ASTM F733-90(1997)e1

e1
Designation: F 733 – 90 (Reapproved 1997)
Standard Practice for
Optical Distortion and Deviation of Transparent Parts Using
the Double-Exposure Method
This standard is issued under the fixed designation F 733; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Keywords were added editorially in November 1997.
1. Scope 4. Significance and Use
1.1 This photographic practice determines the optical dis- 4.1 Transparent parts, such as aircraft windshields and
tortion and deviation of a line of sight through a simple windows, can be inspected using this practice, and the amount
transparent part, such as a commercial aircraft windshield or a of optical distortion or deviation can be measured. The
cabin window. This practice applies to essentially flat or nearly measurement can be checked for acceptability against the
flat parts and may not be suitable for highly curved materials. specification for the part. The photograph (print or negative)
1.2 This standard does not purport to address the safety can be maintained as a permanent record of the optical quality
concerns associated with its use. It is the responsibility of the of the part.
user of this standard to establish appropriate safety and health
5. Apparatus
practices and determine the applicability of regulatory limita-
tions prior to use. 5.1 Test Room—The test room must be large enough to
properly locate the required testing equipment.
2. Terminology
5.1.1 Method A requires a room approximately 12 m (40 ft)
2.1 Definitions: long.
2.1.1 deviation—the displacement of a line or object when 5.1.2 Method B requires a room approximately 7 m (23 ft)
viewed through the transparent part. Expressed as the angular long.
measurement of the displaced line, for example, milliradians of 5.1.3 The walls, ceiling, and floor shall have low reflec-
angle. tance. A flat black paint or coating is preferred.
2.1.2 distortion—the rate of change of deviation resulting 5.2 Grid Board—The grid board provides a defined pattern
from an irregularity in a transparent part. against which the transparent part is examined. Grid boards are
2.1.3 Expressed as the angular bending of the light ray per of the following types.
unit of length of the part, for example, milliradians per 5.2.1 Type 1—The grid board is composed of white strings
centimetre. held taut, each spaced at a specific interval, with the strings
2.1.4 May also be expressed as the slope of the angle of stretched vertically and horizontally. The grid board frame and
localized grid line bending, for example, 1 in 5 (see Fig. 1). background shall have a flat black finish to reduce light
2.1.5 installed angle—the part attitude as installed in the reflection. A bank of fluorescent lights at each side provides
aircraft. Defined by the angle from a horizontal line to the illumination of the strings.
vertical plane of the part, and the angle of sweep back from a 5.2.2 Type 2—The grid board is a transparent sheet having
horizontal line normal to the center line of the aircraft. See Fig. an opaque, flat black outer surface except for the grid lines. The
2 for an example. grid lines are left transparent, and when lighted from behind
with fluorescent lights, provide a bright grid pattern with
3. Summary of Practice
excellent photographic characteristics.
3.1 The transparent part is placed a given distance from a 5.2.3 Type 3—The grid board is a rigid sheet of material
grid line pattern. A camera is placed so as to photograph the
which has a grid pattern printed on the front surface. Details of
grid pattern as viewed through the part. The photograph is then the grid lines, pattern, and lighting shall be as specified by the
examined and optical distortion or deviation is measured.
procuring activity.
5.2.4 The grid board shall have a width and height large
enough so that the area of the part to be photographed can be
This practice is under the jurisdiction of ASTM Committee F-7 on Aerospace
superimposed within the perimeter of the grid board. Details of
and Aircraft and is the direct responsibility of Subcommittee F07.08 on Transparent
the grid square size shall be as specified by the procuring
Enclosures and Materials.
activity, but grids shall not have a line spacing less than 1.27
Current edition approved May 25, 1990. Published August 1990. Originally
published as F 733 – 81. Last previous edition F 733 – 81 (1988).
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 733
FIG. 1 Optical Distortion Represented by Tangent
cm ( ⁄2 in.), or more than 2.54 cm (1 in.).
TABLE 1 Optical Inspection Distances
5.3 Camera—Unless otherwise specified, the camera shall
Method A
utilizea4by 5-in. film size. The lens opening used shall be f 8
Camera-to-grid-board dis- 1000 cm (32 ft 10 in.)
tance
or smaller. The camera shall be firmly mounted to prevent any
Camera-to-part distance 550 cm (18 ft 1 in.)
movement during the photographic exposure.
Part-to-grid board distance 450 cm (14 ft 9 in.)
Method B
6. Test Specimen
Camera-to-grid-board dis- 450 cm (14 ft 9 in.)
tance
6.1 The part to be checked shall be cleaned, using any
Camera-to-part distance 150 cm (4 ft 11 in.)
acceptable procedure, to remove any foreign material that
Part-to-grid-board distance 300 cm (9 ft 10 in.)
might cause localized optimal distortion. No special condition-
ing, other than cleaning, is required. The part shall be at
7.2.2 The distances for positioning of camera, part, and grid
ambient temperature.
board shall be in accordance with Method A or Method B as
7. Procedure
shown in Table 1. A depiction of the set up is shown in Fig. 2.
7.1 The procuring activity shall specify whether Method A 7.2.3 Prepare a single exposure photograph of the grid board
or Method B (see Table 1) shall be used to measure optical viewed through the part. The camera shall focus on the grid
distortion and deviation. When the part is flat and mounted board.
nearly vertical, Method A is a more stringent test than Method
7.3 Photogr
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