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Ph o to g r ap h y o fG ea r Fa i l u r es

m hotography is an essential partof ge.ar failure analysis. Itnotonly provides a fast, conve-nient way to accurately docu-ment the appearance of gear failures,but also is an effective diagnostic toolbecause the magnification obtainedthrough photographicenlargementand slide projection often disclosesevidence that may have been missedif the gears were not photographed.lam not a professional photogra-

pher, however, [ find it necessary todo my own photography. It has onlybeen by personally composing thephotograph through the cameraviewfinder that the photographs showthe particular detail Iwish to capture.While there are a multitude of

ways to obtain good photographs anda huge array of photographic equip-ment to choo e from, what follows isa description of equipment and tech-niques that Iuse for field and studiophotography of gear failures. It is aproven system that has the followingfeatures: All equipment is lightweight and

readily portable (easily carried onboard aircraft); All equipment is robust enough

to withstand the rigors of harsh indus-trial environments; The technique is easily learned

and can be relied on to produce goodphotographs consistently.

The BasicsThe equipment nece sary for gear

failure photography i not elaborateand is readily available at good cam-

R o b e rt E r ri c h eU o

era stores. It consists of the camera,lenses, and a tripod. The subject ofwhat kind of lighting to use and whenwill be discussed later in the article.

Camera. Most of the features ofnewer, computerized cameras are notnecessary or do not work well forphotographing gears. Ihave foundthat auto-focus cameras are not suitedto the macrophotography of gearsbecause the light reflected from shinysurfaces. of gear teeth te nd s to confusethe computer. Almost any manual, 35mm single lens reflex. (SLR) camerabody with quality lenses can be usedfor photographing gears. Ise a man-ual Pentax SP 1000, SLR camerabody that is an early version of thePentax K- lOOO .

Tripod_ For overall photographs Iprefer to rely on ambient lighting,which usually requires relatively longexposures. With macrophotography,the lens needs to be stopped down illorder to maintain the depth of field,which aJ 0 requires long exposures.Therefore, a good tripod is a necessityto avoid camera-shake.I use a Benbo Trekker 35 tripodwith a pan-ballhead. Itis compact and

weighs less than five pounds. It isunique because the legs can be posi-tioned at an y angle, and it features aspecial monorail. that allows you toraisevlower, extend, retract, twist orangle the camera without changing thetripod position. The flexibility i s e sp e-ciallyunportant for macrophotogra-phy because the working distancesbetween the camera, umbrella, lamp

Address your g'earing ques-tions to our panell 0 1 experts ..W rite to them care of S ho'pFloor. Gear TechnollogiY. i P . O .B.ox 1:426.,El lk Grove Village,IL 60009. er call our editoria ,lstalff at (708)437~6604 ..

H o b e r t E n i c h e ll ois the principal in GEARTECH. a gear consultingfirm and founder ofGEARTECH Software,lnc., in Albany, CA. He isalso a writer and instruc-lor 011 gear design. analy-sis and application sub-jeers. He is a member ofASME. AGMA. STLE. anda Registered ProfessionalEngineer ill the State ofCalifornia.

I,IARCHIAPRIL 1994 4 3 ,

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and subject are small, and the camerais usually the easiest item to adjust.The tripodadjusts easily to uneventerrain because each leg can be indi-vidually adjusted. This feature is espe-cially important for photographinggears om-site where there may be lim-.ired space and no flat surfaces.

Lenses. ~f in d th at three lenses aresufficient for most of my failureanalysis work. I use a 55 mm normallens for mast of the overall pho-tographs of large gears and gearboxes ..When there is not enough roam toback away from the subject to includeeverything in the photograph, I use a35 mm wide-angle lens. Far dose-upphotographs of individual gear teeth, Iuse a 90 mm macro lens.

Macrofenses. Macrolensesareoptically corrected for shooting atclose range. Fixed-focal-lengthmacrolenses have the best imagequality. Macro/zoom lenses can focuscloser than fixed-focal-length lenses.but they are not specifically designedfor close-up work, and their imagequality is not as good.Fixed-focal-length lenses vary

from about 50 mm to 200 mm.Longer focal lengths allow extraworking distance between the lensand the subject. I use a Tamron SP 90mm f/2.S macrolens, The 90 mm focallength gives a minimum working dis-tance of about 215 mm from the endof the lens to the subject. (about 125mm with. extension tube).The degree of magnification with

macrolenses is specified a a magnifi-cation ratio, which is the ratiobetween the size of the subject'simage on film and its real size. Mostmacrolenses have a magnificationratio of 1:2, which gives a film imagethat is 112 the real. size. With anextension tube, the magnificationratio is increased to I: 1, giving a filmimage the same size as the subject.

Lighting The SubjectGear teeth are hard to photograph

properly. especially if they are highly4 4 GE ....R TECI-INOLOGY

polished, because light reflectingfrom shiny surfaces causes "hotspots" in the photograph that obliter-ate details. Camera-mounted flash-guns are especial.ly problematicbecausethe light is reflected off hinysurfaces directly into the lens. Someimprovement is obtained by using anextension cord and holding the flash-gun to the side at an angle so thatreflected light is directed away fromthe lens, hut there is no sure way toknow where to place the flashgun.The basic problem with flashguns

is that they emit a point source of veryharsh light.. Adding diffusers to theflash help to soften the light, but thelighting is still too harsh because itoriginates from a Ingle point. Whitecard can be used to bounce the lightfrom the flashgun. which in effectincreases the number of light sources,but the results are still unpredictable.A ring flash is an improvement

over a flashgun because it surroundsthe lens with a ring of even light thatis relatively soft . .The ring fla h elimi-nates hot spots in most cases. exceptfor mirror-like subjects. such as bear-ing raceways.The performance of a flash can beimproved immensely by directing thelight into an umbrella that reflects thelight back to the subject. In effect. thesource of the light is increased to thesize of the umbrella. and the light isdiffused and softened.

Tungsten Ligluing ..A major dis-advantage of flash photography isthat the lighting cannot be previewedby looking through the viewfinder.The solution is to eliminate the flashand substitute a tungsten lamp. Withthe light from the tungsten lampreflected from an umbrella, the pho-tograph can be composed through theviewfinder, and the photographer cansee exactly what the photograph winshow. Shadows are easily controlledby moving the umbrella or subject,and fill light can be added by usingwhite cards. I find that the umbrella

and tungsten lampeliminate hot spotsby providing soft, even illuminationthat result in photographs that arerealistic and pleasing. The only dis-advantage of the tungsten lamp is thatit is hot and can be uncomfortable atclose working distances .

Overall PhotographyFor overall photos of the entiregearbox or other large equipment. I

u e a 55 mm normal lens or a 35 rnmwide angle lens. Iprefer to use ambi-ent lighting where possible because it

SHOPFLOORB as ic Eq u ip m en t fo r

G ear F ai lu r e P h ot og ra ph yWhat fo llows is a lis t o f my "pe rsonalfavorites' in terms of equipment. Other,comparable equ ipment is on the mar-ket, a nd readers a re encouraged tolook for that which works bestfor them. C amera - P entax SP 1000, 3 5mm SL R

T ripod - B enbo T rekker 35 withpan-balihead

N ormal lens - T akumar 5 5 mm W ide angle lens - T amron 35 mm M acrolens - T amron SP 90 mm

f/2.5 with extens ion tube T ungsten lamp - Lowel T ota-Light, 1000W

Umbrella - P h otek GoodliterStowaway

L ight s ta nd - P hoto flex L ites ta nd C olor slide film - K odakEktachrome 320T Professional,ISO 32 0

C olo r print film - F ujic olo rReala .SO 100

G ray card - Kodak 8 x 1 0 in.gray card

Color card - J obo F ilters - No. 80A and skylight IAsky light filte r is a c lear g la ss cove ryou may wish to pu t ove r your lensesto prevent scratches on them. A newlense may cost upwards of $100 ; askylight f ilter costs less than $10.) R ing flash - S unpak auto O X 8R F lashgun - V ivitar 2 83w ith S 8-4powe r supply and fla sh cord

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allows composition of the photographthrough the lens, Ambient lightingavoids problems associated with flashphotography, uch as "hot spots" orover! y dark backgrounds. Manyindustrial sites have fluorescent lightswh ic h c re ate p ro bl em s for most colorfilms. However, Fujicolor Reala filmgives excellent color reproduction,even with fluorescent lighting. Thefilm speed is [SO 100, which is rela-tively slow, and itrequires long expo-sures and a 'tripod.

Flash PhotographyFlash photography is necessary fo r

stop-action photography, such aswhen photographing a gear hangingfrom a swaying hoist, halso workswel l for photographing the interior ofa gearbox through the inspection portbecause the light bounces off the inte-rior surfaces of the housing, provid-ing soft lighting. Iuse a Vivatar 283flashgun for photographing compo-nents that are not shiny.Nevertheless, to avoid hot spots.jt

is best to use an extension cord andhold the flash somewhat above and tothe side, at about a 45 angle to thefilm plane. The flash can be mountedon a bracket attached to the camera orheld in one hand. Iind it convenientto hold the flash in my left hand andpress the back of my wri t against myleft temple, while holding the camerawith my right hand. This maintains aconsistent flash-to-camera distance.When photographing at d os e ra ng e.

this technique works wen: Set the lensfor the distance you want and therequired aperture. Look through theviewfinder and rock back and forthslightly to focus precisely: then trip thehurter just as the subject becomes

sharp. For components that are shiny,such as polished gea r t ee th , it is b es t touse th e ring flash rather than t he f la sh -gun inorder to avoid hot spots.

R in g F la sh . Itmay not be practicalto use a tungsten light in crampedquarters, for photography throughsmall inspection port . or in areas

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where electric power is not available.For these cases .I use a Sunpak ringflash with a battery pack. The ringflash surrounds the lens with light an dproduces soft illumination that avoidsmost "hot spots." The results are not asgood as those achieved with the tung-sten lamp because ring lighting lacksgives "flat" photos.Macrophotogr.aphyFor most cia e-up photography, [

use a macro lens and tungst en lighting.The advantages are: Tungsten lighting reflected from

an umbrellagives soft, dispersed lightthat avoids "hot spots" or bright reflec-tions from shiny gear teeth: Tungsten lighting allows viewing

of the subject through the lens,enabling the photographer to see exact-ly what the photograph will bow;

Ma c r o p h o t o g r a p h yis a v er y e f f ,e c t i v etool l or f a i l l u r e

a n a ll y s is .. Adjusting the angle of the light,

camera or subject allows the photog-rapher to get just the right amount ofshadow or highlights to enhance thefeatures he or she wants to show.

] use a Lowe) Tota-Light, 1000 Wrungsten lamp for a light source and aPhotek Goodliter Stowaway umbrella.The light and umbrella are mounted ona Photoflex Litestand . .AIlthe lightingequipment was chosen for it s compact-ness. Total weight for tbe lamp,umbrella and stand is only six pounds.

or most of my photographs ofgear teeth, I use the macrolens with-out the extension tube. A 4 x 6 in.print is about twice the real size of theSUbject. There have been everalinstances where the magnification4 6 GeAR TECHNOLOGY

disclosed features that were not notedin visual inspection of the gears,proving that macrophotography is avery effective diagnostic tool for fail-ure analysis.For extreme close-ups, r add the

extension tube to the macrolens. 1reserve the extension tube for onlythose features of the subject that areespecially interesting because itreduces the working distance andreduces the amount of light reachingthe film. With less light, larger lensaperture are required, and there isIe depth of field.The major problems associated

with macrophotography are: Working distances are small; Depth of field is shallow; Sharp focus is difficult to achieve.Films for MacropbotograpbyFor color slides, ~ use Kodak.

Ektachrome 320T professional film.Itis balanced for tungsten light,elim-mating the need for a lens filter. If adaylight-balanced film is used intungsten light, a No. 80A filter mustbe added to the camera lens to keepthe pictures from being too orange.The disadvantages of using a No.80A filter are that it: Requires two stops of exposure

compensation, giving less depth offield for the same shutter speed; Gives a dim, blue image in the

viewfinder; Gives the photographer one more

thing to remember when changingfilms or light sources;.Causes loss of image quality; Does not reproduce colors aswell as a film originally balanced for

tungsten UghtUnfortunately, I have not found' a

tungsten-balanced film for color prints,o I normally use daylight-balancedFujicolor Reala with a No. 80A filter,

ExposureI use the camera's through-the-lens

(ITL) meter and a gray card to get theproper exposure. For macrophotogra-phy with the tungsten light, a No. 80

A filter and Fujicolor Reala (ISo. 100)film, the exposure is usually aboutfill with a shutter peed of one sec-ond. When using Kodak Ektachrome320T slide film without the No. 80Afilter, the exposure is usually aboutf/16 and 114 second.Ialways bracket the exposure to

ensure that] get at least one goodphotograph of each subject. For colorprint film, I bracket the ba e exposureby one stop. For example, if the baseaperture is fIll, I also shoot the sub-jectat f/]6 and f/8. Because colorslide film is more ensiti ve to theaperture setting, I bracket by 112stop.

Documentationl start every roll of film by pho-

tographing a color card. I write thefilm mil number and the date on thecolor card. This permits me to identi-fy any exposed roll of film becausethe first frame is the color card withthe roll number and date. When thefilm is processed, I ask the photo lab-oratory to include a print of the colorcard. By comparing the actual colorcard to the laboratory's print of thecolor card, the laboratory can correctthe processing so that it produces thecorrect colors.I record each photograph 011 a log

sheet and include a brief descriptionof the subject and the aperture setting,shutter peed, type of film and light-ing. The log sheet. helps to identify thebest camera setting for future pho-tographs and correlates the pho-tographs with my separate, writtendescription of gear failures.It is a good idea to type a list of

instructions for each photographicprocess when first beginning to do fail-ure analysis photography. Put theinstructions on a laminated card andkeep it in your camera bag for quickreference. Itis also a good idea to makea list of all your camera equipment andput it 01 1 a laminated card. When pack-ing up your equipment at the end of theday, checking the list will avoid leavingequipment behind .