DIgital Photomicrography for Gemologists · most significant benefits of the digital age is that pho - tography has become much more cost effective, allow - ing many more people to

144 DIGITAL PHOTOMICROGRAPHY FOR GEMOLOGISTS GEMS & GEMOLOGY SUMMER 2015

The inclusion scenes observed in the micro-world of gems often reveal a tremendousamount about the identity and origin of an un-

known gemstone. By capturing these microcosms ina recorded image, the information is preserved foreasy reference. This information can sometimes belimited due to the photomicrographer’s own knowl-edge of the subject, but resources such as the three-volume Photoatlas of Inclusions in Gemstones(Gübelin and Koivula 1986, 2005, 2008) aid in under-standing the subjects the gemologist may encounterthrough the microscope.

Photomicrography is the method by which im-ages, magnified through a microscope, are collectedby a camera. These images often represent subjectsranging in size from less than 1 mm to 1–2 cm. Pho-tomicrographs do not only serve as educational andresearch references; many are aesthetically pleasingand can be viewed as examples of natural art, andhave even been used as a marketing tool for gem ma-terials (Koivula et al., 1994). All one has to do is at-tach a camera in the optical path of a microscope totake advantage of the beautiful micro-world of gems.This was previously accomplished using film, oftenwith tremendous results due to the superb color ren-dition and high resolution that film could offer. Thedownside to this method is the expense of developing

and the delay in seeing the resultant image. As pre-dicted by Koivula (2003), the limitations of film haveessentially been eliminated by the digital age. Digitalcamera technology has developed to the point thatimage quality rivals that of film, and the photomi-crographer no longer incurs the cost of developingfilm just to see the resultant image. Digital photog-raphy also allows for instantly viewing captured im-ages and in making post-processing adjustments thatgives the photographer the ability to compensate forsub-par lighting conditions and make post-capturecorrections. This article covers the basics of gemo-logical photomicrography, from equipment configu-rations to lighting conditions and image processingsoftware, which will assist aspiring photomicrogra-phers in merging science and art (figure 1).

THE MICROSCOPEThe most practical photomicrography system beginswith a trinocular microscope to allow traditional ob-servation and image capture simultaneously. How-ever, a binocular microscope with a live display to avideo monitor may also provide sufficient results,even if it is not as easy to use. There are many limit-ing factors in photomicrography, one of which is thequality of the optics between the subject and thecamera. For the best results, photomicrographersshould acquire the best optics possible within theirbudget. It is usually better to purchase a used high-quality microscope with excellent optics than a newmicroscope with merely adequate optics. As Internetcommerce has evolved, it has become quite easy to

DIGITAL PHOTOMICROGRAPHY FORGEMOLOGISTSNathan Renfro

FEATURE ARTICLES

Until recently, film was the preferred medium used for capturing images through the microscope, pri-marily due to resolution limitations of digital-format cameras. The image quality that can now beachieved by digital cameras is equal, and in many ways superior, to the quality offered by film. Digitalphotomicrography allows gemologists the opportunity to instantly see the resultant images, which canthen be adjusted with image-refining software so that they represent their subject as realistically as pos-sible. This article offers examples of some basic techniques and tips on the application of digital pro-cessing to get the most out of photomicrographs.

See end of article for About the Authors and Acknowledgments.GEMS & GEMOLOGY, Vol. 51, No. 2, pp. 144–159,http://dx.doi.org/10.5741/GEMS.51.2.144.© 2015 Gemological Institute of America

purchase a high-quality used microscope for a rea-sonable price; however, this cost will still be in therange of a few thousand dollars for a good used mi-croscope in working order. New microscopes withhigh-quality optics will cost several times that. Two

recommended models no longer in production, butoften available from online resellers, are the WildHeerbrugg M400 series photomacroscopes and theNikon SMZ10 trinocular head microscope (figure 2).Both instruments have excellent optics but offer

DIGITAL PHOTOMICROGRAPHY FOR GEMOLOGISTS GEMS & GEMOLOGY SUMMER 2015 145

Figure 1. The blackmanganese oxide“plumes” in this Aus-tralian opal serve as agood example of art andscience merging ingemology. Photomicro-graph by Nathan Ren-fro, field of view 5.85mm. Note: Field of viewis horizontal through-out this paper unlessotherwise specified.

Figure 2. Top left: The au-thor’s photo micrographyequipment consists of aNikon SMZ-10 micro scopewith custom darkfield basemated to a Canon 6DDSLR camera with two bifurcated fiber-optic illu-minators. Bottom left: ThisWild Heerbrugg M450 photomacroscope withApozoom lens is mountedto a Macrorail steppingmast bolted to a Thorlabsoptical table with a Canon5D Mark II camera. Right:The GIA DLScope trinocu-lar microscope is easilyequipped for photomicrog-raphy, as shown with aCanon 70D DSLR camera,bifurcated fiber-optic illu-minator, and auxiliary dou-bling lens. Photos byNathan Renfro (top left),Darren Bates (bottom left),and Ziyin Sun (right).


Gemological microscopy has evolved from the late 19thcentury drawtube brass microscopes (figure 3, top left)into using much more advanced stereomicroscopes thatprimarily used dark field illumination. The applicationof this lighting to gemology was first patented byRobert Shipley Jr. in 1939 (figure 3, top right) (U.S.Patent no. 2,157,437); darkfield has essentially beenthe standard lighting environment for gemology eversince. Though there have been some advancement inoptical trains and ergonomics, the gemological micro-scope has remained largely unchanged for severaldecades. In 2011, GIA’s Carlsbad laboratory acquired acustom-outfitted compound microscope for researchapplications. This Nikon Eclipse LV100 (figure 3, bot-tom left) can provide a viewing magnification of up to1000×, whereas standard gemological microscopes usu-ally have a maximum viewing magnification of ap-proximately 120× with the use of an auxiliary doublinglens. This microscope system is outfitted with extra-

long working distance objectives, differential interfer-ence contrast components, an assortment of filters,fluores cence imaging capabilities, and Nikon’s NIS-El-ements software, which can control the stage heightfor automated extended depth-of-field imaging. Thismicroscope will allow researchers to reexamine speci-mens with a new perspective and could enable the ob-servation of previously unseen features in gemmaterials. While not necessarily a practical microscopefor routine gemological examination, this type of sys-tem could represent the future in gemological discov-ery. In April 2015, the inclusion research departmentat the Carlsbad lab acquired a well-equipped NikonSMZ25 microscope system with a 25:1 zoom ratio, aNikon DS-Ri2 high-resolution digital camera andSuper High Resolution (SHR) objectives (figure 3, bot-tom right). This microscope system demonstrates thelatest developments in optical microscopy and digitalphotomicrography.

BOX A: THE EVOLUTION OF THE GEMOLOGICAL MICROSCOPE

Figure 3. Top left: This late 19th century brassmonocular microscope was outfitted for studyinggemstones, and its base is stamped “The Gemmo-scope.” Top right: This Bausch and Lomb micro-scope uses the Shipley patented darkfield lightingenvironment, which has become the standard ingemology. Bottom left: The author examines thesurface of a diamond crystal using the GIA Carls-bad laboratory’s Nikon Eclipse LV100 compoundmicroscope. Bottom right: GIA’s analytical micro-scopist, John Koivula, with a recently acquiredNikon SMZ25 microscope. Photos by Nathan Ren-fro (top) and Kevin Schumacher (bottom).

their own unique features. The Nikon SMZ10 hasthe ability to capture stereo pairs for three-dimen-sional (3D) viewing by moving a selector switch thatchanges the optical path projected to the trinocularport. The Wild M400 has a single optical path that isperpendicular to the stage. This eliminates the lateralshift problems encountered as one adjusts the micro-scope stage in systems with angled optical paths. Thedownside to both of these microscopes is their age.Even though they are built to last several lifetimes,their scarcity can make it difficult to source desirableaccessories such camera adapters, 2× objectives, andmodel-specific polarizing filters.

DIGITAL CAMERASSince the inception of the digital camera concept in1972 (Trenholm, 2007), it has been a long road to de-velop the technology that would surpass the qualityof film. This development in digital imaging has es-sentially been the death of film photography; the onlypractical option for photomicrographers today is toadapt their microscope to a digital camera. One of themost significant benefits of the digital age is that pho-tography has become much more cost effective, allow-ing many more people to enjoy this rewarding hobby.Previously, the cost of purchasing and developinghigh-quality film could be as much as $2–$3 per finalbracketed image (J. Koivula, pers. comm., 2014). Now,the photomicrographer can capture as many imagesas desired at no additional expense. This facilitates re-peated practice, as one does not have to be concernedwith the cost of film “waste.”

Modern digital cameras with complementarymetal oxide semiconductor (CMOS) sensors offer ex-cellent color rendition, very high resolution capabil-ity, and a tremendous amount of control over manyparameters, including shutter speed, white balance,International Organization for Standardization (ISO)settings, and exposure compensation. While budgetis important when choosing a camera for photomi-crography, other factors to consider are resolution,weight, vibration control, and remote control capa-bility. Camera choices can be as simple as the digitalcamera on your smartphone (Boehm, 2014) all theway to a professional-grade digital single-lens reflex(DSLR) camera. The author currently uses a Canon6D DSLR. Several notable features are the high-res-olution, full-frame (36 mm × 24 mm) sensor and Wi-Fi capability for wireless remote shooting, whichhelps to eliminate potential image-blurring vibra-tions. This particular camera is also appealing be-

cause of the lightweight composite body, comparedto other DSLR full-frame cameras with heavier alloybodies, helps to prevent the focusing rack from be-coming overloaded, making it easier to maintainimage focus. Many of these features can be found onother DSLR cameras as well; this model serves as anexample of criteria to consider when selecting a cam-era for photomicrography.

ADAPTING A DIGITAL CAMERA TO A MICROSCOPEOne of the biggest challenges in adapting almost anymicroscope for image capture is mating the camerato the microscope so that it is parfocal. This is whenthe image at the camera sensor is in focus at thesame time as the image viewed in the microscope oc-ulars. Parfocality makes image composition mucheasier and saves significant time. Certain manufac-

turers of specialty adapters offer ready-made solu-tions for camera adaptation, but some microscopesmay require additional components to achieve par-focality. The author’s Nikon SMZ10 was mated to aDSLR camera by using a Diagnostic InstrumentsPA1-12A adapter tube with a helicoid-style extensiontube for parfocality adjustment; this was then con-nected to a Canon adapter for the camera (figure 4).

Once the camera is selected and attached to themicroscope, there are additional considerations re-garding the relay lens in the trinocular port. The pri-mary factor that should influence your choice ofmagnification of this optical element is the sensorsize of your camera. The best choice of relay optic isone that completely fills the sensor (to avoid vi-


In Brief • The development of digital camera technology hasmade photomicrography more accessible and afford-able than in the past.

• High-quality used microscopes are better suited forphotomicrography than inexpensive newer models.

• DSLR cameras can produce images that rival the qual-ity of film and are well suited for capturing photomi-crographic images.

• Software such as Helicon Focus and Adobe Photoshopare powerful tools that can be used to get the best re-sults from digital photomicrography.

gnetting, or fuzzy dark edges) and does not waste toomuch light through over-magnification as the imageis projected on the camera sensor.

For microscopes without a trinocular port,adapters that mount the camera onto an ocular pres-ent a very reasonable solution (figure 5, left). Sincetraditional observation is not possible in this config-uration, the photomicrographer must rely on a liveview displayed on a monitor to set up the specimen(figure 5, right). With the significant advances insmartphone cameras, it is possible for the hobbyistto take decent-quality photomicrographs with thesedevices (Boehm, 2014). Inexpensive products to facil-itate smartphone photomicrography also exist (Over-ton, 2010). The most obvious advantage tosmartphone photomicrography is portability, a sim-ple matter of carrying a smartphone and a loupe inthe field (Boehm, 2014).

GETTING STARTED: CLEANING AND VIBRATION CONTROLTwo important considerations for photographythrough the microscope in achieving satisfactory re-sults are sample cleaning and vibration control(Koivula, 1981). A clean sample simply makes amuch more striking image. If one is investing thetime required to take a high-quality photomicro-graph, the results are dramatically improved if sometime is spent properly cleaning a sample prior to set-ting up the image. Typically, this can be accom-plished with a stone cloth and a damp sponge toremove as much dust and finger oil as possible. Thiswill save significant time in post-capture image pro-cessing and dust spot removal, which will be dis-cussed later in the article.

Vibrations can cause loss of detail by blurring animage. This happens when subject movement occurs


Figure 4. A helicoid-style extension tubeeasily allows for upand down movement ofthe camera in orderachieve parfocalitywith the microscope oc-ulars. Photos byNathan Renfro.

Figure 5. Left: A camera adapter that slips over the microscope’s ocular can turn a binocular microscope into aphotomicroscope, as seen on the author’s GIA Gemolite Mark V. Right: A live view shown on a computer monitoris used for focusing and composition because the oculars are blocked by the camera. The camera is remotely con-trolled by the software, which helps prevent vibration-induced blurring that would occur by manually pressing theshutter button. Photos by Nathan Renfro.

over the exposure time. Two solutions for this prob-lem are eliminating causes of movement or decreas-ing exposure time. By making the microscope morerigid or isolated from the environment, the photomi-crographer minimizes vibration-induced problems.A floating optical table is best, but this is generallytoo expensive for hobbyists. To help eliminate vibra-tional movement, one can add shock-absorbing anti-vibration mounts or rubber pads underneath themicroscope to help prevent vibrations from reachingthe subject.

Another solution to help eliminate vibration-in-duced blurring is to decrease the exposure time sothere is less chance for the subject to move. With dig-ital photomicrography, you can increase the lightsensitivity of your camera by adjusting the ISO set-ting, the modern equivalent to the American Stan-dards Association’s (ASA) “film speed.” If yourcamera is more sensitive to light, then the requiredexposure time decreases; however, if the ISO is ad-justed too high, image quality may suffer from whatis known as “noise” or a grainy salt-and-pepper typeappearance.

For users of DSLR cameras in particular, the mir-ror and shutter movements may cause some addi-tional vibrations. If selecting a DSLR digital camerafor photomicrography, it may be worthwhile tochoose one with a “silent shutter” mode, which willgreatly reduce camera-induced vibrations.

LIGHTING TECHNIQUESLighting is the single most important factor in takinga high-quality photomicrograph. Without proper il-lumination, satisfactory results will never be

achieved. Most gemologists are familiar with severaltypes of broadly suitable lighting. Brightfield, dark-field, and reflected light are the types of illuminationtypically used in gemology. There are several othertypes of environments or modifications to thesetypes of light that will greatly enhance the appear-ance of almost any photomicrograph. The difficultyis in knowing which type of lighting or combinationof lighting to use for a given inclusion scene. Thisvaluable insight, which must be learned throughreading literature on photomicrography and signifi-cant practice, has been extensively covered (Koivula1981, 1982a, 1982b, 1984, 2003).

Darkfield illumination is probably the most fa-miliar type of lighting for general observation, be-cause most gemological microscopes are equippedwith a darkfield base. This type of lighting allowslight-scattering inclusions to stand out in high reliefagainst a dark background and can be useful for high-lighting small inclusions (figure 6, left). While thislighting environment is useful for general observa-tion, the high degree of contrast produced betweenthe inclusions and background is not always desir-able or aesthetically pleasing. One important consid-eration in darkfield photomicrography is thatundesirable dust particles and surface scratches willbe conspicuous, which may limit this lighting envi-ronment in all but the most pristine of specimens.

Brightfield illumination, or transmitted light, is atechnique in which the specimen is placed betweenthe objective and a bright direct illumination source(figure 6, right). This type of lighting is particularlyuseful for examining color-zoned specimens andmasking the appearance of fine dust particles; how-


Figure 6. This cinnabar inclusion in barite is shown using darkfield (left) and brightfield (right) illumination. Pho-tomicrographs by Nathan Renfro, field of view 2.88 mm.

ever, detail may be lost when examining overly darkor opaque inclusions. Brightfield illumination can befurther enhanced by using a diffuser plate to controlthe light intensity if direct transmitted light sacri-fices too much detail by creating bright reflectiveareas, sometimes called “hot spots” (Koivula, 2003).

Diffuse reflected light is useful for examining sur-face features and revealing differences in luster be-tween two dissimilar materials. This lighting is alsosuitable for detecting coatings, as they often displaya higher luster than the substrate material.

Fiber-optic illumination may be the most under-used and single most useful form of illumination ingemology. Quite often, crystallographically-orientedinclusions can be well hidden unless an illuminationdirection can be achieved to facilitate light scatterfrom these particles. Because of the widely adjustableposition of the fiber-optic illuminator, hidden inclu-sions are often easily revealed (figure 7). When usinga fiber-optic illuminator, controlled light can beguided to the subject at an oblique angle to highlightany unseen iridescent components (figure 8; Koivula,1982a). Crystallographically-oriented thin film inclu-sions are often particularly responsive to obliquefiber-optic illumination (Koivula, 1980), revealingvivid colors when this method is used (figure 9).

While the use of polarized light is quite familiarto most gemologists by way of the polariscope, usingpolarized light in conjunction with the microscopemay be foreign. The most significant use of a polar-izer in gemological photomicrography is the elimi-nation of doubling in birefringent materials byplacing a polarizing filter, called an analyzer, betweenthe objective and the subject (figure 10). This polar-

izing filter will eliminate one of the refraction direc-tions, thereby making the image appear singly refrac-tive. Crossed-polarized light, created by addinganother polarizing filter between the subject andlight source oriented 90 degrees to the plane of polar-ization of the analyzer, can also reveal low-relief,nearly invisible inclusions in high contrast due tostrain and optical misalignment. Also, the vibrantcolors occasionally observed from birefringent inclu-sions in polarized light are a welcome sight to almostany photomicrographer (figure 11). Polarized lightcan be further enhanced by the use of a first-order redcompensator. Also known as a full-wave plate, this


Figure 7. Thin, reflective, oriented fluid inclusions, as seen in this aquamarine (left, vertical field of view 2.54 mm)and covellite in this pink fire quartz (right, 6.13 mm vertical field of view), often reveal vibrant displays of colorunder oblique fiber-optic illumination. Photomicrographs by Nathan Renfro.

Figure 8. Oblique fiber-optic illumination can be usedto reveal iridescent colors in reflective inclusions thatmight go otherwise unseen. Photo by Nathan Renfro.

type of filter significantly decreases the exposuretime required to capture an image in polarized lightand can dramatically enhance strain color (figure 12)(Koivula, 1984).

Ultraviolet (UV) light has limited but occasionaluse in photomicrography. UV illumination can in-duce a fluorescent reaction in certain subjects, pro-ducing visually striking results that can bephotographed (figure 13); however, exposure timesgreatly increase, as the lumination intensity is typi-cally far less than any other lighting environmentmentioned. This increased exposure time may leadto vibration-induced blurring of images. Also, it

should be noted that UV light may be harmful to thephotomicrographer’s eyes, so exposure should bekept to a minimum and proper protective equipmentshould always be used.

The photomicrographer will quickly realize thatsometimes no single type of lighting is adequate toproduce a high-quality photomicrograph for a partic-ular specimen. Significantly more impressive resultsmay be produced using combinations and/or modifi-cations of the lighting previously mentioned. Learn-ing which combinations to use and when to usethem is an important skill developed with practice.Once the correct illumination sources are selected,


Figure 9. Viewed only with shadowed brightfield lighting, this partially healed cleavage crack looks rather ordi-nary. With the addition of oblique fiber-optic illumination, unexpected interference colors caused by thin film iri-descence are revealed. Photomicrographs by Nathan Renfro; field of view 2.96 mm.

Figure 10. Left: Because of birefringence in anisotropic materials such as tourmaline, image doubling is often aproblem, as revealed by these apatite crystals. Right: A polarizing filter placed between the objective lens and thesubject, rotated to the appropriate position, does away with image doubling by eliminating one of the birefringentlight paths. Photomicrographs by Nathan Renfro; field of view 1.50 mm.

the next challenge is controlling the light in order tobalance the contrast in an image and resolve themost detail. One of the biggest problems in lightingis controlling hot spots. A useful technique utilizesa piece of opaque black paper (or similar material)carefully inserted to block the precise source of lightcausing the hot spot without blocking the desirablelight that is illuminating the subject (Koivula, 2003).Another lighting modification is a similar, carefullycontrolled approach of contrast enhancement called“shadowing” (Koivula, 1982b). Shadowing effectsprovide a tremendous amount of contrast in inher-ently low-contrast specimens by adding dark areas tootherwise light subjects (figure 14). To create shad-owed illumination, an opaque black paper or similarmaterial is slowly moved in between the illumina-

tion source and the specimen until contrast and de-tail are at a maximum (see again figure 14). Thisshadowing technique can be applied to darkfield,brightfield, and even reflected light environments.

DIFFERENTIAL INTERFERENCE CONTRASTA remarkable lighting technique that has only occa-sionally been applied to gemology is episcopic differ-ential interference contrast (DIC). This reflected light,contrast-enhancing technique (Koivula, 2000) has pro-duced some of the most vibrant displays of color andgeometric patterns ever observed in gemology. A spe-cialized microscope equipped with a Nomarski-mod-ified Wollaston prism and polarizing filters is requiredfor this type of microscopy (figure 15). Sheared wavefronts created by the prism are focused on the speci-


Figure 11. Left: This rock crystal quartz host, as seen in transmitted light, shows low-relief, colorless, needle-likeamphibole inclusions. Right: When the same field is observed with polarized light, the amphibole inclusions standout in a vivid display of interference colors. Also, a nearly invisible inclusion of quartz reveals its crystallographicmisalignment in polarized light. Photomicrographs by Nathan Renfro; field of view 5.10 mm.

Figure 12. This spinel hosting a carbonate crystal, as seen in brightfield (left), shows significant anomalous doublerefraction, or strain, under crossed polarized light (center). This strain is further enhanced by using a first-order redcompensator in the optical path, which adds a blue color component to the strain and also decreases the exposuretime required to capture the image (right). Photomicrographs by Nathan Renfro; field of view 2.20 mm.

men by the objective and travel slightly different pathlengths due to the surface topography of the specimen.These variations in topography are transformed intoamplitude or intensity variations, revealing the topo-

graphic profile of the specimen (Brandmaier et al.,2013). DIC microscopy is capable of yielding bothgrayscale images and “optically stained” full-color im-ages by simply adjusting the position of the prism in


Figure 13. This tabular negative crystal in quartz was photographed with diffuse transmitted light (left), long-waveultraviolet light (center), and a combination of visible and LWUV light (right). Each image produces a strikinglydifferent result, demonstrating the interesting results attained through combination lighting. Photomicrographs byNathan Renfro; field of view 1.24 mm.

Figure 14. Transmitted,diffuse lighting (top left)is used to photograph anepigenetic malachite disc(Renfro, 2013), approxi-mately 0.58 mm in diam-eter (top right). Thislighting is ideal whenphotographing colored in-clusions, but contrast issignificantly diminished.Placing a black strip ofopaque material betweenthe light source and thesubject (center left) cancreate a shadowing envi-ronment, significantlyenhancing contrast in thesubject and giving rise topreviously unseen detail(center right). Differentlyshaped tools can be usedto create various shadoweffects, as seen when asmall iris diaphragm(bottom left) is used tocreate a circular shadow-ing environment (bottomright). Photos and pho-tomicrographs by NathanRenfro.

the optical path (figure 15). The surfaces of highly-re-flective mineral inclusions can also be carefully exam-ined through their host mineral using DIC (figure 16);however, this technique is not always possible for sub-surface inclusions if they are located too deep in thehost material, or if the host is too reflective.

DIGITAL IMAGE PROCESSINGIn addition to the previously mentioned advantages,digital photography also allows for a wide range ofpost-processing tools that can improve image appear-ance. While software makes it possible to modify im-ages to the point that the image does not accuratelyrepresent the subject, the goal of gemological pho-tomicrography is to document inclusions as realisti-cally as possible. Therefore, it is not useful todigitally modify images beyond their natural ob-served appearance. Software enhancement thatmakes images appear as close to the actual subject aspossible is a tremendously useful tool that, when ap-plied appropriately, is very welcome in the digitalphotography world. Two particularly importantimage-processing tools are extended depth-of-field,also called “extended depth of focus” or “focus stack-ing” and high dynamic range (HDR) imaging.

In an extended depth-of-field, is when a series ofimages are captured at regularly spaced focal planesand digitally combined to extend the depth-of-field

beyond what is possible in a single image (figures 17and 18). This is particularly important for photomi-crography at high magnification, since depth-of-fielddecreases at higher magnification. This digital pro-cessing technique allows the photomicrographer tocapture inclusion scenes with tremendous detail athigh magnification that would otherwise be impos-


Figure 15. These differen-tial interference contrastimages show a variety ofinteresting surface struc-tures, including (clockwisefrom top left): the etchedsurface of a diamond crys-tal from Wyoming (field ofview 0.25 mm); the etchedprism face of an emeraldfrom North Carolina (fieldof view 0.62 mm); the sur-face of an Australian opalwith pyrite inclusions thatbreak the surface, leavingdrag lines from the polish-ing process trailing behind(field of view 1.24 mm);and plasma etching ontwo pavilion facets of a“fire polish”diamond(field of view 0.62 mm).Photomicrographs byNathan Renfro.

Figure 16. Even subsurface inclusions, such as thisplaty hexagonal metal sulfide crystal in a rock crystalquartz host, can be examined using DIC. Photomicro-graph by Nathan Renfro; field of view 0.25 mm.

sible in a single frame image. There are several pro-grams to facilitate focus stacking, including ZereneStacker (Prince, 2014), Helicon Focus, and NIS Ele-ments. One requirement is that the image set mustbe stepped at fairly regular intervals. While it is pos-sible to slowly turn the focus knob on a microscopeby hand, it is impractical to do so in regular incre-ments without some way to measure each step. Theaddition of a dial indicator or similar measurementdevice on the microscope focusing rack may be acost-effective solution, allowing regular focus inter-vals to facilitate extended depth-of-field imaging (fig-ure 19, left). A focus mount with a fine adjustmentwill also help the user precisely index the focusheight. More sophisticated solutions may involve afocus rail with a stepper motor, which can be digi-tally controlled through a compatible software pro-

gram to index the microscope focus at very precise,regular intervals (figure 19, right). This equipment isparticularly useful for very large depth ranges, whichwould require many images.

HDR is another useful processing technique. Indigital photomicrography, reflections from facets andother inclusions can create scenarios where someareas of the image are beyond the dynamic range ofthe camera sensor. In other words, the difference be-tween the lightest and darkest areas in the inclusionscene is beyond what the camera sensor can measurein a single image. The most effective approach is toeffectively control the illumination source so that alllighting that falls in the image frame is within thecamera’s ability to capture. Another consideration isadjusting the camera’s ISO setting to the lowest pos-sible value. This typically allows the camera to op-


Figure 17. These fluid-fillednegative crystals in rockcrystal quartz were pho-tographed using an extendeddepth-of-field to achieve animage with sharp focus. Theleft-hand image shows theforeground in focus while thebackground inclusions areblurry. The center imageshows the background infocus while the foreground isblurry. Approximately 30images stacked together pro-duced an entirely in-focusimage of the cluster, as seenon the right. Photomicro-graphs by Nathan Renfro,field of view 6.55 mm.

Figure 18. This chalcedony contains bands of hematite and goethite clusters scattered throughout a very largedepth-of-field. To get the entire image in focus, extended depth-of-field imaging was used, composing 40 images atdifferent depths (left and center) and stacking them together with software to produce and entirely in focus image(right). Photomicrographs by Nathan Renfro; field of view 8.70 mm.

erate at the largest possible dynamic range. HDR im-aging can help combat the appearance of overly brightor dark areas in an image when lighting cannot be con-trolled to eliminate loss of detail. Similar to focusstacking, the photomicrographer must capture severalimages that are combined into one final image. Instead

of changing the focus, as with image stacking, the ex-posure time is changed. Details resolvable at severaldifferent exposures are combined into a single imagethat is beyond the detail possible from any single ex-posure. Sometimes this effectively reproduces whatthe gemologist actually sees when observing the spec-imen in the microscope. The human brain and eye donot suffer from the relatively narrow dynamic rangeof a digital camera sensor, so in some cases, a high dy-namic range image may approximate the actual sub-ject than any single exposure alone (figure 20). HDRimaging can be accomplished using software designedfor this task, often available on the Internet, such asNikon NIS Elements, Canon Digital Professional,Oloneo HDR, and Photomatix Pro. Some camerashave built-in HDR processing capabilities, includingmany smartphones and some Canon and NikonDSLR cameras. This convenient built-in feature helpsautomate HDR imaging without the need for second-ary image-processing software.

Other types of post-processing digital image soft-ware help the photographer make fine adjustmentsto the captured image. Sometimes the settings usedto capture an image can be improved. Unlike film-based photography, the digital world offers tools tomodify brightness, contrast, and color without hav-ing to retake a photograph or take several exposuresat different settings to see which one looks best.Some digital software also offers enhancement toolsthat clean up images and remove artifacts such asminute spots of dust on the sample or spot artifactsfrom dust on the camera sensor (figure 21). These toolshelp photographers adjust images to more accurately


Figure 19. A digital indicator was attached to the au-thor’s microscope stand to accurately measure thestep intervals for extended depth-of-field imaging.Left: The fine focus adjustment allows the microscopeheight to be precisely controlled to step intervals assmall as 2.5 microns. Right: Sophisticated equipmentsuch as this “Macrorail” can be used for automatedimage stacking when combined with the appropriatesoftware. Photos by Nathan Renfro (left) and DarrenBates (right).

Figure 20. These radial manganese oxide “flowers” in Ethiopian opal provide too much contrast for the camerasensor to resolve all of the detail in the inclusion. The image at the left was underexposed, so detail is lost in thedark center of the MgO flower. The center image was overexposed to resolve detail in the dark areas, but all detailis lost in the bright areas. These varying exposure images were combined using HDR software (Nikon’s NIS Ele-ments) to produce the image on the right, which shows more detail than any single image. Photomicrographs byNathan Renfro; field of view 2.47 mm.

represent their subjects. The most popular of theseprograms is almost certainly Adobe Photoshop, butmany photography-specific post-processing programshave been developed with the onset of digital photog-raphy. Photoshop Lightroom is also a popular optionfor image post processing and organization, but otherprograms such as Pixelmator (for Macs and iPads) andGIMP (GNU Image Manipulating Program) offer easy-to-use digital image correction tools. Photomicrogra-phers will also want to consider the file type. Raw filesare much larger than JPEG files, but also better forpost-image processing adjustments.

SUBJECT SIZEOne of the most important attributes conveyed by aphotomicrograph is the size of the subject. There area few ways to present this information: indicating

the magnification used to capture the image for a par-ticular format (size of the camera sensor), overlayinga scale bar onto the image itself, or indicating thefield of view as a numerical measurement. Gemolog-ical texts have historically indicated the magnifica-tion that was used to observe a subject to convey therelative size of the inclusion scene and how it wouldlook in the reader’s own microscope. The rationalehere is that most gemologists are familiar with themagnification range used during routine gemologicalmicroscopy, which may not be true of a numericalvalue presented in a possibly unfamiliar unit, suchas microns. The biggest problem with using magni-fication in the digital age is maintaining accuracyduring the post-processing phase, as images are oftenformatted and cropped in ways that render the origi-nal magnification meaningless.


Figure 21. Fine dust spots (top left, field of view 6.95 mm) on the surface of this chalcedony with carbonate inclu-sions from Turkey detract from the interesting inclusion scene. Image editing software such as Adobe Photoshophas touch-up tools that allow digital removal of dust spots and unwanted minute artifacts, as shown in the editedimage (top right, field of view 6.95 mm). Zooming in on the top right portion of the image with significant dust(bottom left, field of view 3.10 mm), the difference before and after dust removal with Adobe Photoshop is muchmore apparent (bottom right, field of view 3.10 mm). Photomicrographs by Nathan Renfro.

The magnification factor of an optical microscopeis determined by multiplying the magnification fac-tors of all optical components between the specimenand the observer’s eye. While this represents the ob-served magnification, the actual magnification of therecorded image can vary depending on the size of thecamera sensor, and will likely be very different fromthe observed magnification factor. The easiest methodto determine the magnification at the camera sensoris to use a microscope calibration slide (figure 22) todetermine the actual field of view the camera cap-tures. If the field of view and the physical size of thecamera sensor are known, then the magnification fac-tor at the camera sensor can be calculated by dividingthe sensor width by the horizontal field of view of thesubject as measured by the calibration slide. Thisrecorded magnification becomes meaningless as soonas the image is cropped or enlarged from the originalfootprint of the camera sensor, which will almost cer-tainly occur. This is why a more precise way to com-municate the actual size the photomicrographrepresents is needed. This can be accomplished by theuse of a scale bar or a field of view measurement.

In most scientific publications, scale bars are usedto indicate subject size by overlaying a line of knownlength on some portion of the photomicrograph(Hord, 2004). This is an accurate way to convey sub-ject size in a photomicrograph. Some software, suchas Helicon Focus, provides a tool that lets the user

quickly add a scale bar to their images. Despite thebenefit of the information they contain, scale bars doobscure a portion of the image. Gemology is an ob-servational science, and gemologists are privileged toview beautiful scenes that are preserved in photomi-crographs. The artificial addition of a scale bar maybe perceived as an unnecessary blemish on an other-wise artistic scene, which is reason enough for thisauthor to exclude scale bars. Fortunately, there is acompromise that overcomes the problems withusing magnification and scale bars to convey subjectsize: expressing a field of view measurement for thefinal image in the caption. This offers an accurate ac-count of subject size without marring an otherwisepristine inclusion scene with an unsightly scale bar.

CONCLUSIONPhotomicrography is a tremendously rewarding as-pect of gemology. It appeals to all types of practition-ers, from scientists to artists and everyone in between.With technological developments in the last decade,digital-format photography has spurred the develop-ment of a wide range of tools to enhance images inways never before possible. Digital photography hasalso helped to offset cost-related issues, since thereare almost no consumable items that the photomi-crographer must purchase after an initial investmentin equipment, allowing many more people to partic-ipate in this branch of gemology.


Figure 22. A microscopecalibration slide, suchas the one manufac-tured by Bausch andLomb Optical Co., canbe used to determinethe actual field of viewof an image takenthrough the micro-scope. Photo by Robi-son McMurtry.

Because of the spectacular level that digital tech-nology has already achieved in the last decade alone,it is hard to imagine how photomicrography mightevolve in the next 10 years. One area with significantroom for improvement is lighting options. Light-emitting diode technology is improving at a rapidrate, and the implementation of LED lighting in pho-tomicrography will be a welcome improvement, asit comes closer to “natural-looking” full spectrumlighting. Camera technology will likely continue toimprove as higher-resolution and higher-sensitivitysensors are developed. Canon recently announced

the release of a full-frame DSLR with more than 50megapixels of resolution, the highest of any 35mmformat camera to date (Canon, 2015). Two models,the 5DS and 5DSR may prove to be well suited forphotomicrography. Vibration may also be curtailedas mirrorless digital cameras become more refined.Hopefully, the overall cost of digital camera equip-ment will be lower, allowing more users to acquirebetter equipment and capture better images.

With practice and patience, anyone can enjoy thisbranch of gemology and share their observations anddiscoveries within the micro-world of gems.


ABOUT THE AUTHOR

Mr. Renfro is the analytical manager of the gem identification de-partment, and analytical microscopist of the inclusion researchdepartment, at GIA in Carlsbad, California.

ACKNOWLEDGMENTS

The author would like to thank Gene Goldsand, Danny J.

Sanchez, Kevin Schumacher, and Eric Welch for their helpful discussions regarding equipment and software. The author alsothanks Shane McClure for several helpful recommendations onthe composition of gemological photomicrographs. Lastly, the author thanks John Koivula for the continued mentorship,friendship, and overwhelming support that made this articlepossible.

Boehm E. (2014) Photomicrography using a smartphone camera.The Journal of Gemmology, Vol. 34, No. 1, pp. 6–7.

Brandmaier C., Spring K., Davidson M. (2013) Reflected lightDIC microscopy, http://www.microscopyu.com/articles/dic/reflecteddic.html

Canon (2015) Canon U.S.A. introduces the world’s highest reso-lution full-frame DSLR cameras: EOS 5DS and EOS 5DS R.Press release, Feb. 5.

Gübelin E., Koivula J. (1986) Photoatlas of Inclusions in Gem-stones, Volume 1. ABC Edition, Zurich.

——— (2005) Photoatlas of Inclusions in Gemstones, Volume 2.Opinio Verlag, Basel, Switzerland.

——— (2008) Photoatlas of Inclusions in Gemstones, Volume 3.Opinio Verlag, Basel, Switzerland.

Hord B. (2004) Letters: Expressing magnification in photomicro-graphs. G&G, Vol. 40, No. 3, p. 199.

Koivula J.I. (1980) “Thin films”—Elusive beauty in the world ofinclusions. G&G, Vol. 16, No. 9, pp. 326–330.

——— (1981) Photographing inclusions. G&G, Vol. 17, No. 3, pp.132–142.

——— (1982a) Pinpoint illumination: A controllable system oflighting for gem microscopy. G&G, Vol. 18, No. 2, pp. 83–86.

——— (1982b) Shadowing: A new method of image enhance-ment for gemological microscopy. G&G, Vol. 18, No. 3,

pp. 160–164.——— (1984) The first order red compensator: An effective gemo-

logical tool. G&G, Vol. 20, No. 2, pp. 101–105.——— (2000) The Microworld of Diamonds. Gemworld Interna-

tional. Northbrook, Illinois.——— (2003) Photomicrography for gemologists. G&G, Vol. 39,

No. 1, pp. 4–23.Koivula J.I., Kammerling R., Fritsch E., Eds. (1994) Gem News In-

ternational: Amber marketed with photomicrography. G&G,Vol. 30, No. 2, p. 124.

Overton T.W. (2010) Gem News International: Smartphone pho-tomicrography. G&G, Vol. 46, No. 4, pp. 325–326.

Prince N. (2014) Use of stacking software for expanding depth-of-field in inclusion photomicrography. The Journal of Gemmol-ogy, Vol. 34 No. 3, pp. 188–189.

Renfro N.D. (2013) Gem News International: Unusual epigeneticmalachite discs in quartz. G&G, Vol. 49, No. 3, pp. 178–179.

Shipley Jr. R.M. (1939) United States Patent Office, Dark Field Il-luminator, Patent number 2,157,437.

Trenholm R. (2007) Photos: The history of the digital camera, Nov.2, http://www.cnet.com/news/photos-the-history-of-the-digital-camera.

REFERENCES

Documents

DIgital Photomicrography for Gemologists · most significant benefits of the digital age is that pho - tography has become much more cost effective, allow - ing many more people to