TECHNICAL PROPOSAL FOR A RAPID ALIGNMENT DEVICE FOR MICROSTEREOSCOPE

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A001400010038-6
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 27
• Document Creation Date: December 28, 2016
• Document Release Date: January 12, 2005
• Sequence Number: 38
• Content Type: REQ

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Declass Review by NGA.
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TECHNICAL PROPOSAL
for a
RAPID ALIGNMENT DEVICE
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Page ii
FOREWORD
The following is submitted by the
S'T`AT
STAT
in response to a
Request for Proposal for a Rapid
Alignment Device for Microstereoscopes.
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1W
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Page ii i i
Section Page
2.0 BASIC CONFIGURATION . . . . . . . . . . . . 2-1
2.1 Monocular Device . . . . . . . . . . . . . . 2-1
2.2 Binocular Device . . . . . . . . . . . . . . 2--4
3.0 OPTICAL CONSIDERATIONS . . . . . . . . . . .
3.1 Path Lengths and Apertures . . . . . . . . .
3.2 Pupils and Eyerelief . . . . . . . . . . . .
3.3 Focus . . . . . . . . . . . . . . . . . . .
3.4 Optical Design . . . . . . . . . . . . . . .
3-1
3-1
3-2
3-2
3-3
4.0 MECHANICAL DESIGN . . . . . . . . . . . . . 4-1
4.1 Interpupillary Interface Compensation . . . 4-2
4.1.1 Monocular Configuration . . . . . . . . . . 4-2
4.1.2 Binocular Configuration . . . . . . . . . . 4-2
Appendix Optical Parts List . . . . . . . . . . . A-1
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Page i,i
Figure
Page
1 MonoRAD, External Configuration. . . . . . . .
2-1A
2 MonoRAD, Schematic Optical Diagram . . . . . .
2-1B
3 BinoRAD, External Configuration . . . . . . .
2-4A
4 BinoRAD, Schematic Optical Diagram . . . . . .
2-4B
5 Simplified Optical Schematic . . . . . . . . .
3-3A
6 Monocular Interface Mechanism
4-2A
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1.0 INTRODUCTION
I
For sometime, Microstereoscopes have been in general use by
the photo interpreter which allow detailed viewing of stereo
imagery at relatively high magnification. More recently, these
instruments have been complemented by attachments which permit
partial rectification of either or both input photographs in
order to permit stereo viewing of image pairs which are not
inherently aligned, e.g., with different perspective. These
attachments use variable anamorphic magnification. to match the
geometry of unequal pairs of photographs so that the image may
be fused by the operator's eyes. Experience with these anamorphic
devices has shown that, in practice, the alignment procedure re-
quired to obtain stereoscopic fusion, is difficult and causes
considerable eyestrain to the operator when the disparity of
the two images is excessive.
In the following, two devices are described which alleviate
this problem by superimposing both images from the left and
right section of the stereoscope. One configuration of the
devsee
rapid alignmentA(RAD) terminates in one eyepiece (monocular
RAD), while the second version permits binocular viewing of
the superimposed imagery. By means of this device, the operator
may view the image without eyestrain until complete match is
achieved. After quick removal of the RAD, perfect fusion of the
imagery is then possible.
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2.0 BASIC CONFIGURATION
eyepieces.
ILLEGIB
mirror (beamsplitter) at an equal optical distance from the left
as well as the right image plane, combines the imagery in two
directions. One optical path contains the reflected image from
one channel and, superimposed, the transmitted image from the
second channel. The second path combines the transmitted image
of the first channel with the reflected image of the second
channel. Only one of these optical paths is used in the monocular
version, while both paths are utilized in the binocular device. ILLEGIB
The relayed image in both cases is then observed through regular
The requirement of superimposing the image from both sections
of a stereoscope implies the removal of the regular eyepieces
and relaying the final aerial image plane of the stereoscope
to a new position. Along this optical path, a half silvered
and parallel eyepiece tubes on the microstereoscope, and the
requirement that the images remain erect and non-rotated.' In
addition, there are the practical considerations of weight and
size.
The proposed rapid alignment device is very simple and straight-
forward and oses a mechanical configur~ tion problem rather than
,014, oft ,L G3' +4P Ceiivdar4r`G./ ali e AS-a%- -.!'*C 1?.r
one of optics. This mechanical complexity is a because of the
necessary accommodation to various interpup:illary distances, tiiLGIB
2.1 Monocular Device (MonoRAD)
The technical solution which is proposed for the MonoRAD is
shown in Fig. 1 and 2. Fig. 1 is the external configuration
of a monocular RAD. It consists of two sections which rotate
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 4bome %NOW amia W WO Mrra1 0000 "NO iris am" 6600
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Figure 1 MonoRAD, External Configuration
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.~ ~,..~ age 2-1C
MonoRAD - Top View
,FOCUS
LOCK
I
3
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about the optical axis of the exit eyepiece tube to accommodate
interpupillary adjustment. This method of adjustment is borrowed
from a design used successfully on some binocular microscopes.
The two protruding input sections contain image erecting prisms
and tiltable adapters, which are inserted into the eyepiece tubes
of the microstereoscope (or the anamorphic adapters) in place of
the regular eyepieces.
Figure 2 is an isometric optical diagram (not to scale) which
shows the optical configuration. To relay, erect, and superimpose
the two images, four reflections are necessary for the left channel
and six reflections (including one on the beamsplitter) for the
right channel. Since four reflections are the theoretical minimum
for a prism erector system, the total light loss in the proposed
instrument will be minimized.
Following the left channel optical path from below, the light
passes through a field lens and is reflected on a first surface
mirror outwards (to the left). The eyepiece adapter tubes (in
which the field lens is located) are tiltable about a horizontal
axis at the mirror surface to accommodate their insertion into
stereomicroscopes with inclined eyepiece tubes IStereozoom
70). A mechanism rotates the mirror through half the tilt angle
of the input tubes so that the optical axis is always reflected
into a direction perpendicular to the entrance face of the
following image erector prism. In this prism, the optical path
is reflected about 110 degrees on each of the two surfaces.
Following this, the light passes through the relay lens which is
located exactly at the optical center between input image plane
and exit image plane for unity magnification, and is further
reflected 900 up into the eyepiece tube. Passing through a beam
splitter tube, and another field lens, the final image is then
formed at the back focal plane position of the eyepiece.
25X1
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The optical path for the right channel is similar and equivalent
except that the relay ler is located physically in a different
position. In order to mintain equal optical path in glass on
both sides, the addition 4l a,3. reflection between image erector prism
and relay lens in the rift channel, will be either on a mirror
surface, or, if a prism 3s used, an equivalent block of glass
must be cemented onto the image erector prism of the left channel.
The images of both channels are combined on the beam splitter
which is mounted in the right-hand assembly and moves with it.
Only half of the combined image is used; the reflected image
of the left channel and the transmitted image of the right
channel is not needed and is absorbed within the housing.
The mechanical configuration of the MonoRAD is such that the
eyepoint of the new eyepiece is located about 3 inches above
and about 2.5 - 3 inches behind the position of the eyepoint of
the original instrument. This places the center of gravity
over the instrument so that there is no danger of the micro-
stereoscope tipping due to the added weight of the RAD.
It should be pointed out that the input eyepiece tubes tilt
in a vertical plane with their axes of rotation being parallel
only if the interpupillary distance is adjusted to 65 mm (mid-
range). If the instrument is set to other distances, the axes
of the input tubes are still coplanar, but with different in-
clination. The effect is that the output eyepiece tube will
tilt slightly from the original direction, as interpupillary
adjustments are changed. This, of course, applies only to
stereoscopes with inclined eyepieces. On the High Power Stereo-
viewer, with parallel eyepiece tubes, the monocular viewing tube
will be colinear with the original direction.
eye?rft.
/ 414;11r_
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2.2 Binocular Device ($inoRAD)
ILLEGIB
fore, since'the exit an entrance axis of the in'stru ent are
!parallel, the final image will not be rotated.
The optical configuration of the device is shown schematical y
The binocular RAD is shown sc;ematically in Figures 3 and 4.
Figure 3 shows the external configuration. The two major
assemblies interlace and rotate with respect to each other
about a vertical axis. This, in turn, moves the four eyepiece
tubes in an.arc for interpupillary distance adjustment. The
use of the device on microstereoscopes with inclined eyepiece
tubes is made possible by rotating the input tubes about an
axis which is colinear with the optical axis in the instrument
after the first 900 reflection. This method is convenient and
is used in some periscopes to scan objects in various directions,
but causes the optical image to rotate. In order to derotate
the image, the exit eyepiece tubes will be n)echanically connected
to the input tubes and will tilt thrpu the same angle. There-
ij hardly larger than that of the monocular version.
by observing the basic considerations on aperture sizes and pat
,lengths discussed in Section 3.1, the overall size of the BinoRAD
ii Figure 4. The image combining beam splitter is again located
at the same optical distance from both input image planes and
iii addition is symmetrical about input image and output image
p~anes. The optical path is reflected through a series of prisms ILLEGIB
wlpich erect the image and avoid physical interference of the two
a$semblies. The number of reflections necessary to do this is
eight for the left channel and ten for the right channel. The
optical path length and, of course, the total weight of the
device is increased compared to the monocular version. However
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Figure 3 BinoRAD, External Configuration
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4 57
 LEFT
CHANNEL
FIELD
LENS
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FIELD LENS
I~
Figure 4 BinoRAD, Schematic Optical Diagram
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RIGHT
CHANNEL
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The eyepieces themselves tilt about axes which are never parallel.
Therefore, if the instrument is used on stereomicroscopes with
inclined eyepieces, the main body of the BinoRAD will be tilted
with respect to the image plane. The tilt will be towards the
horizontal which will improve the appearance of the combined
microstereoscope -- anamorphic adapter-- rapid alignment device.
The number of reflections between the input field lens and
relay lens, and between relay lens and output field lens is
different in the left and the right channel. Therefore, one
reflection in each path of the right-hand assembly should be
on a first surface mirror, or compensation for the additional
glass must be provided in the left channel. Because of weight
considerations, it may be necessary to utilize mirror systems
rather than prisms in the BinoRAD, even at the expense of lower
light efficiency. A careful size and weight analysis will be
performed in order to arrive at the best solution.
Optical considerations which apply to the MonoRAD as well as
to the BinoRAD are discussed in the next section. A tentative
list of optical elements needed for the devices is included
in the Appendix.
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3.0 OPTICAL CONSIDERATION
Practical considerations of size and weight, commensurate
with this type of equipment, dictates that the total optical
path through the instrument be kept as short as possible.
These considerations have led to the configuration of the
monocular and binocular version as previously described.
The optical path length at each bend in the optical path is
dependent upon the aperture for the imaging bundle at that
position. For this reason, all prisms in the instrument
will be dimensioned to be no larger than that required at
that particular position. The entrance and exit aperture
must be large enough, however, to pass the full field
(approximately 20 mm) of the original instrument. This
determines not only the minimum size for all prisms, but
also the clear apertures and focal lengths for field and
relay lenses.
The necessary bends in the optical path may be accomplished
by reflections on first surface mirrors or by total reflection
in glass prisms (as shown in Figure 2 and 4). The use of
glass prisms has the advantage that the optical path becomes
shorter than the physical distance between elements which
permits smaller apertures for the relay lenses, and smaller
dimensions for some prisms. Another advantage is that
assembly of the instrument is simplified since part of the
alignment accuracy is inherent in the prism angles, particularly
when compact pre-cemented prism assemblies with more than one
reflecting surface are used. Light losses in totally
reflecting prisms are also less than the light losses on
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first surface mirrors. The primary argument against exclusive
use of prisms is their weight, which, in this particular
application, is an important consideration.
It is a requisite that not only the image at unity magnification
must be relayed to the final position in the exit eyepiece
tubes, but that the pupils of the original microstereoscopes
must be relayed correctly, as well. Microscope eyepieces
are designed for a 240 mm tube length, which is standard in
modern instruments. The exit pupil of the eyepiece, which
is actually the real image of the objective pupil, is located
at a specific distance from the eyepiece. This distance is
called the eyerelief. It is important to optically design
the RAD such that the eyerelief is maintained. This is
achieved by the combination of two field lenses. The first
field lens forms an image of the instrument pupil at the
location of the relay lenses. The second field lens creates
a virtual image of this pupil at the correct optical distance
of 240 mm from the exit tube. In order to avoid light
losses, and to maintain the numerical aperture of the
microscope, this dimensioning of pupils must be done for the
lowest magnification of the primary stereomicroscope.
In order to compensate for differences in refractive power
of the operator's eyes, binocular microscopes have one
focusable eyepiece. Binocular zoom microscopes, on the
other hand, have both eyepieces (actually the eyepiece tubes)
focusable since the image planes must remain in a fixed
position in order to maintain the parfocal property throughout
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the zoom range. Because of the possible differences in
the operator's eyes, the eyepiece tubes on which the RAD
is to be mounted, may be at unequal height. Therefore, at
least one of the input tubes of the RAD, which replace
the regular microscope eyepieces, must be focusable in
order to compensate for this condition. Unfortunately, the
relative position of the parfocal image plane inside the
eyepiece tubes, is not identical for all microstereoscopes.
This is dependent upon the location of the back focal plane
of the eyepiece, which varies with the particular optical
and mechanical design of eyepieces. It is, therefore,
suggested that both input tubes for the RAD should be focusable.
Since the internal dimensions of the RAD will not change,
the relay lenses need not be focusable. The image plane
will then be relayed to a fixed, standard position within
the output eyepiece tubes. One of these tubes must also be
focusable, however, in order to accommodate differences in
the operator's eyepower. On the monocular version, the single
eyepiece tube must be focusable.
3.4 OPTICAL DESIGN
Figure 5 shows a simplified, straight line optical schematic
of the RAD, ignoring the glass prisms in the optical path.
In the optical design of the instrument, it will be assumed
that the input image is perfectly flat and aberration free.
Input and output field lens will be outside the respective
image planes so that any dust on their surfaces will be out
of focus. As mentioned before, not only will the image be
relayed at unity magnification, but the pupils must be relayed
correctly as well. Since these conditions are unique to
this particular instrument, commercially available optics
cannot be used. The optical design, however, is relatively
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RELAY LENSES r-- OUTPUT FIELD LENS
INPUT FIELD LENS f=120mm f"=240mm
f ^-80mm 12mm dia N ~{ 20mm dia
BEAM SPLITTER ! OUTPUT. IMAGE PLANE
Figure 5 Simplified Optical Schematic
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simple. Since the system is almost symmetrical, the field
lenses can be piano convex single elements. The relay lens
consists of two achromatic doublets or one (Hastings)
triplet. In the case of the binocular version, two doublets
will be used with the beam splitter in collimated light.
The optical design, as well as the performance analysis,
will be done with an available automatic lens design program
ACCOS) designed for the IBM 360 Computer.
The lenses and prisms will be made by one of several qualified
vendors which specialize in the fabrication of precise
optical elements to specification.
In order to phrserve contrast in the relayed image, design
practices commensurate with this type of equipment will be
rigorously observed. For example, all non-reflecting and
non-transmitting surfaces on prisms will be ground and inked
black and all tubing, etc., is oversize and black anodized
to avoid glare. Baffles or aperture stops will limit the
light bundle passing through the instrument to only the
required aperture in accordance with general practices of
high quality instrument construction.
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4.0 MECHANICAL DESIGN
Both binocular and monocular optic assemblies would be housed
in 356 aluminum alloy castings to attain maximum rigidity
with minimal weight and the fewest number of machined components.
A quick disconnect to interface with the anamorphic lenses
utilizing the split barrel technique, would provide maximum
bearing area and least deflection. Focus adjustments would
be made by conventional microscope mechanism.
Both configurations are free to rotate about a bearing along
the vertical axis of the beam splitter, to give the required
operator interpupillary distance. Rotational resistance is
built into this bearing using wave springs and friction material
washers for correct operator "feel".
Focusing adjustment where required is made by rotating knurled
rings which translate the appropriate lenses, via fine screw
threads.
Adapter removal via a quick disconnect is implemented by
depressing a lever which unclamps a split barrel that fits
on to the anamorphic eyepiece.
The castings and all mechanical components will be black anodized
or painted optical black. The weight of the monocular adapter
will be approximately 5 lbs. and the weight of the binocular
adapter will be 7 lbs.
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1
4.1 INTERPUPILLARY INTERFACE COMPENSATION
In order to compensate for interpupillary adjustments at the
adapted interface, it is necessary to incorporate a self-
adjusting mechanism to obtain the correct optical reflective
angle at the first mirror after the interface.
4.1.1 Monocular Configuration
a mirror via a two-to-one gear reduction; thus maintaining the
correct reflective angle, irrespective of the anamorphic
interpupillary distance. Refer to Figure 6.
bearing rotates, it turns an integral spur gear that drives'
/~
n re se c e ning through a wiper action.' A}s-the spier ica
self-aligning along the axis of the anamorphic lenses. The
b rin s are entrapped. within the adapteO housing
spherical
The adapter barrels terminate in spherical bearings which are
4.1.2 Binocular Configuration
arrangement utilizing two similar spur gears and an idler
gear suffices for this compensation.
by rotation of the eyepieces through a similar angle. A simple
The adapter barrels for the BinoRAD are free to rotate about
one axis to compensate for interpupillary adjustment at the
interface. In this case, however, image rotation is prevented ILLEGIB
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Number
Required
LIST OF OPTICAL PARTS (MonoRAD)
Description
Input field lenses,plano convex,
f 120 mm, dia 22 mm, CA 20 mm
Relay lenses, Achromatic triplet,
f 60 mm, CA 12 mm
Output field lens,plano convex,
f = 240 mm, dia 22 mm, CA 20 mm
Input mirrors, 20 x 30 CA x 3 mm
Prisms,(220? deviation by two reflections),
entrance faces 18 mm
90? prisms, faces 18 mm
Mirror, 15 x 22 CA x 3 mm
Beam splitter cube, at least 40% reflection,
40% transmission, 3 outside surfaces polished,
20 mm cube
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Number
Required
LIST OF OPTICAL PARTS (BinoRAD)
Description
90? prisms, 20 mm faces
Periscope (90-90) prisms, 20 mm faces
Periscope (90-90) prisms, 16 mm faces
90? prisms, 15 mm faces
U-bend prisms, 15 mm faces
Beam splitter cube, 14 mm,
4 outside faces polished
Input field lenses
Output field lenses
Relay lenses, achromatic doublets,
14 mm CA
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