TEST AND EVALUATION REPORT (Sanitized) 7X FILAR EYEPIECE SET FOR THE ZOOM(Sanitized) STEREOSCOPE SYSTEM

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04560A007300010020-6
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 21
• Document Creation Date: December 28, 2016
• Document Release Date: March 25, 2003
• Sequence Number: 20
• Publication Date: December 1, 1971
• Content Type: REPORT

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NATIONAL PHOTOGRAPHIC
INTERPRETATION CENTER
TECHNICAL
PUBLICATION
CONFIDENTIAL
TEST AND EVALUATION REPORT
1X FILAR EYEPIECE
SET FOR THE ZOOM
STEREOSCOPE SYSTEM
Declass Review by NIMA / DoD
GROUP I: EXCLUDED FROM
AUTOMATIC DOWNGRADING
AND DECLASSIFICATION
CONFIDENTIAL
NPIC/R-51/71
DECEMBER 1971
25X1
25X1
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WARNING
This document contains information affecting
the national defense of the United States.
within the meaning of Title 18, sections
793 and 794, of the U.S. Code, as amended.
Its transmission or revelation of its contents
to or receipt by an unauthorized person is
prohibited by law.
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TEST AND EVALUATION REPORT
25X1
SET FOR THE ZOOM
1X FILAR EYEPIECE
STEREOSCOPE SYSTEM
25X1
25X1
Test and Evaluation Branch
Engineering Support Division
Technical Services Group
NATIONAL PHOTOGRAPHIC INTERPRETATION CENTER
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ABSTRACT
1. INTRODUCTION
2. SUMMARY OF TEST RESULTS
3. CONCLUSIONS
4. DESCRIPTION OF EQUIPMENT
S. TEST DETAILS
Page
1
5.1 Acceptance Tests 9
5.2 Operational Evaluation 15
5.3 Engineering Analysis and Evaluation 15
Distribution List 17
LIST OF ILLUSTRATIONS
25X1
Figure 1. Zoom
Filar Eyepiece Set iv
Figure 2. Filar Eyepiece Reticle 8
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ABSTRACT
The Filar Eveniece set, designed and fabricated 25X
25X1 Iwas tested according to C
actual requirements and for usefulness to NPIC. The
Filar eyepiece is of good optical design and construction.
However, it will not be useful to NPIC until the mechanical
interfacing problem with the Zoom Stereoscope is 25X1
solved. This stereoscope has both eyepiece focusing rings
and image rotation rings on the eyepiece tubes. The Filar 25X'
Eyepiece holding mechanism is designed to bridge these movable
rings to a stable portion of the eyepiece tubes to prevent
rotation of the Filar Eyepiece. Both IEG and TEB found the
mechanism to be inadequate.
The Filar Eyepiece satisfied sixteen of the other twenty
contractual requirements. The other deficiencies are not very
serious.
Both IEG and IAS evaluated the Filar Eyepiece and made
generally favorable comments about the optical characteristics.
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1.1 Background
The 7X Filar Eyepiece set (Fig. 1) was developed by
25X1 for use on Zoom and modified
25X1 Zoomi Stereoscope systems. It provideste PI with the
capability of obtaining measurements on roll film as a part
of routine photo interpretation. Contract monitoring was
performed by TSG/RED for IEG.
Because of the length of the Filar Eyepieces, the
25X1 Zoom system must be modified with certain internal
design changes. The testing reported here was done only
with the modified versions.
Final delivery of the eyepiece set was made on
24 February 1971. A memorandum test report (TSG/ESD/TEB-
084/71) was issued in April 1971, stating that the eyepieces
generally meet the contract requirements except for an
apparent yellow color seen through them and for certain
potentially serious mechanical problems.
The IEG and IAS operational evaluations were completed
in October and August of 1971. Their comments are included
in Section 5.2.
1.2 Test Objectives
Test plan objectives accomplished include: 1) testing
per twenty-one contractual requirements, 2) operational
evaluation by two components, and 3) minor engineering
evaluation testing.
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2.1 General
The Filar Eyepiece (Figure 1) is a microscope eyepiece,
fitted with a reticle and a movable cross-hair (Figure 2)
which may be adjusted with a calibrated dial. The set
consists of the Filar eyepiece itself and a companion eye-
piece of similar optical characteristics but without the
measurement capabilities.
Testing of this instrument was performed in three
phases: (1) acceptance testing against contractual require-
ments, (2) operational evaluation by experienced PI's, and
(3) engineering evaluation to ascertain certain characteris-
tics not given in the specifications.
Overall thel Filar Eyepiece is of good
optical design and construction, subject to correction of
certain mechanical problems.
2.2 Acceptance Tests
The eyepieces satisfy sixteen of twenty-one contractual
requirements. Of the five deficiencies found in the accep-
tance testing only one was commented on in the operational
testing. The comment was that the holding mechanism which should
restrain the Filar Eyepiece from rotating sometimes slips. The
remaining deficiencies were:
o The eyepieces impart a yellowish tinge to the
image.
o Certain parts requiring non-reflective coatings
are not blackened.
o Greenish and yellowish rings may be observed
within the eyepieces, suggesting improper anti-
reflection coating.
o The operating manual omits needed cautions and
is not up-to-date in some respects.
The design objectives and specifications that were met
include field-of-view, optical magnification, reticle layout,
optical resolution (both on- and off-axis), optical aberr-
ations, filar motion, eye relief, interpupillary settings,
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parfocality (zoom), mechanical (not optical) construction,
compatibility with Zoom Stereoscopes, optical schematic,
and manufacturing drawings.
2.3 Operational Evaluation
IEG found the Filar Eyepiece set suitable for operational
use subject to the following revisions: (1) change the reticle
by lengthening the cross line of the crosshairs and (2) revise
the holding mechanism to lock the eyepiece firmly in place
during measurements.
They singled out the following features for favorable
comment:
o No distracting color.
o Negligible distortion.
o Flatness of the field-of-view.
o Wideness of the field-of-view.
o Optical magnification (7X).
o Torque adjustment on micrometer shaft.
o Location (transverse) of the fixed scale.
25X1
2.4 Engineering Analysis and Evaluation
Possible damage to Zoom internal parts can still
occur with modified Zoom w enever the left (but not
the right) eyepiece focusing adjustment is left all the way
down and the Filar Eyepieces are inserted hurriedly.
No interference occurs in the normal focus range of the
instrument.
To make reasonably accurate measurements the PI must
achieve optimum adjustment of the Filar eyepiece holding
mechanism spring, place very little non-useful pressure on
the micrometer drum, and avoid changing the interpupillary
distance adjustment during a measurement.
which has two separate adjustment features (focus and image
rotation) on each eyepiece tube. The holding mechanism must
therefore bridge two movable parts to a stable part of the
eyepiece tube. The resulting mechanical interface problems
(see Sections 5.3.2 and 5.3.5) are potentially serious. A
mechanical engineer who examined it has doubts about the
suitability and ruggedness of the prototype's holding
mechanism feature.
The Filar Eyepiece has to be mounted on a Zoom
25X
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The 7X Filar Eyepiece is of good optical
design an cons ruc ion. Its mechanical interfacing with
the Zoom is not acceptable to NPIC for procurement
without modification.
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4. DESCRIPTION OF EQU
IPMENT
The 7X Filar Eyepiece set consist
roughly cubical storage case (6 x 6 x
eyepiece fits into th
s of tw
7"). T
o eyepieces in a
he measurin
Zoom
25X1
e left or right e
Stereoscope S
ste
yepiece
tubes of iI
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is the
'
y
ms w
ith o
e
excepti
on
Th
early
fied Z
.
e exception
oom
i
th imag
e rotation 25X
25X1
The measuring (Filar) eyepiece has a flat steel spring
which extends past the image rotation ring to the body of
the eyepiece tube. A knurled thumbscrew holds the spring and
rubber pad against the tube body to prevent rotation of the filar
during a measurement.
Visible through the measuring eyepiece is a fixed reticle
scale and a movable crosshair (Fig. 2). A micrometer drum
both moves the crosshair across the field-of-view and provides
the measurement of the movement. This eyepiece has a focus
adjustment to accommodate different observers. The companion
eyepiece services to provide the same magnification and eye-
point to the other eye since the 7X eye feces are not compatible
with the eyepieces usually used on Zoom
25
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MOVING CROSS-HAIR
Figure 2. Filar Eyepiece Reticle
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DESIGN OBJECTIVES
- SPECIFICATIONS
5.1.1
Field-of-
138/(magnification)
View (mm)
Zoom Setting 0.7X
1.5X
3.OX
Requirement 28.2
(mm)
13.1
6.6
5.1.2
Eyepiece
Magnification
(linear)
5.1.3
Reticle
RED furnished a drawing for
Layout
the reticle (Figure 2).
5.1.4
Optical
Maintain the optical quality
Resolution
of the same instrument when
(On-axis and
used with =10X Wide Field
off-axis)
Eyepieces.
TEST METHOD
Record the visible range
on a stage micrometer at
three equiangular direc-
tions across the field-
of-view.
Visually superimpose a
scale placed on the light
table (viewed with one eye
looking through the Zoom II
and an illuminated, calibrate
circle (viewed at unity magni-
fication through a prism ar-
rangement with the other eye).
Note how many scale divisions
are included within the
calibrated circle.
Visual comparison between
the drawing and the reticle.
Focus at maximum zoom magni-
fication in the center of the
field-of-view. Without re-
focusing position the Zoom
(at minimum zoom magni-
fication) so that the resolu-
tion target is in the appro-
priate part of the field-of-
view and read the sagittal
(radial) and tangential re-
solution values. Divide the
resulting values in line
pairs/mm by the appropriate
magnifications (7X for the lOX
eyepiece and 4.9X for the 7X
RESULTS - CONCLUSION
Zoom Setting 0.7X 1.5X 3.OX
Meas. (min.) 28.9 13.6 6.6
Satisfies requirement.
They appear to be identical.
Meets requirement.
The Filar Eyepiece met this
requirement. The Filar
Compensating Eyepiece was
20% low in one out of ten
measurements. The least
increment of this measurement
due to the discrete (or step)
nature of resolution targets is
about 10%.
25X1
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5.1.5 Apparent
Color
DESIGN OBJECTIVES
- SPECIFICATIONS
TEST METHOD
eyepiece at a 0.7X zoom
setting). Record the
median value of three
observers after computing the
percentage increase in resolu-
tion per magnifying power given
by the filar eyepieces over
the =lOX Wide Field eye-
piece.
Maintain the optical quality of Subjective comparison by two
the same instrument when used test engineers.
with Q Wide Field Eyepieces.
5.1.6 Anti-reflection All refractive elements shall be
Coating coated for maximum light trans-
mission.
5.1.7 Astigmatism
(on-axis)
Visual examination for
anti-reflection coatings.
Maintain the optical quality of Look for any set of
the same instrument when used orthogonal lines which re-
with = Wide Field Eyepieces. quire refocusing to obtain
sharp focus from one line to
the other.
Use the filar measuring
capability to determine the
amount of pincushion or
barrel distortion that is
present.
It essentially meets this
requirement.
They agree that the filar
eyepiece is definitely yellower.
Does not meet the requirement.
A blue cast is observable at
both ends of the eyepiece when
turned in the light like a dia-
mond. However, distinct rings
are visible in the blue cast and
three distinct sets of greenish
and yellowish rings are visible
when looking through the filar
eyepiece.
It may not meet the requirement.
No significant on-axis
astigmatism was observed.
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DESIGN OBJECTIVES
ITEM SPECIFICATIONS
5.1.9 Congruence Image shall not be rotated,
(Object-Image) inverted, or reverted with
respect to the object.
5.1.10 Filar Motion Shall be constructed in a manner
that is physical
the existing 15X
Filar. One revolution o the
micrometer drum shall
advance the filar crosshair
lmm in the eyepiece focal plane.
The drum shall be divided into
100 equal increments. Parallax
between the moving crosshair and
the fixed reticle shall be a mini-
mum.
5.1.12
Exit Pupil
The companion (compensating)
eyepiece shall project an exit
pupil of the same object from
the second optical path of the
Zoom IIto the same plane as
that o t e filar eyepiece.
5.1.13
Interpupillary
Minimum of 60mm with the mea-
Distance
suring scale along the 'X' or
'Y' axis. At about 30? it
should be 66. Smm.
TEST METHOD RESULTS - CONCLUSION
Check
Meets requirement.
Check Meets requirement.
height where the smallest
and sharpest exit pupil
shows on the screen.
Measure the movement It ranged from 18.5 to 21.0mm
required to take a ground for extreme zoom and IPD settings.
glass screen from contact The arithmetic average of 26
with the eyepiece to that readings is 19.7mm.
Focus both eyepieces. Use About lmm.
a ground glass screen to make
the exit pupils visible.
Measure the mismatch in height
from the object plane. Essentially meets requirement.
Suspend a ground glass Except for the maximum focal
screen over the eyepieces so setting (the highest physical
that small sharp exit pupils position) the readings were
are made visible. Measure the 60mm for the 'X' position and
distance between the centers 59.6mm for 'Y', and 65.5mm for
of the exit pupils. the -30? orientation. The
maximum distances were all well
over 80mm.
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DESIGN OBJECTIVES
SPECIFICATIONS TEST METHOD
5.1.14 Constancy Both the object image and the Measure the refocusing
of Focus reticle/scale shall remain in required to maintain sharp
sharp focus throughout the focus as the zoom setting
Zoom zoom range. is varied.
5.1.15 Mechanical All surfaces shall be of a Conduct an external
Construction corrosion-resistant type or inspection and examine the
shall be suitably treated for drawings.
protection against corrosion.
All hardware shall be of Ameri-
can Standard sizes, with a mini-
mum of types of sizes used, and
shall be corrosion-resistant.
Wherever possible, sealed bear-
ings of the prelubricated type
shall be used. All sharp edges
and corners shall be rounded
so as to prevent any injury to
personnel. Structural rigidity
of the device shall be suffi-
cient to withstand repeated
jarring.
RESULTS - CONCLUSION
Except for eyepiece focus
settings of about + 3 diopters
no refocusing was required when
zooming from 3.OX down to 0.7X.
Essentially satisfies this
requirement.
The drawings call for anodizing
or other treatment for all metal-
lic surfaces. The visible hard-
ware is either stainless steel,
chrome-plated, or painted. The
micrometer screw (internal) is
cold finished, C12L14, steel.
12L14 is not a stainless steel,
yet no finish is specified.
However, for our office type
environment it is considered that
there is no real corrosion hazard.
The remainder of this requirement
is met.
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DESIGN OBJECTIVES
SPECIFICATIONS
ITEM (REQUIREMENTS)
5.1.16 Optical All non-reflecting and non-
Construction transmitting internal surfaces
shall be coated with non-
reflecting black material.
Optical elements shall be
mounted with sufficient
rigidity to maintain align-
ment and withstand repeated
jarring.
5.1.17 Physical Must be as compact as possible.
Configuration A lock will be provided to
prevent rotation of the filar
about the optical axis of the
Conduct an external
inspection and examine the
drawings.
Measure the maximum exter-
nal dimensions along the
micrometer drum axis and from
the Zoom mating shoulder
(or seat . heck the lock.
5.1.18 Compatibility The eyepieces will be com- Mount on several appro-
patible with any 53-70-24 priate Zoom=Stereoscope
Zoom Stereoscope (Zoom and Systems.
with the new 53-70-25 Image
Rotation Versions of the
Stereoscope (Zooml lonly.
RESULTS - CONCLUSION
While most of the internal
surfaces requiring black coatings
are so coated,not all of them are.
The remainder of this requirement
is met.
The micrometer drum axis
dimension is 4 1/32". The maxi-
mum height is 3 1/32". The lock
was provided (see paragraphs
5.3.5 and 5.3.6 for engineering
evaluation). In less than 9
months of intermittent use the
locking spring (flat, type 301,
stainless steel) was bent more
than 10? out of shape (Fig. 1).
Questionable.
Two operating components
evaluated the e e ieces on
different Zoom eyepieces
and found no
fault except for t e locking fea-
ture see paragraph 5.2.2(c).
Preacceptance and acceptance test-
ing used still other Zoom
with the same results.
5.1.19 Operation Operation manual will be Study it and apply the
Manual delivered. Gunning Fog Index which gives
the years of formal education
a reader would need to read
it with ease and understand-
ing.
Most features are well de-
scribed. The locking feature
description is not up-to-date.
There is no warning about possible
damage when inserting into the
Zoom =(Seeparagraph 5.3.4)There
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5.1.19 Operational
Manual
(continued)
DESIGN OBJECTIVES
SPECIFICATIONS
(REQUIREMENTS)
is no discussion of measurement
errors that can be introduced
by accidential changes in the
IPD. A sample paragraph had a
fog index of 12.5 years. (8 to
14 is considered good.)
5.1.20 Optical Sche-
An optical schematic will
Drawings 537025-001, 537053-001,
matic
be furnished in lieu of
optical detail drawings.
and 537057-001 satisfy this
requirement.
5.1.21 Drawings Manufacturing drawings will Check About 40 drawings were
be provided for mechanical furnished. They appear to be
parts and assemblies. adequate except for BS3705S-128
which does not correspond to the
part and 311650-127 which is
difficult to read.
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5.2 Operational Evaluation
5.2.1 General
Both IEG and IAS conducted operational evaluations
of the Filar Eyepiece set. They gave their findings to
ESD/TEB for inclusion in this T1E Report. Their comments
included both favorable and unfavorable ones.
5.2.2 Subjective Comments
Below is a collection of comments from the operating
components.'
(a) The magnification (7X) is satisfactory.
(b) There is negligible distortion of the image and
no distracting color is introduced.
(c) The locking screw does not hold the Filar eye-
piece firmly in place. The entire eyepiece
sometimes turns when the micrometer knob is
turned, thus causing an error in the measurement.
Image rotation (on the Zoom frequently
occurs when the Filar eyepiece is turned.
(d) The fixed scale is satisfactory, its location
is good, and its width and density are acceptable.
The cross line (of the movable crosshair) should
be longer to facilitate alignment with long
objects.
(e) The width of the field-of-view and its flatness
are impressive.
(f) The torque adjustment (for the micrometer drum) is
especially good.
5.3 Engineering Analysis and Evaluation
5.3.1 There is no mechanical stop at one end of the micrometer
drum's range. At about 0.17 of a revolution past zero on the
scale the drum begins unscrewing from the filar eyepiece.
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5.3.2 When the interpupillary distance setting of the Zoom
is changed the eyepiece tubes rotate slightly. Since they
contain pechan prisms the images rotate through twice the
angle that the eyepiece tube is rotated. Consequently, the
reticle and imagery rotate unequal amounts.
5.3.3 Changing the orientation of the filar measuring axis
typically changes the image rotation settings. See also
5.2.2 (c).
5.3.4 When the left eyepiece tube focus adjustment of the
Zoomi.s all the way down, the filar eyepieces encounter
1 to 2mm of intereference upon being inserted into that tube.
No interference occurs in the normal focus range of the
instrument.
5.3.5 Three out of five observers had great difficulty main-
taining parallelism when translating the filar crosshair over
a set of parallel lines. The filar eyepiece locking mechanism
requires optimum adjustment because overtightening causes the
metal spring arm to bear against the eyepiece tube which takes
some pressure off of the rubber friction pad. About 25 inch-
ounces is the maximum torque obtainable. The operator's hand
operates the filar micrometer drum at a lever arm distance of
about 2 1/2 inches. Therefore a tangential force of only
10 ounces will override the eyepiece lock under even the best
conditions.
5.3.6 When the filar eyepiece is left on the Zoom for
a long time (from one day to the next) the rubber friction
pad sometimes sticks to the eyepiece tube of the Zoom
Sometimes some of the rubber is left on the Zoom when
the filar eyepiece is removed leaving a rough surface on the
outside of the eyepiece tube.
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