Frontispiece. Underwater panoramic photograph, 380 by 1200

GOMER T. McNEIL*

Photogrammetry, Inc.Rockville, Maryland

A Wide-Field, Underwater,Panoramic CameraHaving an angular field of 38° by 120° and a focallength of 3.42 inches for photography at 85 inches,the lens resolves 50 lines per millimeterat the center with an aperture of f/2.4. ,

(Abstract on next page)

INTRODUCTION

SEVE TY YEARS AGO, Louis Boutan pro­duced the first underwater photograph at

the Arago marine laboratory in France. Thestrange world beneath the oceans has re­ceived much publicity in recent years for ac­celerated explorations and scientific investiga­tions. An increased utilization of the oceanas a source of food and minerals will be man­datory for future generations. Many scientifictools will be devised to support the great un­derwater search. Qualitative and quantita­tive photography will continue to serve effec­tively underwater as it has served so pro­ductively on land and in the air. Underwaterphotography will be used to a greater degreefor oceanographic, engineering, biological,and military projects.

Many severe problems need to be over­come in the underwater environment. Turbid-

* Presented at the Annual Convention of TheAmerican Society of Photogrammetry in Washing­ton, D. C. in March, 1963.

37

ity, light absorption, and light scattering ofthe water appear to be insurmountable prob­lems. However, science and engineering have

GOMER T. McNEIL

38 PHOTOGRAMMETRIC E GINEERING

teamed up in the past and have solved prob­lems that have seemed to be unsolvable.Many components of the underwater systemwill require much improvement or a totallydifferent device. The purpose of the Under­water Panoramic Camera is to produce highquality, wide-angle photography of under­water scenes as a serious attempt to improvethe recording component.

Practically all underwater photography isexposed from a conventional camera that is

angle lens is required to coyer more area ofthe object at a closer distance.

TECHNICAL DESCRIPTION

Figure 1 illustrates the basic geometricaloptics of a conventional camera in combina­tion with a plane-parallel window. Light raysemanating from the object pass through thewater and are refracted at the water-glassinterface and again at the glass-air interfaceand impinge on the objective lens of the

ABSTRACT: Quality wide-field coverage is produced by projecting high-resolu­tion imagery through a relatively small angular slit and mechanically extendingthe field to a wide coverage by rotating the objective lens. A non-circular cylindri­cal image surface is utilized for optimum focus of a planar object surface. Someof the specifications for the lens are: a field of 38° by 120°; f=3.42 inches;50 lines per mm at f. 2.4 at the center; object dt:stance of 85 inches; shutter speed1/250 second; shutter slit 0.085 inch; and pan time 0.3 second.

placed in an underwater housing with either asimple plane-parallel window or a moreelaborate optical window.

A review of the conditions encountered inpractice conclude the following criteria:

.. Short Object Distance. Due to turbidity,light absorption, and light scattering,the object distance should be as short aspractical, especially with t e use of colorfilm.

.. Fixed Focus. As there is usually a rela­tive motion between the photographerand object, it is a very difficult operationto use a range-finder for the focusing ofan underwater camera.

.. Short Image Distance. The (ocal lengthor the image distance in this case, shallbe as short as practical as the camera isfixed-focus and it is desirabl to obtainas large a depth of field as possible .

.. Wide Angle. The requirement of main­taining a short object distance results inreduced linear dimensions of the objectplane.

A review of the technical literature,whether it be styled for the amateur or theprofessional, repeatedly emphasizes the re­quirement for wide-field coverage sinceturbidity, light absorption, and light scatter­ing require the photographer to move closerto the object being photographed. A wide-

camera. From the viewpoint of the lens, therays appear to be coming from an apparentobject that is equal in size to the actual ob­ject but is located at j of the distance to theactual object. The camera, therefore, must be

FIG. 1. Conventional camera behind a planewindow.

A WIDE-FIELD, UNDERWATER, PANORAMIC CAMERA 39

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FIG. 2. Conventional camera behind correctingwindow (Aquar-I vanoA' lens).

focused at ~ of the distance to the actual ob­ject. This distance condition naturally ex­tends the angular field of view from ~ 8 in ob­ject space to 8 in image space. The factor ~ isthe reciprocal (approximately) of the index ofrefraction of water. This theory is valid forrelatively small values of 8.

Plane windows introduce significantamounts of coma and lateral chromatic aber­rations. The full-field in water is limited toapproximately 30° for a plane window and aresolution of approximately 20 lines per mm. l

It is of academic interest to point out thatthe maximum theoretical full-field of a planewindow is approximately 98° owing to thecritical angle of the glass-air interface.

Figure 2 is an optical schematic of an im­proved and more elegant window designedby A. Ivanoff of the Museum of NaturalHistory, Paris, France2• The use of theAquar­Ivanoff lens permits the conventional camerato be focused for the actual object distanceand retains the same angular field in wateras in air. This correcting window covers amuch larger angular field with greatly re­duced aberrations compared with a planewindow.

The simplest means of producing qualitywide-field coverage is to project high-resolu­lution imagery through a relatively smallangular slit and mechanically extend thefiRld to a wide coverage through rotation ofthe objective lens. This technique of rotatingthe lens has been used to produce high qual­ity photography from panoramic cameras

with an object space of air. Obviously, thesame approach can be exploited for a camerawith an object space of water. The exploita­tion is even greater in an underwater envi­ronment as a wide-angle water lens is far morecomplex to design and manufacture than awide-angle air lens.

I n has been established previously in atechnical paper3 that the front and rear nodalpoints must fall on the axis of rotation to pre­clude image movement for all object dis­tances. This principle was utilized in the de­sign of the NavScan Hi and Lo PanoramicCameras for the U. S. Navy. The apparentpositions of the front and rear nodal pointswere made to fall on the axis of rotation bythe proper positioning of reflecting surfaces.The design approach to the UnderwaterPanoramic Camera is an in-line optical sys­tem in place of a folded optical system. Thein-line system is preferred since it is simpleand more compact. However, the in-line sys­tem does not have reflecting surfaces toplace the nodal points on the axis of rotation.

A very simple solution to preclude imagemovement at a finite object distance is de­rived from Figure 3 as follows:

A is the object point,a is the image point,D is the object distance,d is the image distance,N 1 is the front nodal point,N 2 is the rear nodal point,o is the axis of rotation of lens.

t10N1A is similar to t10N2a, since object rayANI is parallel to image ray N 2a. It can thenbe stated that:

E I EI+DE 2 = E, +d •

EIE, + Eld = E,E2 + E,D,

E,d = E 2 D,

E I D- = -. (1)E, d

Formula 1 simply means that if the ratioof the eccentricities of the front and rearnodal points is made equal to the ratio of theobject to image distances, no image move­ment will occur for objects at a distance D.

Formula 1 can also be derived fromFormula 7 presented in the previouslymentioned technical paper.3

IJEdc=-+IJE,. (2)

D

Substituting the image distance d for thefocal length f in Formula 2 to accommodate

40 PHO OGRAMMETRIC ENGINEERING

.,?----~~--------~IR--t-----J)

rFIG. 3. Geometry of a rotating lens to preclude image movement at a finite object distance.

where

d = the image distance,D, = the diameter of stationary gear,D. = the diameter of sprocket,D 3 = the diameter of sprocket gear.

in the opposite direction to that of the lens­slit-magazine assembly by means of the geartrain consisting of the stationary gear, idlergear, and sprocket gear. Since it is requiredthat 2 7r image distances pass the slit perrevolution, the following relationship mustbe maintained:

(4)

85 inches

87.0 mm. or 3.42 inches

f /2.4 to f /32380 X 1200 in water1/250 second0.085 inch

Image Distance atCenter

Object Distance atCenter

Relative ApertureField AngleShutter SpeedShutter Slit Width

If the conditions of Formula 1 are fulfilled,image movement due to rotation for the givenobject distance D is zero. Formula 3 is alsoused to determine the magnitude of the imagemovement for an object distance other thanD.

The image and object surfaces of a pan­oramic camera focused for a finite object dis­tance are cylindrical in configuration. If op­timum focus of a planar object surface is re­quired; the non-circular cylindrical image sur­face is utilized as shown in Figure 5.

The perspective recorded by an under­water panoramic camera is similar to the per­spective produced by an aerial panoramiccamera. Figure 6 is a perspective (not to scale)of a swimming pool wall faced with squaretile.

The physical characteristics of the Under­water Panoramic Camera shown in Figure 7are:

IJE2 = - IJE,d/D.

The change in algebraic sign is simply accom­plished by positioning the axis of rotationbetween the front and rear nodal points. Su b­stituting in Formula 3:

-IJE,d0= ---+IJE.,D -

the condition other than when the lens is fo­cused at infinity, the general formula takesthe following form:

fJE,dc = -+IJE2• (3)

D

I t can be seen from Formula 3 that c equalszero when

E, D-=-.E 2 d

Figure 4 is a schematic of the lens and filmtransport system of a 3600 under-waterpanoramic camera. 4 The optical window is asection of a concentric glass dome that coversa 3600 horizontal field of view and is an in­tegral component of the lens system. Sincethe axis of rotation of the lens system passesthrough the center of curvature of the con­centric optical window, the lens system isoptically identical for any position of rota­tion throughout the 3600 field of view. Thelens system is designed especially for an ob­ject space of water as contrasted against theconventional approach of utilizing a lens de­signed for an object space of air in combina­tion with a plane or corrected window. Theaxis of rotation is so positioned that the ratioof the front and rear nodal point eccentri­cities is made equal to the ratio of the objectdistance to the image distance. The lens, slit,and magazine assembly are mechanicallytied together. The film is moved past the slit

A WIDE-FIELD, UNDERWATER, PANORAMIC CAMERA 41

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FIG. 4. Schematic diagram of the underwater panoramic camera.

The Underwater Panoramic Camera differs

Pan TimeFormat on 70 mm. FilmFilm CapacityCamera Size

Peak Spectral RangeResolution at Center,

//2.4

0.3 second2i X 7i inches24 exposuresIi! inches dia.X8!

inches high4,500 A to 5,000 A50 lines per millimeter

from the schematic camera depicted inFigure 4 in that the angular field is reducedfrom 3600 to 1200 and the film remains sta­tionary during the time of exposure. Since thenodal separation of the underwater lens is 0.6mm., the rear nodal point is placed on theaxis of rotation. Using a slit width of 1.5°, animage movement of 0.6 micron is computedfrom Formula 3. This magnitude of image

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C/Ii'CUI.I1R' Cf'I./NlJIi'ICAI. IMI/ISE 05VNFI1CE~-"----/FM ClIi'CI./I.I1R' CYLINOIi'ICIiL Oa<lECT GVIlFI/CE

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FIG. 5. Image surface for a planar object surface.

42 PHOTOGRAMMETRIC ENGINEERING

~V .......

i'...,.~- - r---

I----- ---- ""-

-r-- ----r--- -~--....... ,/

FIG. 6. Perspective of a swimming pool wall.

ACKNOWLEDGMENTS

FIG. 7. The Underwater Panoramic Camera.

movement has an insignificant effect on theresolution.

The Frontispiece shows an underwaterphotograph recorded by the UnderwaterPanoramic Camera. The photograph coversa 30 foot length of the swimming pool wallwith the camera about 8t feet from the wall.The fifteen youngsters are performing a walkin water space.

NEW hard coating. Greater depth

of field with Interpupillary

adjustments from 50mm to 75'!'m.

Hundreds of uses. Inspections,

map & aerial photo readings!

Legs fold neatly into pocket

LIGHTWEIGHT.CAST·ALLOY

COATED OPTICS

Grateful acknowledgment is extended tothe N ava! personnel at the Bureau of NavalWeapons, Photography, and the Naval Pho­tographic Center who gave their assistance insupport of the successful completion of theproject. Credit is also reflected to RobertGallipeau, de~igner and fabricator of theseven-element lens specifically computed foran object space of water, and to the em­ployees of Photogrammetry, Inc., whotransformed the concept into a workable in­strument.

REFERENCES

1. Thorndike, E. M. "A Wide-Angle, UnderwaterCamera Lens." Journal of the Optical Society ofAmerica, Vol. 40, 12, December 1950.

2. Ivanoff, A. and Cherney, P. "Correcting Lensesfor Underwater Use." Journal of the SMPTE.Vol. 69, 4, April 1960.

3. McNeil, G. T. "NavScan: A Dual PurposePanoramic Camera." PHOTOGRAMMETRIC ENGI­NEERING, Vol. XXVII, 3, June 1961.

4. Patent No. 3,141,397 dated July 21, 1964,"Underwater 360 0 Panoramic Camera."