Gear-driven dual filter disks of graduated density vary linearly with respect to rotation, allowing a wide range of photographic pyrometry. this technique is applicable in metallurgy, glass, plastics and refractory research, and crystallography

Exton, R. J.

Siviter, J. H., Jr.

Strass, H. K.

English

NASA Technical Reports Server

Filter 1
Camera Lens 
2 
April 1965
	 Brief 65-10100 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Rotating Filters Permit Wide Range of Optical Pyrometry 
Filter 1 
ALIGNMENT OF FILTER AND LENS 
The problem: The present practice of photographic 
pyrometry is confined to a rather narrow range of 
temperatures per camera in use, due to the limited 
capability of current photographic emulsions to re-
produce the brightness contrast of an object as it is 
heated. To determine surface temperatures of an 
object where the temperature variation is more than 
a few hundred degrees F, current practice is to use 
several lenses on a single camera, each with a different 
exposure setting. In an application involving tempera-
ture variation of several thousand degrees F, this tech-
nique becomes impractical because of the prohibitive 
number of lenses required.
The solution: A high-speed motion picture camera 
(single-lens system) with gear-driven dual filter disks 
interposed between the camera lens and the heated 
object. The filters are of graduated density to vary 
linearly with respect to rotation, thus affording, in 
conjunction with camera speed, the equivalent of 
many exposure settings. 
How it's done: Each filter disk is linearly variable 
in optical density in a circular direction about the 
center, with radial ray from center to rim constant 
in density. An initial ray has a transmission density 
of zero and each succeeding ray around the disk a 
greater density according to a linear gradient until a 
(continued overleal) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained its
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19650000099 2020-03-11T17:22:04+00:00Z
terminal ray of maximum density, immediately 
adjacent to the initial ray, is reached. The two 
disks are identical but are so mounted that their 
density gradients are opposite in sign. In their starting 
position, the boundaries marking the abrupt transition 
from zero to maximum density of the two disks are 
aligned as shown above. The camera lens lies in a 
plane between the centers and rims of the filter 
disks which have conventional gear teeth on their rims 
and are driven in opposing rotation by the gear 
arrangement shown in the drawing. A lens shield 
protects against interference from extraneous light. 
These gears are driven by the camera film transport 
mechanism in such a relationship that one complete 
revolution of the filter disks takes place for each 18 
frames of film exposed. Due to the range in exposure 
between the zero and maximum density portions of 
the disks passing before the lens, at least one of the 
18 frames will be exposed properly and will be useful 
for surface temperature calculation. 
Notes: 
I. With the filter rotation to camera speed ratio 
outlined, a complete time-temperature history has 
been made over a range of 18000 to 4500° F. 
2. The graduated-density filter disks used are com-
mercially available.
3. This system of pyrometry can be used to record 
gray body temperatures over a very wide range 
with accuracies better than 2-1/2,, permits tem-
perature gradient and time history measurements 
over extended surfaces, and is relatively insensitive 
to surface emissivity changes. 
4. This technique should find application in the fields 
of metallurgy, crystal growing, glass research, plas-
tics, and refractory research. 
5. This innovation is further described in "Motion 
Picture Camera for Optical Pyrometry" by H. K. 
Strass, U. S. Patent No. 3,041,924 dated July 3, 
1962. Inquiries may also he directed to: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia, 23365 
Reference: B65-10100 
Patent status: NASA encourages the commercial 
use of this invention. It has been patented by NASA 
(U.S. Patent No. 3,041,924), and royalty-free license 
rights will be granted for its commercial development. 
Inquiries about obtaining a license should be ad-
dressed to NASA, Code AGP, Washington, D.C., 
20546.
Source: H. K. Strass, J. H. Siviter, Jr., 
and R. J. Exton
(Langley-33) 
Brief 65-10100	 Category No. 02


Rotating filters permit wide range of optical pyrometry

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