six of the best pol scopes in my experience are the subject of my article in the internet journal called Micscape, also linked below. I have also described some interesting student petrographic microscopes in that journal. More recently, I have added a super-wide head and eyepieces with a view field number of 26.5. It includes about 2.65 mm of slide in the view with the 10x objective, or 6.625 mm with the 4x, which is huge. Very nice for scanning coarse grained rock slides. But I had to renovate stuck diopters on the oculars for it, which I described in this Micscape article.

Another Micscape article describes the path to obtaining my BHSP, including earlier petrographic microscopes that I used for geological research. New 21st century models such as the Zeiss Axioskop Pol or Olympus BX-51P are no doubt even better microscopes than my late 1980s machine, but it will be a long time before such new and very expensive microscopes come into my budget range. In fact, there are a good number of late 20th century microscopes that can meet personal and professional requirements, and also be satisfying to own and use.

How is it different?

There is nothing especially mysterious or strange about the polarized light accessories used in a petrographic microscope. Its brightfield capabilities remain the same as for any good biological microscope, but with extra parts that can be used or not used, as you wish. The polarizing filters are placed above and below the sample, and the upper one can be easily moved in and out of the light path. A circular stage rotates to show how different orientations of the sample affect polarized light, but it can also be fixed in place for other uses. A Bertrand lens (sometimes only a pinhole with a magnifier) is available to observe polarized light patterns on the back of a higher-power objective. A slot allows the insertion of a filter that adds or subtracts portions of wavelengths of light, called a compensator or wave plate. In models designed after the 1970s, the parts for PLM functions are commonly in modular pieces that can be easily added (or removed) on a standard brightfield microscope stand. 

Polarized Light (PLM)

So, what happens to light in a pol scope? We can think of light as moving in linear rays, with photons vibrating in a plane along the ray, like waves on a shaking rope. Different wave lengths within these vibration planes appear as different colors. Raw light is comprised of many wave lengths and vibration orientations, but a polarizing filter squeezes light into a single plane. Essentially the filter allows through the portions of light that can be oriented into its vibration plane, and blocks the light that cannot fit that direction. The second filter (called the analyzer) has its vibration plane oriented perpendicular to the first, and so no light will pass through it. That is, no light if only air, liquid, glass, or other isotropic material is present between the filters. 

Minerals also polarize light, due to the layers or planes of atoms in their crystal structures. Most actually split and polarize light into two different vibration planes (two refractions, or birefringent). So, if you place a birefringent mineral between the two pol filters, the polarized light coming to it from the first filter is converted into one or two new directions of vibration planes, and some of that light can get through the second filter to reach your eye. Only part of the original light makes it all the way, thus the need for a strong light source.

Light slows down as it moves into the mineral, and the two new polarizing vibration planes conduct light at different rates in the mineral. Each light ray also bends (refracts) as it passes in and out of the mineral, with an angle proportional to its change in velocity. Then they accelerate back to the same speed in the air out the other side. However, the light waves of the rays are now out-of-sync because they moved at different velocities within the mineral. When the wave planes are combined into one plane by the second filter, the waves "interfere" with each other, producing new wavelengths with startling new "interference colors." This amazing feature of birefringence (two refractions) is caused by the two mineral light rays. Birefringence and interference colors vary according to the particular crystal structure unique to each mineral, and so we can interpret important crystallographic properties and identify microscopic minerals, and often infer some of their chemical compositions.

Tools such as compensator wave plates can also provide clues to identification, while reference books provide data tables, optical descriptions, and methodology. There are many written for students and professionals, and you should have one or more. If the book is a few years or decades old, not a problem, as the technique has not changed much, and the minerals not at all! My own library is rather dated, actually. Phillips has several chapters on the use of the universal stage, while Kerr has a fine section on mineral characteristics. Ehlers is one of the most comprehensive resources, and petrography/atlas books are great for illustrating what you actually see. These favorites are:  

Optical Mineralogy by Paul Francis Kerr (1977, McGraw Hill)

Optical Mineralogy by Ernest Ehlers (in two volumes, 1987, Blackwell Scientific)

Mineral Optics by Wm. Revell Phillips (1971, Freeman)

Petrography of Igneous and Metamorphic Rocks by A. R. Philpotts (2003, Prentiss Hall)

Atlas of Rock-Forming Minerals in Thin Section by Mackenzie and Guilford (1984, Longman)

Any crystalline material might reveal features of its structure and chemistry via PLM, including wonderful new colors. Not just inorganic rocks and minerals, but also hard parts of plants and animals, and organic crystals formed by diseases. Interesting and beautiful effects might appear as well as new details, so it is worth a look for almost any sample you are studying. And that is easy to do with a pol scope.

A few images from my basalt slides are below, showing interference colors typical of common birefringent minerals. See this Idaho State University page about thin sections of rocks, which since the late 1800s have provided the evidence for much of what we know about the Earth. Where would science be without microscopes?

Although all the major makers produce models of polarizing microscopes (see below), there has been some decline during recent years in their use in geological education and research. Considering that the Earth is made of rocks, and rocks cannot be studied or understood without petrographic microscopes, this is not good! See this article by Mickey Gunter about the problem.  

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Greg's Leitz Microscopes Page

Here is a separate page about Leitz Wetzlar microscopes, including photos, parts, accessories, documents, and links. All types, not just pol scopes. Other brands (including Leica) will stay on this page for now. These are files that I have collected or borrowed and saw a need to organize. There is not much before the large models of the 1960s and later, so please send me corrections and additions of documents to help the page grow.  Model names, variations, and options for Leitz microscopes are complex and confusing  -- it would be nice if someone (not me) started a Leitz microscopes Yahoo Group or website.

Greg's Olympus Microscopes Page

Here is a separate page about Olympus microscopes, especially the BH2 line, including photos, links, and documents. Biological too, not just pol types. I have a lot of documents and photos of my favorite models from Olympus. This page is mainly about the CH, CH2, BH, and BH2 models, plus some older ones, but I will leave the newer BX and other lines for a future effort.

Several important features common to petrographic microscopes are illustrated in this photo of the middle section of my Olympus BH2 pol scope. Between the head and the arm is an intermediate tube with a Bertrand lens, an analyzer filter, and 6x20 mm slot for a compensating wave plate. The Bertrand lens has a dial to swing it in and out of the light path, with a second dial to focus it. The analyzer (upper polarizing filter) can be moved in and out via a sliding plate, and its part of the tube is marked in degrees for rotation, with a locking screw. Wave plates for the open slot have notches to allow precise stops for an open hole or the wave filter.

The nose turret slides on a dovetail for easy replacement, and holds four DPlan objectives (here 4x, 10x, 20x, 40x) designated PO for their strain-free construction. Three of the turret holes can be centered via side screws, using special small wrenches, or because these are easily lost and hard to replace, small screwdrivers. The same wrenches fit two centering screws for the circular stage, which is graduated in degrees with a lever to engage a "click" every 45 degrees, and a stop screw to lock the stage in place. A special x-y mechanical stage (slide holder) is made with low control knobs, so as to not interfere with the objectives during rotation. It is removable because some petrographers prefer to move slides by hand.

Beneath the stage is a Pol (strain-free) condenser with a flip-up top lens, n.a. 0.25/0.90. This top lens concentrates light for the higher-power objectives, needed when the Bertrand lens is used to make a "conoscopic" view of an "interference figure" (a diagnostic light pattern formed on the the back lens surface of the objective). The lower part of the condenser holds a polarizing filter that can be rotated, with a click for 90-degree "crossed polarizers." On my Olympus, all of these special pieces are very well made, and I take good care of them because they are expensive!

Glass can become slightly polarizing under uneven pressure or if it is not cooled evenly, leaving residual "strain." Because there is usually a pol filter in the light path (under the condenser), an extra source of polarization will add unwanted birefringent effects, so optical parts are constructed (or carefully selected from normal production) to minimize strain. Such objectives, eyepieces, and condensers might be marked P, Po, Pol or SF (strain free), or have red lettering. However, many "regular" optical parts might work OK in your pol scope as well, so it is worth a test. A bigger problem is reflection polarization by mirrors and prisms in binocular and trinocular heads, which is why many older pol scopes use monocular heads. Two-eye viewing is worth some extra cost if you can find a binocular pol head, or if not, you might be willing to put up with slight induced birefringence from a standard biological head. Of course, there will be none if you can swing out or remove both of the pol filters when viewing in "plain" light.

Because they were made in relatively small numbers, or their modular parts could be rather specialized, petrographic microscopes both new and used command premium prices -- often from double to triple the price for a biological version of the same model, depending on how complete it is. If you are outfitting one with additional optical parts, you might find that less expensive objectives, eyepieces, and even condensers from biological (i.e. not certified as strain free) versions work just fine, or at least are so close that their strain effects are hardly noticeable. But if you are buying one at its higher petrographic price, it should already have the proper strain-free versions of optics to get your money's worth (and to preserve its higher resale value).

For several years I counted items with "microscope" in their titles as listed on eBay.com, by brand and type. See eBay Microscopy (an excel spreadsheet) for a table and charts of changes by month in these numbers. A high total near 10,000 items was reached in August 2009, but as the recession eased, the number of microscope listings dropped. Prices dropped too, but have since come back (most are still bargains, but watch out). In 2010, I stopped counting because eBay changed the way it lists items in my microscope categories, and the new counts can not be compared with my record. As you might guess, the big four are the most popular brands, but there are plenty of AO and B&L scopes and parts out there as well. eBay prices for microscopes remain at bargain levels, but there are now a lot more sold at fixed prices, whereas auctions of valuable items at low starting prices are no longer so common.

Also see these notes about adapting Nikon digital cameras to my Olympus BH-2 microscope. On eBay are my Guides to Buying Microscopes and Caring for Microscopes. If you find them to be useful, please check the response boxes so I can stay in the top 1000!

Below are galleries of polarizing microscopes both new and old, some interesting accessories, links to useful websites, and documents including pdf files of scanned instruction manuals. Please consider sharing your pdf documents and jpeg images related to polarizing microscopes (email to me). Thanks to these fine folks for permission to use their images and documents:

American Optical Spencer and Polarstar manual -- William Gasser

AO-Spencer documents on Steve Neeley's website

AO Pol Scopes Catalog -- Humboldt St. Univ. Scientific Instr. Museum

AO Spencer Pol #41 -- Jay Stanley of Classic Optics

B&L Dynoptic Pol scope -- Frank Nasser @ microlites.com

Cooke polarizing microscopes brochure -- Mark Glusker

Gillett & Sibert student scope -- Richard Morris (bluecerise400)

Science-Info website for microscope documents -- Gordon Couger

Swift and Son lab scope, and Wild M21 objectives -- Ray Sloss

Leitz Laborlux and SM Lux Pol scopes -- Ridge Equipment

Leitz Ortholux Pol scope and pol parts -- Tamagno

Leitz Ortholux camera and light meter -- William Day

Leitz Aristomet research scope -- Chip Sanders (mr-keyboard)

Leitz AM Pol and SM Pol scopes -- Raymond Hummelink

Leitz MOP image and 1913 catalog -- Charla Mason

Leitz HM Lux pol scope and brochures -- Allen Carpenter

Leitz older documents -- Don Grybeck

Lomo Min-8 benchtop scope -- Dirk Marel (eapoecistron)

Microscope documents from Gordon Couger's website

Nikon Ske pol scope -- Jay Stanley of Classic Optics

Nikon Alphaphot2 Pol -- John Woodhouse

Nikon Optiphot Pol manual -- Ian Hutcheon

Nikon Microphot Pol image -- petunia_d (eBay seller)

Olympus POM and accessories -- Mike Symons

Olympus AH/BH/CH pol scopes brochure -- Jay Stanley of Classic Optics

Olympus Vanox -- Mark Home (microscopesolutions)

Reichert Zetopan -- electrowise

Unitron brochure -- Jason Weinstein

Zeiss Pol brochures and pricelist -- Paul V. Heinrich

Zeiss Ultraphot II scope -- Frank Nasser @ microlites.com

Zeiss and Leitz price list catalogs -- Jason Weinstein

Zeiss aus Jena benchtop scope -- BIGGERBY2002

About documents and images posted and linked below: Many are scans that I have made from my personal collection of old manuals and brochures, or are my photos of microscopes I have owned. Many others are posted by special  permission but remain the property of the generous donors. Images, documents, and web files might have no copyright notices, but that does NOT mean they are public property, as any corporate lawyer could tell you. Some unscrupulous vendors on eBay use and sell scans without permission, but the ones here are for personal reference only, not for sale or commercial use. If you or your company own rights to any of the files below, and you object to having them posted here, please let me know and I will remove them or their links immediately.  

Documents, files, links, and images on these pages are for your personal use and information, and many are my property or the property of people who have allowed me to post them here. They are not for commercial use including eBay and may not be altered, sold, distributed, or otherwise used without specific permission from me or the people who own them.

Images of Polarizing Microscopes

Models on the Current Market (Spring 2008)

Hinotek polarizing microscopes

JNOEC XPT-7 student scope

JNOEC polarizing microscopes

LEAD Optical PBM-P1 and PBM-P2

Leica DM750P

Leica DM2500P

Leica DM4500P

Lomo microscopes for geology/mineralogy

Meiji polarizing microscopes

Motic BA300Pol

Nikon Eclipse 50i Pol

Nikon Eclipse E200 Pol

Nikon Eclipse E600Pol

Nikon Eclipse LV100 Pol

Ningbo Kingstic PM-002B

Olympus CX-31P

Olympus BX-51P

Unitron Bio-Pol Laboratory

Zeiss Axioskop 40 Pol

Zeiss Axio Scope.A1 

Zeiss Axio Imager

Models Produced in the Past

American Optical Spencer #41 research scope

American Optical Spencer P45 student scope (1960s)

American Optical (Reichert) Series 110 (Polstar)

Bausch&Lomb Dynoptic Polarizing scope model LI (1966)

Bausch&Lomb Dynoptic Polarizing scope model LM (c. 1966)

Cooke, Troughton, & Simms lab scope (1950s)

Gillett & Sibert student scope (1970s)

Leitz Wetzlar Microscopes (separate page link)

Lomo Min-1 field scope

Lomo Min-1 packed in its lunch box

Lomo Min-8 benchtop scope

Meiji ML-Pol lab scope

Meiji ML9200 lab scope

Nikon Ske

Nikon S-Po

Nikon Alphaphot2 Pol

Nikon Labophot Pol

Nikon Optiphot Pol

Nikon Optiphot2 Pol

Nikon Microphot FX Pol (c. 1985)

Olympus POS

Olympus POM

Olympus CHA-P

Olympus BHA-P illustration

Olympus BH2 BHT-P

Olympus BH2 BHS-P

Olympus Vanox AHB (1970s)

PZO stereo scope

PZO stereo scope stages

Reichert Austria Neopan binocular

Reichert Austria small monocular

Reichert Austria benchtop scope

Reichert Zetopan research scope

Selopt Korea student scope

Swift and Son (England) lab scope

Swift-Lomo hybrid lab scope

Unitron MPS (1960s)

Vickers M14/2 monocular lab scope

Vickers M15 monocular w/incident light accessory

Vickers M70 monocular w/incident light accessory

Wild Heerbrugg M21 monocular

Wild Heerbrugg M5 Stereo Photo Viewer

Zeiss aus Jena Laboval 3 student scope

Zeiss aus Jena Amplival benchtop scope

Zeiss GFL (black)

Zeiss Standard 16 binocular (gray)

Zeiss Standard Junior (black)

Zeiss Standard 14 monocular (gray)

Zeiss Standard 16 trinocular (gray)

Zeiss Standard WL Pol

Zeiss Universal Pol

Zeiss Photomicroscope III

Zeiss Ultraphot II (c. 1966)

Parts and Accessories

AO Spencer compensator plates and micrometer slide

AO 110 Polstar stage

CTS incident light attachment w/objectives clip

Leitz Dialux Pol head c.1970

Leitz Dialux Pol condenser c.1970

Lomo Min-8 head tube assembly

McCrone dispersion staining objective

Meiji ML9200 stage

Nikon Coolpix 990 with Leitz Periplan relay lens

Nikon pol objectives (as per Labophot)

Nikon Labophot/Optiphot middle section

Nikon Optiphot2 Pol intermediate tube

Nikon S Pol intermediate tube

Nikon S Pol objectives

Nikon S Pol condenser and turret

Olympus POS objectives and accessories

Olympus POM objectives and accessories

Olympus POM Berek compensator (link to instruction manual)

Olympus CHA-P pol condenser

Olympus BH "simple polarizing" filters

Olympus BHA-P circular stage with mechanical stage

Olympus BH2-SRG circular stage with C-FMP mechanical stage

Olympus BH2-SRP circular stage with A-FMP mechanical stage

Olympus BH2 Berek and wave compensator plates

Olympus BH2 Pol objectives and condenser

Olympus BH2-PA pol intermediate tube

Olympus BH2-KP simple pol intermediate tube

Olympus BHS-LSH 100 watt lamp house

Reichert Neopan-Pol condenser, quartz plate, and lamp

Reichert Neopan-Pol objectives

Reichert Zetopan-Pol analyzer and compensator plates

Unitron MPS centering turret in clutch

Vickers compensating wave plates

Wild M21 pol objectives (centering barrels)

Wild M21 pol stage X-Y slide holder

Zeiss Jena intermediate tube and wave plate

Zeiss black monocular pol head

Zeiss Universal rotary stage w/centering wrench

Zeiss GFL substage

Zeiss Universal Pol middle section

Zeiss pol objectives, 2-ring centering

Zeiss Standard analyzer plate in intermediate tube

Zeiss Standard stage with X-Y slide holder

Zeiss 4x12 mm 1/4 wave (mica) compensator plate

Pol Scope Instruction Manuals and Documents

AO Polarstar Series 2300 reference manual

AO 110 Polstar instruction manual

AO Spenser Polarizing Microscopes catalog, c.1950

AO Blue Book polarizing microscopes chapter, c.1950?

AO 110/120/Series 10 Microstar Analyzer/Polarizer Reference Manual

B&L Dynoptic Polarizing Microscope Instructions, 1966

B&L Polarizing Microscopes catalog, 1970

B&L Polarizing Microscopes price list, July 1970

Cooke polarizing microscopes

Leica Polarization brochure

Leica Polarization Use brochure

Leitz Dialux Pol catalog 55-16a, 1960s

Leitz 1960 Pol Scopes Catalog 55-20 with 1961 price list

Leitz 1971 Pol Scopes Catalog 550

Leitz SM-LUX Pol instructions 550-34

Leitz Orthoplan-Pol instructions (older gray version)

Leitz Orthoplan-Pol brochure (newer white version)

Leitz HM-POL instructions (1970s)

Leitz SM-POL Directions 55-19 (1960s)

Leitz Laborlux-Pol Directions 55-6 (1960s)

Leitz Laborlux Pol instructions (1960s model)

Leitz Laborlux 11 Pol instructions code 933 409 (1980s model)

Leitz Laborlux 12 Pol instructions code 933 407 (1980s model)

Leitz Laborlux 11 S Pol and 12 S Pol brochure (c.1990)

Leitz Dialux Pol Directions 55-12 (early 60s)

Leitz Dialux Pol Instructions 550-12a (late 60s)

Leitz Ortholux -Pol instructions 55-25a

Leitz Ortholux-2 Pol instructions

Leitz Panphot Polarizing Microscope with Photo Equip brochure

Leitz Waldman Hollow Glass Sphere instructions

Leitz Elliptical Compensator Directions

Leitz Berek Compensator Directions

Polarized Light Microscopy (Leitz, 3rd edition, 1985)

Meiji ML-POL instruction manual

Meiji ML-9000 series instruction manual

Nikon Labophot Pol Instructions

Nikon Optiphot Pol instructions

Nikon Optiphot Pol and Labophot Pol Brochure

Nikon Optiphot Pol and Labophot Pol Prices (June 1982)

Olympus POS instruction manual

Olympus POM instruction manual

Olympus AH-Pol instructions

Olympus BH-A-P instruction manual

Olympus AH/BH/CH Pol Scopes Brochure (transitional models)

Olympus BH-2 BHT-P instruction manual

Olympus BH-2 BHS-P instruction manual

Olympus CX31-P brochure

Olympus BHSP-BHTP-CHTP pol scope price list, 1992

Olympus Berek Compensator Instruction Manual (early 70s)

Olympus BX-Pol parts description (1994)

Reichert Neopan-Pol operating instructions (1968)

Spencer 1943 'The Use of Polarizing Microscopes' on Neeley's website

Spencer Polarizing Microscopes catalog with 1948 price list

Unitron Bio-Pol instruction manual

Unitron MPS instructions

Unitron MPS brochure

Wild M21 Polarising Microscope Instructions for Use (larger version)

Wild M21 instruction manual (smaller version)

Zeiss Axioskop 40 Pol brochure

Zeiss Axiolab Pol operating manual

Zeiss polarizing microscopes price list c.1959

Zeiss Winkle polarizing microscopes brochure and parts, c.1959

Zeiss polarizing microscopes brochure c. 2005

Zeiss Standard Pol Operating Instructions

Zeiss Universal Pol Tube Head

Zeiss Universal R Pol brochure

Zeiss Standard Intermediate Tube

Zeiss Standard Pol Accessories

Zeiss Polarizing Microscope Price List (1982)

Zeiss Polarizing Microscopes Catalog (1979)

Zeiss Student Polarizing Microscopes Catalog (1978)

Zeiss Jena Amplival-Pol brochure

Zeiss JenaLab-Pol brochure c.1988

Internet Articles and PLM Websites

Micscape article on "The Six Best Polarizing Microscopes"

Micscape article on "Student Petrographic Microscopes"

Microscopy UK's Micscape Magazine -- see the index for PLM articles

Gordon Couger's website for microscope documents

Molecular Expressions Optical Microscopy Primer

Nikon's MicroscopyU Introduction to Polarized Light

Olympus Polarized Light Microscopy Primer

Olympus Applications of Polarising Microscopy

Olympus Basics of Polarising Microscopy

Microscopy from the Very Beginning

Koehler Illumination Setup

Olympus Polarized Light Image Gallery

Olympus Photomicro Group

How to Buy a Good Microscope

How to Clean Your Microscope

J. M Derochette's Microscopy and Minerals web site

DMOZ directory of microscope dealers and suppliers

Lightscapes Webring for PLM imagery

The Quekett Microscopical Club

Jay Stanley's Wild Heerbrugg M20 site

Microscope Yahoo Tech Group

P. S. Neeley's AO Spenser microscope page

Geology Web Links

Links for Mineralogy and Petrography

Petrography on Answers.com

George's Microscopy Pictures

Making fossil thin sections by hand (Richard Hill)

Making rock thin sections by hand (Greg McHone)

Making thin sections in a geology lab (Union College)

Logitech Thin Section Preparation

Hillquist petrographic machines and supplies

Zeiss Conoscopy and Michel-Lévy Interference Color Chart

Asbestos identification Methodology by PLM - NIOSH 9002

Asbestos Counting Methodology by PCM - NIOSH 7400

More about collecting and analyzing asbestos by PLM

Dispersion Staining article by Walter McCrone

Guide to Thin Section Microscopy (in German)

Geochemical Society issue with universal stage and pol puzzle

My previous Olympus BH2 BHT-P at its "station" and with a Nikon Coolpix 990 digital camera mounted for quick photography. Note the PM-10 automated 35 mm camera controller at right, which is connected to a film camera back that can be easily set in place of the digital camera. The table is a heavy mdf laminate top screwed onto a frame base made of 2x4 lumber, making a rigid and very solid work bench free of tremors.

 

Corporate Websites

Leica

Lomo

Meiji

Motic

Nikon

Olympus

Unitron

Zeiss