ASTM C1652/C1652M-06
(Test Method)Standard Test Method for Measuring Optical Distortion in Flat Glass Products Using Digital Photography of Grids
Standard Test Method for Measuring Optical Distortion in Flat Glass Products Using Digital Photography of Grids
SIGNIFICANCE AND USE
This test provides accurate data for evaluation of the optical properties of the glass being inspected.
The procedure described is useful for measuring the roll wave introduced during the tempering process of flat architectural glass. (1)
5.3 This test method is also useful for inspection of laminated and tempered automotive glass in transmitted light, in both flat and curved geometries.
SCOPE
1.1 This test method covers the determination of optical distortion of heat-strengthened and fully tempered architectural glass substrates which have been processed in a heat controlled continuous or oscillating conveyance oven. See Specifications C 1036 and C 1048 for discussion of the characteristics of glass so processed. In this test method the reflected image of processed glass is photographed and the photographic image analyzed to quantify the distortion due to surface waviness. The test method is also useful to quantify optical distortion observed in transmitted light in laminated glass assemblies.
1.2 The values stated in either SI units or inch-pound units are regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.3 There is no known ISO equivalent to this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C1652/C1652M − 06
StandardTest Method for
Measuring Optical Distortion in Flat Glass Products Using
Digital Photography of Grids
This standard is issued under the fixed designation C1652/C1652M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Transmitted and reflected distortion in annealed, heat strengthened, and tempered glass can be
measured by several methods.(1,2,7,8,) Qualitative methods are based on the observation of
wavinessintheglassasviewedinofreflectedortransmittedimagesinasetofequidistantlines,called
Zebra Lines. Quantitative measuring techniques are based on several methods, some of which are:
1) Measuring local curvature using mechanical radius gages ((1, 6,9)
2) Moire Fringe analysis (3, 4)
3) Double exposure of transmitted grid images (Practice F733)
4) Projection of an array of round dots (5)
5) Dual laser beams (10)
The user should be familiar with techniques that are available so as to select the most suitable after
considering the precision, speed, and test specification requirements.The test method described in this
document uses a digital camera to capture a transmitted or reflected image of a set of equidistant lines.
Changes in the spacing of lines are used to quantifying the distortion.
1. Scope 1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of optical
responsibility of the user of this standard to establish appro-
distortionofheat-strengthenedandfullytemperedarchitectural
priate safety and health practices and determine the applica-
glass substrates which have been processed in a heat controlled
bility of regulatory limitations prior to use.
continuous or oscillating conveyance oven. See Specifications
C1036 and C1048 for discussion of the characteristics of glass
2. Referenced Documents
so processed. In this test method the reflected image of
2.1 ASTM Standards:
processed glass is photographed and the photographic image
C162 Terminology of Glass and Glass Products
analyzed to quantify the distortion due to surface waviness.
C1036 Specification for Flat Glass
The test method is also useful to quantify optical distortion
C1048 Specification for Heat-Strengthened and Fully Tem-
observed in transmitted light in laminated glass assemblies.
pered Flat Glass
1.2 The values stated in either SI units or inch-pound units
F733 Practice for Optical Distortion and Deviation ofTrans-
are regarded separately as standard. The values stated in each
parent Parts Using the Double-Exposure Method
system may not be exact equivalents; therefore, each system
shall be used independently of the other. Combining values
3. Terminology
from the two systems may result in nonconformance with the
3.1 See Terminology C162 Terminology of Glass and Glass
standard.
Products
1.3 There is no known ISO equivalent to this standard.
3.2 Definitions:
3.2.1 focal length, F—The focal length of a specular
reflector,duetothecurvatureatapointequalsR/2.(See3.2.3.)
This test method is under the jurisdiction of ASTM Committee C14 on Glass
and Glass Products and is the direct responsibility of Subcommittee C14.11 on
Optical Properties.
Current edition approved Oct. 1, 2006. Published November 2006. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/C1652_C1652M-06. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1652/C1652M − 06
In
C1652/C1652M − 06
transmitted light, local thickness changes introduce a conver- makes it possible to quantify the lens power or optical
gence or divergence, equivalent to a lens with a focal length F. distortion of each element of the glass surface defined by the
grid.
3.2.2 optical power, D—The optical power due to the
curvature at a point is D = 1/F. The optical power is expressed
4.2 A uniformly spaced set of parallel lines, usually set at
in diopters, (Units 1/m), or as is typical, in millidiopters. The
45° angle to horizontal, may be used instead of a grid. If such
optical power is also used to quantify optical distortion, the
a set of lines is used, the mathematics of calculation will be
deformation of images reflected from flat glass, or transmitted
slightly altered from those expressed in Appendix X1.
by laminated or bent glass, or both.
5. Significance and Use
3.2.3 radius of curvature, R—The local radius of curvature
at a point on the surface, in meters. R and R are respectively
x y
5.1 This test provides accurate data for evaluation of the
measured in planes x (usually horizontal) and y (usually
optical properties of the glass being inspected.
vertical)
5.2 The procedure described is useful for measuring the roll
3.2.4 roll wave—A repetitive, wave-like departure from
wave introduced during the tempering process of flat architec-
flatness in otherwise flat glass that results from heat-treating
tural glass. (1)
the glass in a horizontal conveyance system. Roll wave
5.3 This test method is also useful for inspection of
excludes edge effects such as edge kink, and distortion induced
laminated and tempered automotive glass in transmitted light,
by assembly or installation.
in both flat and curved geometries.
4. Summary of Test Method
6. Apparatus
4.1 This test procedure was designed to provide an accurate
method of quantifying the optical distortion of glass as it is
6.1 The items shown in Fig. 1 are required to practice this
revealed in reflected or transmitted images. The optical distor- test method:
tion in reflected light can be related to a surface waviness,
6.2 An accurately printed flat screen containing a pattern of
known as roll wave in tempered glass products, or, in trans-
equidistant black lines on a white background.
mitted light, related to curvature and local thickness variations
NOTE 1—The ruled area of the screen should have at least twice the
in laminated glass products. The test method is based on the
dimensions of the area on the glass to be examined.
use of a digital camera which is used to record the appearance
of an accurately printed grid pattern which has been reflected 6.2.1 The line spacing or pitch p (center to center or
from or transmitted though apiece glass. Mathematical analy- corresponding edge to corresponding edge distance between
ses performed on computer of the changes in the grid pattern adjacentlines)definesthespatialresolutionofthesystem.A50
along with the laws of optics and the geometrical arrangement mm [2 in] pitch in both horizontal and vertical directions
FIG. 1 Test Configurations of Reflective Analysis
C1652/C1652M − 06
provides satisfactory resolution for the examination of tem- 8. Calibration and Standardization
pered glass in reflection mode. A smaller pitch can be used
8.1 System calibration is a two-step procedure.
when examination of smaller deformations in laminated glass
8.2 Verification of System Zero
iscarriedoutusingthistestmethod.Thewidthoftheblackline
8.2.1 Set the camera at a distance 2L from the screen.
is typically 6 mm [ ⁄4 in]. The line-to-line distance must be
Capture the image of the screen without a glass panel in place
uniform, in both horizontal and vertical directions. The unifor-
and process the image through the analysis software. The
mity of the line-to-line spacing, p, is critical, because the
image analysis should indicate small values of D throughout
systeminterpretsanon-uniformspacingasopticaldistortion.A
the inspection area, typically less than 5 mdpt.
uniformity of the pitch of 0.2 mm [0.008 in] is satisfactory in
reflective measurements.
8.3 Verification of Calibration (Span Calibration)
8.3.1 This system calibration is determined by the screen
6.3 A digital camera equipped with an a planar lens and an
uniformity and distance, L, to the camera as shown in Fig. 1,
image pixel resolution compatible with the software require-
Fig. 2, and Fig. 3.
ments. These requirements are met by most commercially
8.3.2 Place a panel with known distortion in the test
available digital cameras.
position. Record the screen image and process it through the
6.4 Acomputer using an operating system compatible with
software. The calculated distortion should not differ from the
the software and any peripherals needed to satisfy the data
known value by more than 5 mdpt.
logging and reporting requirements.
8.3.3 The known value of distortion should be established
usingtraceable,curvaturemeasuringmethods.Duallaserbeam
6.5 A software program capable of performing the evalua-
and interferometry are suitable for this purpose.
tion of changes in line-spacing, p, and computation of the
optical distortion, D, throughout the inspected region.
9. Procedure
6.6 Lighting sufficient to provide photographic contrast.
9.1 Set up the grid screen:
6.6.1 Auniform illumination of the screen must be ensured.
9.1.1 Ruled screen board should be vertical, in an upright
In average lighting conditions, four Quartz-Halogen flood-
position.
lamps, 500 watt each, are satisfactory.
9.1.2 When used in reflective mode, the board should have
6.6.2 In a brightly illuminated area, two times higher
a hole, sufficient for viewing through with a digital camera, cut
illumination power is needed to assure good photographic
in its center.
contrast.
9.1.3 When the screen is wall-mounted, so that viewing
through a hole in its center is not possible, the camera can be
7. Sampling
mounted next to the screen or above it. In this configuration
7.1 The number of specimens and frequency of testing is to (see Fig. 2), a V-shaped line drawn from the center of the glass
be determined by the user. to the center of the screen (L ), and from the center of the glass
FIG. 2 Test Configuration for Off-Set Camera
C1652/C1652M − 06
FIG. 3 Test Configuration in Transmitted Light
to the center of the camera lens (L ) represents a geometric, 9.5.5 Add an identification number for the glass by printing
specular reflection. The screen must be perpendicular to the with a felt marker on an erasable board just above or below the
bisector of line L and L and the camera back must be sample
...
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