ASTM D881-90

Test Method for Deviation of Line of Sight Through Transparent Plastics (Withdrawn 1995)

General Information

• Status: Withdrawn
• Withdrawal Date: 14-Jul-1995
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.40 - Optical Properties

Standards Content (Sample)

AMERICAN SOCIETY FOR TESTING AND MATERIALS
#/b Designation: D 881 - 90
1916 RICI SI., Philadelphia. Fa. 1S1W
Reprinted from lha Annual Book d ACTM Standards Capyf~IW ACTM
II not lisled in lhe curmnl combined indu, rmi wir in iha fwl &ilion.
Standard Test Method for
Deviation of Line of Sight Through Transparent Plastics'
This standard is issued under the fixed designation D 881; 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 theyear of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 6. Apparatus
6.1 Telescope, rigidly mounted, equipped with cross hairs
1.1 This test method describes a procedure for measuring,
be sufficiently free of parallax so
by means of a telescope and a target, the deviation of the line (Note i). The telescope shall
of sight through flat or curved sections made of transparent that when the eye of the observer is shifted, the corre-
plastics. sponding movement of the image of the target relative to the
1.2 The values stated in minutes (?r/10800 rad) units are cross hairs shall not exceed one tenth of the smallest scale
to be regarded as the standard, division of the target. The magnifying power of the telescope
1.3 This standard does not purport to address the safety shall be adequate to permit accurate reading of the position
problems associated with its use. It is the responsibility of the of the cross hairs on the target. The mounting of the
user of this standard to establish appropriate safety and telescope shall be such that it cannot be displaced readily
health practices and determine the applicability of regulatory after being clamped in position. To obtain clear images
limitations prior to use. through some specimens, it may be necessary to stop down
the objective of the telescope (Note 2).
2. Referenced Document
NOTE 1-An engineer's transit is a very suitable instrument for
measuring deviations of line of sight.
2.1 ASTM Standard:
NOTE 2-The intended use of the article or material under test may
D618 Methods of Conditioning Plastics and Electrical
determine the size of stop to be used. Thus, if the user will look through
Insulating Materials for Testing
the material with his unaided eye, then the diameter of the stop should
D 883 Definitions of Terms Relating to Plastics*
approximate that of the pupil of the eye. Larger apertures make for
increase of brightness of the image, but frequently the definition is
3. Terminology poorer and the measuremenfs are more difficult or more fatiguing.
3.1 Definitions-Definitions of terms applying to this test 6.2 Target, suitable The shall be so
method appear in Definitions D 883.
made and the illumination shall be such that the divisions
shall be clearly visible when viewed through the telescope
4. Significance and Use
(Note 3). Where deviation in one direction only is of interest,
4.1 This is a functional test for sheets or formed articles,
the target may consist of parallel straight lines; otherwise the
such as certain aircraft windshields and enclosures, the
most convenient form consists of concentric circles.
manner of use of which requires information about the
NOTE 3-Lines ruled in black on a white background, which may be
deviation of the line of sight. The property measured is
either opaque with front lighting or translucent with back lighting, make
determined jointly by the prismatic power of the'pfastic at
the most suitable target for most purposes. The spacings of the lines can
each point and by the angle made with the surface at that
be calculated by a formula as follows:
point by the line of sight. Thus the measurement should be
s = 11~13440
considered as a specialized procedure capable of excellent
where:
precision and reproducibility but not applicable for deter-
s = spacing of the lines, in.
mining optical distortions nor for defining optical quality in
0 = angular deviation, min, corresponding to an apparent shift of the
cross hairs from one cross line to the next line, and
any general sense.
L = distance of the target from that part of the test specimen which is
under examination, in.
5. Summary of Test Method
Thus, if the distance of specimen to target is 40 ft, and if an apparent
shift of the cross hairs from oneline to the next is to correspond to one
5.1 A line of sight is established by focusing a telescope on
minute of angular deviation by the specimen, the spacing of the lines
a target. By placing the specimen to be tested in the line of
will be:
sight, the apparent position of the cross hairs on the target is
shifted. From the magnitude of the shift and the distance
s = (L X 40 x 12)/3440 = 0.140 in.
between the target and the specimen, the angular deviation
6.3 Support for Specimen-A suitable fixture for support
of the line of sight by
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