A system for use in Schlieren photography includes (1) a viewing screen adjacently related to a large grating; (2) a small grating disposed in spaced relation with the large grating; (3) a transparent retainer for confining a transparent medium between the gratings; and (4) optics for imaging the small grating on the large grating. A light source and optically aligned lens are used to project a beam of light along axes extending through the small grating and strike the large grating, subsequent to passing through the medium. A Schlieren image of striations resulting from distortions of light rays proposed by the medium are formed on the screen. A camera is used to photograph the Schlieren image projected on the large screen

Parthasarathy, S. P.

English

NASA Technical Reports Server

United States Patent [19] 
Parthasarathy 
Ull 4,139,291 
[45] Feb. 13, 1979 
SYSTEM AND METHOD FOR OBTAINING 
WIDE SCREEN SCHLIEREN 
PHOTOGRAPHS 
Inventors: Robert A. Froseh, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Shakkottai P. 
Parthasmathy, Burbank, Calif. 
Appl. No.: 876,441 
Filed: Feb. 9,1978 
Int. C l . 2  ........................ C03B 29/00, G02B 5/30; 
HOlJ 3/14 
U.S. c1. ................................. 354/77; 250/237 G, 
356/129 
Field of Search ................... 250/237 G; 356/107, 
356/129; 35V44.77; 354/77 
References Cited 
U.S. PATENT DOCUMENTS 
OTHER PUBLICATIONS 
Nov. 1949, Journal of the Optical Society of America, 
Jan. 1950, The Review of Scientific Instruments, vol. 
1965, Journal of Scientific Instruments, vol. 42, pps. 
May 1963, Scientific American, MoirC Patterns, pp. 
V O ~ .  39, NO. I I ,  pp. 907-908. 
21, NO. 1, pp. 3-6. 
607-610. 
53-62. 
Primary Examiner-Donald A. Griffin 
Attorney. Agent, or Firm-Monte F. Mott; John R. 
Manning; Wilfred Grifka 
[571 ABSTRACT 
A system for use in Schlieren photography including a 
large grating, a viewing screen adjacently related to the 
large grating, a small grating disposed in spaced relation 
with the large grating, a transparent retainer for confin- 
ing a transparent medium between the gratings, and 
optics for imaging the small grating on the large grating 
including a light source and optically aligned lens for 
projecting a beam of light along axes extending through 
the small grating and striking the large grating, subse- 
quent to passing through the medium for thus forming 
on the screen a Schlieren image of striations resulting 
from distortions of light rays produced by the medium, 
2,541.437 2/1951 Prescott ............................... 356/129 
2,636,415 4/1953 Zobel ................................... 356/107 and a for photographing the image 
2,977,847 4/1961 Meyer-Arendt ................. 356/129 X 
2,805,599 911957 Pajeo ................................ 356/129 x projected on the large screen. 
3,897,136 7/1975 Bryngdahl ................... 250/237 G X 8 Claims, 3 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19790012685 2020-03-20T18:28:50+00:00Z
U.S. Patent Feb. 13, 1979 4,139,29 
FIG.  2 
22 
\ 20, 
-- 
F I G .  3 
4,139,29 1 
1 
SYSTEM AND METHOD FOR OBTAINING WIDE 
SCREEN SCHLIEREN PHOTOGRAPHS 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
BACKGROUND OF THE INVENTION 
5 
(72 Stat. 435; 42 U.S.C. 2457). 10 
1. Field of the Invention: 
The invention generally relates to Schlieren photog- 
raphy and more particularly to a system and method for 15 
obtaining wide screen Schlieren photographs. 
2. Description of the Prior Art 
As discussed by Ralph A. Burton, Journal of the Opti- 
cal Society of America, Volume 39, No. 11, November 
1949, Schlieren systems of the conventional type gener- 20 
ally possess the following limitations: 
(1) the area of field is limited to the area of the lens or 
(2) any striation between the light source and the 
mirror used to focus the light, 
knife edge employed appears on the screen along 25 
with those being studied, and 
(3) the light source must approximate a point source. 
Consequently, as also pointed out by Burton, a large 
lens, especially free from striations and correspondingly 
expensive, is required for large areas of field, and the 30 
choice of light source is sharply restricted. 
The author of the paper aforementioned, in an effort 
to overcome the noted limitations without sacrificing 
sensitivity, such as occurs in the use of shadowgraphic 
methods, proposes the use of a method wherein a nega- 35 
tive grid is rididly mounted in a camera for photograph- 
ing striations illuminated by light propagated through a 
positive grid. 
While such a method may satisfy the requirements of 
exoedmental work. it readilv should be aooarent that 40 
such a method and/or the system employed in perform- 
ing the method, simply does not lend itself to practical 
application because of the requirements that a special- 
ized camera be constructed to include therein a negative 
grid. 
It should therefore be apparent that there currently 
exists a need for a practical and economic system 
through a use of which it is possible to obtain a wide 
screen Schlieren photograph of fields of view substan- 
tially unlimited in size employing simple and economic 
photographic equipment and techniques. Therefore, it is 
the general purpose of the instant invention to provide 
an improved system and method for obtaining wide 
screen Schlieren photographs without sacrificing de- 
sired resolution. 
OBJECTS AND SUMMARY OF THE 
INVENTION 
It is, therefore, an object of the instant invention to 
provide an improved system for obtaining wide screen 
Schlieren photographs. 
It is another object to provide an improved method 
for obtaining wide screen Schlieren photographs. 
It is another object to provide in a system for obtain- 
ing wide screen Schlieren photographs the improve- 
ment including optics for imaging a small grating on a 
large grating with a viewing screen adjacently related 
to the large screen whereby matter positioned between 
45 
50 
55 
60 
65 
rg L 
the projection lens and the large grating may be exam- 
ined by examining photographed striations imaged on 
the screen and resulting from distortions of light rays 
projected through the medium. 
Another object is to provide an improved method for 
obtaining Schlieren photographs which is particularly 
useful in connection with still photography, although 
not necessarily restricted in use thereto since the system 
and method may be equally useful when employed in 
connection with motion photography and/or optical 
viewing. 
These and other objects and advantages are achieved 
through the use of a system which includes a projection 
lens for projecting a small grating on a large grating 
with a medium to be analyzed being at least partially 
confined between the projection lens and the large grat- 
ing, and a viewing screen disposed in close proximity 
with the large grating whereby light passing through 
the medium is refracted from its normal course so that 
on arriving at the large grating refracted light is passed 
through the large grating for producing photographi- 
cally reproduceable images of striae on the screen, as 
will become more readily apparent by reference to the 
following description and claims in light of the accom- 
panying drawing. 
DESCRIPTION OF THE DRAWING 
FIG. 1 is a diagrammatic view depicting a system 
which embodies the principles of the instant invention. 
FIG. 2 is a top plan view of the system. 
FIG. 3 is a top plan view of a modified form of the 
system. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring now to the drawing with more particular- 
ity wherein like reference characters designate like or 
corresponding parts throughout the several views, 
there is diagrammatically illustrated in FIG. 1 an im- 
proved system which embodies the principles of the 
instant invention. 
As shown in FIG. I, the system, generally designated 
10, includes a point source of light, designated 12. The 
source preferably comprises an arc light from which is 
propagated a beam of substantially high-intensity hav- 
ing an axis projected through a small grating 14. As a 
practical matter the small grating 14, as currently em- 
ployed, comprises a standard two inch by two inch one 
thousand lines per inch grating. 
Interposed between the small grating 14 and the light 
source 12 there is interposed a condensing lens system 
16 the purpose of which is to direct the beam of light as 
a converging cone through the grating 14. Axially 
spaced along the optic axis of the condensing lens sys- 
tem 16 there is a large grating 18 fabricated in any suit- 
able manner. As currently employed, the grating 18 
includes a pair of horizontally extended steel rods, not 
shown, arranged in vertically spaced parallelism. As 
currently employed, the rods are characterized by a 
diameter of one-half inch spaced forty inches apart. 
Black nylon twine approximately 0.050 inches in diame- 
ter is passed back and forth between the rods and are 
uniformly spaced to provide twenty threads per inch 
along the rods. Thus the large grating is of a relatively 
simple and economic construction. 
Interposed along the axis of the optic axis of the lens 
system 16, between the small grating 14 and the large 
grating 18, there is a projection lens system 20. This lens 
4.139.29 1 
3 
system Serves to project a magnified image of the small 
grating on the large grating. 
Interposed between the projection lens system 20 and 
the large grating 18 there is disposed a retainer, identi- 
fied by the reference numeral 22, FIG. 3, the purpose of 
which is to confine, at least in part, a medium to be 
photographed employing the system 10. As shown, the 
retainer comprises a tubular body formed of transparent 
material, such as a synthetic resin, into which a fluid 
medium is introduced. It will be appreciated that the 
particular retainer is dictated by the nature of the mate- 
rial being subjected to an examination and/or analysis, 
and, where so desired, comprises a tubular body for 
confining a flowing stream of the medium. 
As shown in FIG. 2, immediately adjacent the large 
grating 18, in optic alignment with the lens system 20, 
there is provided a viewing screen 24 the purpose of 
which is to accommodate a display of images of striae 
produced by incident light refracted by the medium 
being examined and passed through the grating 18. 
Preferably, the screen includes a Scotchlight surface for 
enhancing reflection of incident light. In order to pho- 
tograph the image projected onto the screen 24, by the 
lens 20, a conventional camera 26 is located at a suitable 
distance from the grating and focused thereon for pur- 
poses of photographically recording the images. 
In order to enhance the sensitivity of the system a 
Fresnel lens 28 is provided, as illustrated in FIG. 3 in 
lieu of the viewing screen 24. A very low-cost Fresnel 
lens system including multiple elements separately fo- 
cused may be employed. Where the Fresnel lens i s  used, 
the camera 26 is so positioned that the lens thereof is in 
optical alignment with the system 10. Moreover, since 
the Fresnel lens need not be a single element a relatively 
inexpensive Fresnel system can be employed without 
sacrificing resolution. 
It is important to understand that because the retainer 
22 is positioned between the lens 20 and the grating 18 
4 
the rays thereof no longer fall on the threads of the 
grating 18 but instead pass therethrough to strike the 
surface of the viewing screen 24, or Fresnel lens 28, as 
the case may be, for thus providing a Schlieren image of 
5 the refracting medium. The images thus formed are 
then photographed employing the camera 26. 
In view of the foregoing, it should readily be appar- 
ent that the system which embodies the principles of the 
instant invention comprises a low cost system capable 
10 of obtaining wide screen Schlieren photographs em- 
ploying conventional cameras and techniques. 
What I claim is: 
1. In a system for obtaining wide screen Schlieren 
A. means defining a small grating including a plural- 
B. a large grating; 
C. means for imaging said small grating on said large 
grating including a source of light and a condens- 
ing lens for projecting a beam of light along an 
optic axis extended through said small grating, and 
projection lens aligned along said axis in spaced 
relation with the small grating for projecting a 
magnified image of said small grating on said large 
D. a viewing screen adjacently related to said large 
grating, whereby striae produced in the medium is 
imaged. 
2. The improvement of claim 1 further comprising 
30 means for positioning material to be examined between 
said projection lens and said large grating. 
3. The improvement of claim 1 further comprising 
means for photographing images projected on said 
4. The improvement of claim 3 wherein the viewing 
photographs, the improvement comprising: 
l 5  
ity of bars arranged in coplanar parallelism; 
2o 
25 grating; and 
35 screen. 
Screen comprises a Fresnel lens. 
5. The improvement of claim 4 further comprising 
there is no particular limit as to the size of the large camera means disposed in axially spaced relation with 
grating 18. Consequently, Schlieren photographs lim- 40 said viewing Screen for PhotograPhing images Pro- 
ited to a size only by practical matters such as the inten- jected on said screen. 
sity of the light source employed and the sensitivity of 6. The improvement of claim 3 wherein said viewing 
the camera and its lens are obtainable. screen comprises a light reflective surface. 
7. The improvement of claim 6 wherein said means 
OPERATION 45 for photographing images projected on said screen in- 
It is believed that in view of the foregoing descrip- cludes a camera having an optic axis angularly related 
tion, the operation of the device will readily be under- to the plane of said reflective surface. 
stood and it will be briefly reviewed at this point. 8. A method for obtaining wide screen Schlieren 
Employing the system illustrated in FIGS. 1 and 2 a photographs, the steps comprising: 
fluid to be analyzed is deposited in the retainer 22. 50 A. directing a beam of light along a path extended 
Where desired, the medium may be delivered into ambi- from a source through a small grating to a projec- 
ent atmosphere. In any event, a beam of light propor- tion lens and thence to a large grating for thus 
tional from the source 12 is focused by light from the projecting a magnified image of the small grating 
condensing lens system 16, through the grating 14, on on the large grating; 
the projection lens 20. The beam, of course, is broken 55 B. positioning material to be examined between said 
into multiple components by the grating 14 and is re- projection !ens and said large grating; and 
fracted as it is projected by the lens system 20 through C. photographing the image projected on said large 
the medium. The light of the components of the beam is grating. 
refracted from its normal course, by the medium, so that I * * * *  
60 
65 


System and method for obtaining wide screen Schlieren photographs

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