A continuing problem in high-speed motion picture photography is adequate lighting and the associated temperature rise. Large temperature rises can damage subject matter and make recording of the desired images impossible. The problem is more severe in macrophotography because of bellows extension and the necessary increase in light. This report covers one approach to reducing the initial temperature rise: the use of filters and heat-absorbing materials. The accompanying figures provide the starting point for selecting distance as a function of light intensity and determining the associated temperature rise. Using these figures will allow the photographer greater freedom in meeting different photographic situations

Slater, H. A.

Walker, E. D.

English

NASA Technical Reports Server

NASA-TM-83620 19840014353
NASA Technical Memorandum 83620
Method of Reducing Temperature in
High-Speed Photography
Ernie D. Walker
Lewis Research Center
Cleveland, Ohio
and
Howard A. Slater
Rochester Institute of Technology
Rochester, New York 14623
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METHOD OF REDUCINGTEMPERATUREIN HIGH-SPEEDPHOTOGRAPHY
Ernie D. Walker
NationalAeronauticsand Space Administration
Lewis ResearchCenter
Cleveland,Ohio 44135
and
Howard A. STarer
RochesterInstituteof Technology
Rochester,New York 14623
INTRODUCIION
A continuingproblem in high-speedmotion picturephotographyis adequate
lightingand the associatedtemperaturerise. Large temperaturerises can
damage subjectmatter and make recordingof the desiredimages impossible. The
problemis more severe in macrophotographybecauseof bellowsextensionand the
necessaryincreasein light. This reportcovers one approachto reducingthe
initialtemperaturerise: the use of filtersand heat-absorbingmaterials.
The accompanyingfiguresprovidethe startingpoint for selectingdistanceas
a functionof light intensityand determiningthe associatedtemperaturerise.
Using these figureswill allow the photographergreaterfreedomin meeting
differentphotographicsituations.
In most hlgh-speedphotographythe film is exhaustedin less than TO sec-
onds, with most work requiringonly 1 to 5 seconds(approxlO0 ft at a frame
rate of 4000 fps is equal to l sec). The major temperaturerise occurs in the
first TO seconds;the temperaturecontinuesto rise at a reducedrate to 30
seconds,where it stabilizes. Therefore,it is criticalto controlor delay
the rate of temperaturerise in the first 5 to lO seconds. Many methods have
been employedto achievethe desired temperaturereduction- water-cooledfil-
ters, vortex generators,etc. This reportdeals only with filtrationusing
uncoatedglass and infrared(IR) absorbing(cutoff)filters.
FILTRATIONMEIHOD
In a laboratoryenvironment,a high-lntensltyGE EHL tungstenbulb (300 W
at 120 V) was mountedon a long aluminumfilter holder that was securedto a
chamberto reduce heat convection,as shown in figure I. The chambercontained
an Iron-constantanthermocouplethat displayedtemperaturethrougha digital
display. A MinoltaAuto III F light meter was used to record incidentlight.
To establisha constant,temperaturedata were taken at a given distance
with no filters in place. Then additionaldata were taken for variousfilters.
In the first 5 secondsthe temperatureincreased33° F above ambientfor the
light sourcewithoutany filters(fig. 2). Since a coated O.125-1nch-thlck
filterwas to be tested,it was necessaryto determinethe effect that O.125-
Inch-thlckuncoatedglass has on temperature, lhe curve in figure 2 for thick
glass shows this temperaturerise. Using a standardof 5 seconds,the curve
shows a temperaturerise of 28° F above ambientas comparedwith the 33° F
Figure1. -Testsetupwithrecommendedfiltration.
constant. This representsa 15 percentreductionin temperaturerise.
ReplacingO.125-1nch-thickglass with an equal amount of thinnerglass (three
sheets,each 0.046?5 in. thick) securedtogetherproduceda 24 percent reduc-
tion in temperaturerise. This extra reductionin temperaturerise with an
equal amount of glass can be attributedto contact resistancebetweenthe sur-
faces of the filters.
Figure 3 representsthe spectral"performance"or responseof the coated
IR cutoff filter. The visible spectrumis from 350 to 700 nanometers,with the
infraredregion fallingbeyond 700 nanometers. The hlgh-lntensltytungsten
bulbs generate extremeheat and almost one-thlrdof it is caused by the longer
IR wavelengths. A single O.125-1nch-thlckIR cutoff filterproduced the
greatest reductionin temperaturerise, 27 percent (fig. 2).
Combiningtwo or more IR cutoff filtersdid not significantlyreduce the
temperaturerise. Conversely,the first IR filter absorbedall IR radiation
while transmittingthe visiblewavelengths. Adding further IR cutoff filters
did not reducethe temperaturerise significantlyas the full transmittanceof
visiblewavelengthscontinued. Combinationsof other filterswere then tested
to obtain greater temperaturerise reductionwith a minimum of light loss.
140
135
130
125
120
I15
_- llO lOO-
_3
105
o_
_ aoo
95
85 A NO FILTER
o THICKGLASS
80 <> IRFILTER _ /
n RECOMMENDED
FILTRATION
15
7o I I I I i i t , _ i l i
0 5 I0 15 20 25 30 %o 400 500 600 700 800 900 I000 II00 1200
TIME,sec SPECTRUM,nm
Figure2.-Temperatureriseasa function Figure3.-SpectralesponseofIRcutoffilter.
oftimeat light-to-subjectdistanceof
6 inchesundera varietyof conditions.
45.0 --
32.0 L _ WITHFILTERS
22.0 --
._ 16.o
11.0
8.0
5.6 I ! I I I6 I0 14 18 22 26
DISTANCE,in.
Figure4.-fnumbersasa functionofdistancewithoutfiltersandwithrecommended
filtration.(fnumbersarebasedon1160thofasecondandASA25film.)
A single IR filter and two O.125-1nch-thlck glass filters each composed
of three thln layers of O.04675-1nch-thlckglass producedthe best overall
temperaturerlse reductionwlth mlnlmumloss of light. After 5 seconds,the
set of filters produced a 45.4 percent temperature rise reduction (fig. 2) and
a light reductionof only 2/3 stop (fig. 4).
3
104
Z_ NO FILTER
I00 0 THICKGLASS
O IRFILTER
[] RECOMMENDEDFILTRATION
%
88 _-_ 92
84 2 88
/-AMBIENT 80
I I I I I I I
126 8 10 12 14 16 18 20 22 24
DISTANCE.in. 16
Figure5. - Temperatureisein 5 secondsasa functionof distancefor recommended I-I
filtration.
z2 ! I ! I I I I
6 8 10 12 14 16 18 20 22 24
DISTANCE,in.
Figure6.-Temperatureisein5secondsasafunctionfdistanceundera
varietyofconditions.
%
92
_ 88
w
a. 84
80
0
pAMBIENT
zz I I I I I I
6 8 I0 12 14 16 18 20 22 24
DISTANCE.in.
FigureI.-Temperaturein15secondsasa functionofdistanceforrecommended
filtration.
The successof the three-flltercombinationbecamemore evidentafter 15
seconds. With no filters In place, a temperatureof 130° F was reached
(fig. 2), 58° F above ambient. The singlethick glass reducedthe temperature
to 125° F, or a poor 8.6 percent reductionin temperaturerise. The single IR
cutoff filter produceda 24.1 percentreduction. Finally,the combinationof
three filters (IR, three thln glass, and three thln glass) produceda 53.4
percentreduction: a temperatureof only 99° F was obtained,as displayedin
figures2 and 5, and again wlth only a 2/3-stoploss of light.
By varyingthe llght-to-subJectdistance,a greatertemperaturerlse re-
ductioncan be obtained(figs. 6 and 7). For example,doubling the distance
to 12 inchesand using the three-flltercombinationresultedIn a minimal 4° F
rise above ambient,as comparedwlth a lO° F rlse without filters(fig. 6).
Therefore,dependingon the photographer'sneeds and requirements,a vast ar-
ray of combinationscan be obtainedby using the accompanyinggraphs.
115 --
LIGHT-TO-SUBJECT ?DISTANCE,
110 in. /
-- O 6
I-I 12
lO5
100
3z
_ 95
2
,,_ 16
8
85 _
80 -- LIGHT-TO-SUBJECT
2 DISTANCE,
in.
o 6
/5 q n 12
1 Z_ 18
<> 24
NOREADING
zo I I I I I I
3O 45 6O 75 9O 105 120 o I I I I I I
VOLTAGE,V _o 40 so 60 zo Bo 9o too 11o 12oVOLTAGE,V
Figure8.-Temperatureafter30secondsas a functionfvoltage Figure9. - fnumberas a functionofvoltagealvariousdislaneesforrecommendedfiltration.
at various distances for recommendedfiltration. (fnumbersarebasedonll60th ofasecondandASA25film.)
Anothermethod of controllingtemperaturerlse In conjunctionwlth the
filters Is to use a voltageregulator. If distance from the light source can-
not vary and only a limitedtemperaturerise can be tolerated,a voltagereg-
ulator in combinationwlth the three-filterset will reduce temperaturerlse
greatly (fig. 8). There wlll be significantlight loss at lower voltagesand
greaterdistances(fig. g).
More light may be needed (to flll shadows,etc.). Figure lO shows the
greater heat producedby two lights (with filters)at a given distance.
Temperatureincreasedapproximately5° to 7° F above the slngle-llght(with
filters)temperatureafter 5 secondsand increasedlO° to 13° F after 15 sec-
onds. One stop was gained when a second lightwlth filterswas added at a 45°
angle.
For example,to obtain hlgh-speeddata of Ice formingon an airfoil, the
temperaturerise could not exceed 3° F above ambient In the first 5 seconds,
and an apertureof f/5.6 would be needed at a frame rate of 200 fps. The fllm
used was Trl-X reversal7278 wlth an ASA of 160. At thls frame rate, a pln
registercamerawith a 120° shuttercould be used with a factor of 3 times the
frame rate. This would make the correspondingshutterspeed equivalentto
1/600thof a second. Figure 6 shows that a distanceof 16 incheswlth ASA 25
fllm at 1/60th of a secondwlll glve an appropriatelow temperaturerise.
Figure 5 shows that an f number of 8.5 at 16 inches can be used wlth one light
and the filter combinationsof IR, three thin glass, and three thln glass.
ConvertingASA 25, which was used In all of the graphs,to ASA 160 requires
approximatelya 2-1/2-stopexposuredecrease. Going from 1/60th of a second
to 1/600threquiresa 3-1/3-stopexposureincreaseto f/6.0. A final example
of using the graphs Is given next.
NUMBEROF
LIGHTS
0 1
r7 2150
A I(WITHFILTER)
<> 2(WITHFILTER}
140
130
120
II0
af
IOO
9o
80
70 I I5 10 15 20 25 30
TIME,sec
Figure10.- Temperatureasa functionoftime
fora varietyof conditions.
The hlgh-speedfilming of pesticidebeing sprayedon cabbageleaves is
required. A leaf temperatureexceedingllO° F changesthe waxy compositionof
the leaf and the way the spray interactswlth it. The depth of field requires
f/8.0 with a frame rate of 4000 fps for good speed resolution. Figure 6 shows
that using a distanceof 6 incheswith the recommendedcombinationof filters
producesa leaf temperatureof only 87° F - far below the limit of llO° F.
Figure 4 shows that at 6 inchesan f number of just under 32 is possible. Now,
this informationmust be convertedto the actual ASA and shutterspeed. Again,
data were collectedat ASA 25 with a shutterspeed of 1/60th of a second. ASA
25 to 400 (7250 High Speed Video News Tungstenfilm) requirea 4-stop decrease
in exposure to f/128. Using a Fastex camerawith a factor of 3 times the frame
rate producesan equivalentshutterspeed of 1/12 000th of a second. Going
from 1/60th to 1/12 O00th of a second requiresan increaseof 7-3/4 stops to
f/ll. This gives the photographerfreedomto have a longer film runningtime,
change the distance of the light or add anotherlight, open up another stop,
etc.
SUMMARY
Clearly,filtrationis an effectivemethod of reducingthe temperature
rise associatedwith hlgh-lntensltytungsten lights. By using an infrared
cutoff filter to eliminateinfraredwavelengths,which produceapproximately
27 percentof the rise in temperature,and combiningit with sheets of thin,
uncoatedglass, a reductionof over 50 percent in temperaturerise is possible
at close distances. Light loss is kept to a minimum - only a 2/3 increase in
exposure is necessarywith the filters in place at most distances. By varying
the llght-to-subjectdistance in conjunctionwlth the filters,temperaturecan
be controlledeven further. The figuresaccompanyingthis paper representa
startingpoint. Figure 2 can be used to approximatethe temperaturerise in a
given time under a varietyof conditions. By using figure 4, a photographer
can approximatethe f/numberand distancecombinationnecessaryfor the photo-
graphicsituation. Figure 8 shows how temperatureis affectedby voltageat
variousdistances_f a voltageregulatoris added. Figure9 illustrateshow a
photographerwill have to compensatefor exposureas voltagevaries. Finally,
figures 5 to 7 will enable the photographerto predicttemperaturerise at
varioustimes and distances. The f_guresoffer a wide selectionof pos-
sibilitiesthat will give the photographermore flexibilityin meetingdif-
ferent photographicsituations.
1. Report No. 2. Government Accession No. 3. Reolpient's Catalog No.
NASATM-83620
4. Title and Subtitle 5. Report Date
March 1984
Method of Reducing Temperature in High-Speed Photo- 6.PerformingOr anizatlonC de
graphy
7. Author(s) 8. Performing Organization Report No.
E-2021
Ernie D. Walker and Howard A. Slater
10. Work Unit No.
9. Performing Organization Name and Address
Nationa I Aeronautics and Space Admini strati on It ContractorGrantNo.
Lewis Research Center
C1evel and, Ohio 44135 13. Type of Report and PeriodCovered
12. Sponsoring Agency Name and Address Technical Memorandum
National Aeronautics and Space Administration 14.SponsoringAgencyCode
Washington, D.C. 20546
15. Supplementary Notes
Ernie D. Walker, Lewis Research Center; Howard A. Slater, Rochester Institute
of Technology, Rochester, New York 14623.
16. Abstract
A continuing problem in high-speed motion picture photography is adequate
lighting and the associated temperature rise. Large temperature rises can
damage subject matter and make recording of the desired images impossible. The
problem is more severe in macrophotography because of bellows extension and the
necessary increase in light. This report covers one approach to reducing the
initial temperature rise: the use of filters and heat-absorbing materials.
The accompanying figures provide the starting point for selecting distance as
a function of light intensity and determining the associated temperature rise.
Using these figures will allow the photographer greater freedom in meetingdifferent photographic situations.
17. Key Words (Suggested by Author(s)) 18. Distribution Statement
Heat; Reduction in photography; Infrared; Unclassified - unlimited
Cutoff filters STARCategory 74
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Unclassified Unclassified
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