evaluation of an underwater single lens reflex camera equipped with

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EVALUATION OF AN UNDERWATER SINGLE LENS
REFLEX CAMERA EQUIPPED WITH AUTOMATIC
FOCUS, AUTOMATIC EXPOSURE
AND WATER CONTACT OPTICS
Thomas C. Kline, Jr.
Prince William Sound Science Center
P. O. Box 705
Cordova, AK 99574, USA
The first production underwater single lens reflex (8LR) camera, the Nikonos RS,
was introduced to the world at the 1992 DEMA show by Nikon Corporation (Japan). The
initial three water contact lenses designed specifically for it include a close-focusing 28
mm wide angle, a 20 to 35 mm wide angle to normal focal length zoom, and a 50 mm
macro lens that focuses to life size. In 1994, these lenses were supplemented with a 13
mm full-frame fisheye lens. All four lenses have f/2.8 maximum and f/22 minimum
apertures. The camera, lenses and new Nikon 88104 and 88105 strobes have a 100 m
maximum depth rating, an increase from the 50 m of previous Nikonos equipment. The
former underwater strobes, however, are compatible with the RS as are strobes from
other manufacturers (after suitable electronic modification). The RS camera, 20 to 35 mm
and 50 mm lenses and 88104 strobe were tested under a variety of challenging
underwater photographic scenarios. The exposure system consistently produces good
results. All system components, except for an 88104 strobe, have performed without
failure during three years of operation. The automatic focusing works well under most
circumstances. High (e.g. silvery fish) and low contrast situations (e.g. translucent animals)
result in excessive "searching" by the autofocus system. Thus manual focusing is
recommended. The automatic focus functions well for macrophotography during night
dives when a strobe equipped with a modeling light is employed. Recommendations for
improvements include use of a more advanced autofocus sensor and display of frame
number and focus distance in the viewfinder. The superlative aspects of the system are
the viewfinder and optical quality.
Keywords: Nikonos RS; underwater photography
THE NIKONOS CAMERAS
The first amphibious camera, the Calypso-phot co-developed by DeWouters and Cousteau
(Hillebrand and Hauschild 1993) and developed further by Nikon Corporation (formerly Nippon Kogaku,
i.e. Japan Optical) has gone through several model changes under the Nikonos name. These Nikonos
models are essentially box cameras because of their simple direct-vision viewfinders (the camera lens is
not a viewfinder component) (Ray 1979). Lenses for the Nikonos include those designated "UW aI
(underwater) for use in water and not in air, because it is impossible to design lenses to work well in both
environments (Wakimoto 1967). McNeil (1972) defined a water lens as ala lens that is interfaced with an
object space of water and an image space of air. Water contact lenses, the more commonly used
synonym of water lenses, are thus lenses designed specifically for optimal optical performance in water.
II
Many serious underwater photographers have opted to use topside single lens reflex (SLR)
cameras in underwater housings to have viewing of the image produced by the camera lens and groundglass focusing. However by doing so, they have compromised optical quality. These underwater
photographers have desired an amphibious SLR Nikonos camera (e.g., Couet and Green 1989)
combining the functional advantages of these former alternatives. This wish came true when Nikon
unveiled the Nikonos RS-AF (hereafter referred to as the RS) camera at the 1992 Diving Equipment
Manufactures Association show at New Orleans, LA. The optical equipment for the RS consists of water
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Diving for Science... 1995
contact lenses; the RS's water contact lenses are designated nR-UW" for reflex underwater. The RS
targets the specialist markets which includes scientific diving and is examined here in that context.
After years of anticipation, underwater photographers now have the supreme optical quality of
water contact lenses in combination with an SLR camera. The quantum leap from box camera with water
contact lenses (Nikonos I to V) to the Nikonos RS has also caused a concomitant leap in cost (Wu 1994).
The relative low cost of the Nikonos V reflects the age of the design, because the camera has been in
production for a decade. The V's technological level is comparable to step-focusing manual advance 35
mm cameras that cost -$100. The RS should be compared to cameras such as the Nikon F4 or N8008S. A
friend in the industry (Jim Larsen, Dolphin Too Inc., pers. comm.) told me that an underwater SLR would
cost $4,000 in 1987. This is the cost of the RS with a 28 mm lens in 1995 which can be attributed to
autofocus technology. If Nikon presented an underwater SLR 10 to 20 years ago, it would have been a
manual focus camera. The reward for our wait has been the incorporation of autofocus technology in the
original Nikonos SLR design. I think the autofocus technology has actually curbed the cost by eliminating
the need for mechanical linkages. The elimination of knobs on the lenses (except for the zooming knob
on the 20 to 35 mm lens) should also greatly enhance their reliability.
Mortensen (1940) listed the following as the significant parts of any camera:
1. An enclosed dark space
2. At one end of this space, a lens
3. Adjustment for focusing this lens
4. At the other end, a sensitive surface
5. A device for controlling the amount of light
6. A device for interrupting the light
From this list it is possible to reduce cameras to three fundamental components (in addition to the
assumed darkened space): (A) the optics, i.e. the lens (Nos. 2 and 3 in Mortensens's list); (8) the sensory
medium, i.e. the film (No.4); and (C) the exposure control, i.e. the shutter and a variable lens aperture
(Nos. 5 and 6). A fourth component might be a mechanism for aiming, framing, or previewing that includes
a focusing aid. It is primarily this fourth component that sets the RS apart from its Nikonos antecedents.
Following is a brief discussion of the components in the RS with respect to design, operation,
photographic results, problems encountered, and personal recommendations.
THE OPTICAL COMPONENT
The principal advantage of the Nikonos cameras has traditionally been' the uncompromised optical
quality provided by water contact lenses. These lenses increase the performance of the Nikonoses,
especially when compared to housed topside cameras, because the latter is an optical compromise.
Although semi-acceptable quality photographs can be obtained with correction ports, both curvature of
field and optical aberrations persist, especially in the corners of the image at angles of view greater than
90°. Dome ports also lose their effectiveness during focusing because of lens displacement from the
center of curvature. A great expense goes into the design and manufacture of topside lenses to minimize
the wide range of optical aberrations. An example is low dispersion glass used to reduce the tendency of
lenses to focus different colors (wavelengths) of light at different points. A similar level of optical correction
is possible only for lenses designed to focus in the water medium.
Scuba training includes lessons on the physics of light in relation to water. To the human eye,
objects under water appear to be magnified by the increased index of refraction of water compared to air
(the speed of light slows down by 33% in water). The optical effects are more complex than simply
magnification. The two most noticeable effects are: (1) the change in index of refraction which varies with
wavelength of light; and (2) the effect of the change in refraction increases with beam angle (increasing
from optical interface orthogonals). It is possible to see manifestations of these effects as color fringing
and distortion through a diving mask. The color fringing is easier to see at strong light contrasts such as at
the edge of a wall-mounted underwater light in a pool. The distortion is also easy to see through a diving
mask (Mertens 1970). However, optical effects other than the apparent magnification usually go
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Kline: Nikonos RS Evaluation
unnoticed by divers. Like the loss of color with depth, these changes appear exaggerated in photographs
compared to diver's perceptions because the camera does not employ the corrections of the mind1s eye.
Optical Adjustment
Although a few cameras have a preset focus (set such that infinity will be in focus), most have the
ability to adjust the focus setting. The adjustment can be based on a guess focus as the previous Nikonos
cameras. Some cameras employ a mechanical-optical device called a rangefinder (Ray 1979) used to
measure the distance to an object. The rangefinder can also be coupled to the lens (e.g. the Leica Mseries cameras). Other cameras require one to judge the sharpness of the lens-generated image on a
ground glass to set the focus. The lens used for the view finding can either be the same lens used to take
the picture {SLR cameras}, or a similar lens placed in parallel, such as in twin lens reflex cameras, e.g.,
Rolleiflex cameras for which the Rolleimarin underwater housing was made. The ground glass has evolved
into bright focusing screens through technological innovations (Ray 1979). Most recently, SLR cameras
have incorporated autofocus whereby the focus of the image is electronically analyzed and the lens
focus distance is adjusted via motors. The RS's appearance coincides with the timing of autofocus
technology development and is as much a victim as a benefactor of it.
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lI
Autofocus quickens focusing. For example, most housed manual focus cameras require several
turns of the focus knob to bring a lens from maximal to minimal focus distance. This makes it difficult to
switch from a distance setting to a close-up setting, as in photographing an approaching fish. In
comparison, the RS can shift the 50 mm macro lens from infinity to 1:1 (life-size, closest focus) in a couple
seconds. It is also difficult to discern the exact focus in housed SLR's reqUiring the use of small apertures
as compensation (increasing depth of field). The autofocus sensor in the RS can be considered an
electronic rangefinder. This provides superior evaluation of image focus, enabling one to use the entire
aperture range. However, the autofocus technology is evolving faster than the turnover time of Nikonos or
other pro-level cameras. The RS autofocus sensor is thus technologically behind more advanced, but less
specialist-targeted, cameras. The economics of designing and tooling for a specialist camera such as the
RS make it necessary to maintain a longer production period. Recommendation: Update the electronic
innards of the camera to fit on the current chassis. For example, the old Nikon F and F2 models were
equipped with a series of improved TTL meter finders while maintaining the same body design.
The RS autofocus has several operating modes that are discussed in detail in the operating
manual and elsewhere (Church 1994). The autofocus system is most useful in the S mode. The autofocus
system, however, had difficulty locking on to small « 10 cm) moving silvery fish (also problematical for
exposure) requiring the use of manual focusing. Manual focusing was also the only effective way to focus
on jellyfish and ctenophores and for magnification ratios approaching life-size (1:2 to 1:1). The superior
viewing and focusing (via the focus confirmation indicator) provided by the RS enabled accurate manual
focusing in these cases. Previously used cameras, including Nikonoses and housed Nikon and
Hasselblad SLR's focused much more slowly than the RS in P mode (manual).
I have not found a use for the freeze frame mode (F-mode) also known as trap focus.
Recommendation: I would like to see an "off" position to lock the focus at a given setting. This would
improve applications where one wanted to use a preset focus. For example, I was taking pictures of
spawning salmon in very shallow water (by squatting in the water while wearing waders and not using the
viewfinder) and unintentionally shifted the focus (in P mode, manual focus) while activating the shutter
with neoprene gloved hands.
Lens Mount
The RS incorporates a very secure double mounting system when compared to the old
Nikonoses. The inner mount, similar to the Nikon F mount, is used to align the optical, mechanical and
electronic components with the camera body. The outer mount provides the a-ringed pressure seal. This
extends the pressure hull of the body around the optical and mechanical components that are suspended
within the lens unit by springs. Additionally, there is a locking pin that prevents accidental twisting of the
lens under water. The absence of this feature occasionally resulted in pictures with two opposite corners
vignetted by built-in lens shade of the 15 mm UW lens.
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Optical Performance
Underwater photographs taken with the 50 mm macro and zoom lenses have all the attributes
expected of well-corrected lenses. The lenses are also quite usable at maximum aperture, f/2.8.
Autofocus enables accurate focusing under water; and in conjunction with large apertures, extends the
usable range of underwater strobes (e.g., 3 m with 100 speed film at f/2.8)
THE SENSORY COMPONENT
The sensory component consists of (1) the sensory medium, usually photographic film, (2) a
sensory (or recording medium) feeding and transport mechanism, and (3) devices for suspension of the
sensory medium in the focal plane (pressure plate and film guides). In the RS, the film advance and rewind
control is internalized which increases waterproof integrity compared to previous Nikonos cameras.
Otherwise, film transport and suspension in the RS are very similar if not identical to topside cameras.
Autoloading is found in most current cameras that use 35 mm film such as the RS.
Commentary
The RS has motorized winding and rewinding, which is expected to increase reliability because of
reduced number of lead-ins. Rewinding can be stopped by qUickly turning off the camera when the film
disengages the take-up spool (effected by rotating the shutter speed dial to L while raising it).
Disengagement is determined by a change in rewind motor pitch. This enables one to remove a partially
exposed roll. Thus a dive can be started with a full roll in the RS. Special attention needs to be given in
assuring that O-ring grease does not accumulate on the take-up spool. Recommendation: Handling film
(as in loading) after having just greased the O-rings will result in the transfer of grease to the portion of the
take-up spool that is under the pinch roller. A cotton swab will effectively remove O-ring grease
accumulation.
We are now seeing the incorporation of electronics into the sensory medium (CCO sensors) in the
new digital cameras. It is possible that a custom back will be developed for the RS for those interested in
underwater electronic still photography.
THE EXPOSURE CONTROL COMPONENT
The exposure control component has traditionally consisted of physical mechanisms which
control the quantity of light striking the sensory component. These are the shutter mechanism and lens
aperture (settings are known as f-stops). The purpose of the shutter is to control ambient light exposure
time. Innovations in recent decades have added measurement and integration of light measurement with
exposure control (first incorporated into the Nikonos line in the model IV-A). This initially consisted of
measurement and control of ambient light exposure often referred to as EE (electric eye) or TTL (through
the lens) light measurement. Artificial light output (strobe or electronic flash), commonly referred to as TTL
automatic flash (first incorporated in the Nikonos line in the model V) has also been added. More recent
advances include integration of exposure control of ambient light with strobe light using computer
technology and use of multisensor arrays. This is referred to as TTL automatic fill flash and matrix metering.
Implementation of this technology in the Nikonos RS is virtually a copy of topside camera systems.
To understand the exposure control functions, one must be careful to distinguish ambient light
and artificial (strobe) light measurement and exposure control. Ambient light is controlled by varying the
length of the exposure and the intensity of light entering the camera. Strobe light, however, is controlled
via duration of flash, f-stop, and strobe to subject and subject to lens distances. It is the measurement of
light by the sensors incorporated in the RS that can be confusing. In the RS, ambient light is measured in
two ways. First, by an array of five sensors (when the shutter speed dial is set to IIAIl); and second, by a
single center-weighted sensor (all other settings on shutter speed dial). The ambient light sensors
measure ambient light prior to the activation of the shutter release. The strobe light sensor measures light
during the actual exposure by sensing light reflected off the film. This sensor is located on the floor of the
camera chamber (between the lens and film) facing the film and is also center-weighted. Control of strobe
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light is effected when it is set to TTL and a predetermined quantity of light is received by the sensor. This
predetermined quantity of light is set by the camera1s on-board computer. When sufficient ambient light is
present and the shutter speed dial is set to IIA u , the computer will blend the ambient and strobe
exposures with what Nikon refers to as TTL matrix-balanced fill flash.
Recommendation: Be aware that it is only the ambient light that is being matrix metered! The
distinction between measuring ambient and strobe light should be more explicit in the RS instruction
manual. When the RS is set to a manual shutter speed, ambient light control becomes a manual operation
by varying the f-stop and shutter speed. When the strobe is set to TTL, strobe exposure will be automatic
via the strobe sensor. At the photographer's option, the strobe can be set to manual in which case the
strobe sensor in the RS is not used.
In my experience, the exposure control system largely resulted in properly exposed film. The
exceptional situation occurred when photographing silvery fish. The specular reflections of strobe light on
the highly reflective curved surface of the fish bodies tend to overexpose film. These reflections may also
be scattered by suspended particles further reducing image quality and are not a fault of the camera
system.
The RS automatically compensates for extension factors when focusing at close range.
Recommendation: This feature should be mentioned in the instruction manual or other literature currently
available on the R8. I determined that this feature exits during dry-firing of the camera during initial tests.
Nikon confirmed the existence of this feature (I. R. Perello, Technical Correspondent, Nikon Inc.,
T9rrance, CA, pers. comm.). The aperture settings are as for infinity. The infinity-setting light transmittance
is maintained as the lens is focused, the aperture numbers on the camera thus correspond to t-stops
rather than f-stops. Although this feature might simplify manual exposure settings, it reduces depth of
field in the macro range. For example, when the 50 mm lens is focused at 1:1 and aperture set at f/22, the
t-stop is 22 but actual f-stop is between 11 and 16. Therefore one should always set the aperture at f/22
when shooting in the macro range to maximize depth of field. Recommendation: It would be preferable to
be able to switch off the compensation so that a true f/22 would be available to those who desired it at
-1 :1.
RS Strobes
Discussion of the Nikonos 8B104 strobe is placed in this section because of the close relation of
strobe use to exposure control. Nikon introduced a greatly improved (over the 88102) wide angle
underwater strobe with the RS. The specifications are well publicized so are not delved into here. Nikon
has also recently introduced underwater disconnectable synchronization cords that alone may justify use
of Nikon brand strobes. Recommendation: This feature could be upgraded such that the fiber optic could
disconnect at both the camera and strobe. This would be a great idea for topside cameras as well. At
present, electronic signals must be converted from the camera and strobe requiring additional hardware
(part of these new connectors) causing a reduction in reliability. A future RS as well as strobes could have
optical ports into which the fiber optic would fit.
Recommendation: The SB104 would be improved with a built in modeling light like, e.g., Ikelite
strobes. Modeling lights are useful as a baCk-up dive light, as a focusing light (needed for SLR's), and as
an aiming light. A separate dive light used as a modeling light by being placed alongside the strobe is
unsatisfactory because of parallax (discordance in exactly where the strobe and dive light are aimed).
Mounting an adjustable dive light requires simultaneous adjustment of both strobe and dive light angles
which is cumbersome. Unfortunately, the recent upgrade of the popular 88103 to the 88105 also does
not include a modeling light. Thus one must seek out non-Nikon brand strobes. Non-Nikon strobes may
need electronic modification to prevent self-triggering of the camera. I have used suitably modified Ikelite
Ai/N and Ikelite dual head strobes (the latter is only available through AS Sea Photo in Los Angeles)
successfully with the RS. These strobes include modeling lights that work well as focusing light for low
light and night photography. Recommendation: Strobes equipped with a modeling light work especially
well for close-up photography of animals that are approachable only at night (e.g. pandalid shrimps).
The SB104 and both Ikelite strobes have had to have warranty work (in addition to RS adaptation
for the Ikelite models). In the case of the SB104, it failed on the second day at remote Soccoro Island. The
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electronic malfunction indication came on during a dive (no flooding indicated). It then functioned
intermittently during topside testing. Recommendation: Nikon must speed up repair time. For example,
Nikon took two months to make repairs while Ikelite performed their services inside three weeks.
RS VIEWFINDING
Underwater photographers have long regarded the 28 mm, 15 mm, and 20 mm UW Nikon lenses
as the finest mass-produced underwater lenses. Although the Nikonos cameras have excellent optics,
they are essentially box cameras. Here, I am referring to the fourth nonessential component of cameras.
Viewfinders do facilitate better pictures. The viewfinders used in underwater photography in the old
Nikonos models consisted of separate units mounted on the top of the camera. These viewfinders give a
very poor preview of what the final picture will look like. Underwater photographers have accepted the
compromised optical quality concomitant with housing their topside SLR cameras to gain the SLR
advantage - the ground glass image projected by the taking lens showing virtually the same image that will
be exposed on the film. Not enough superlatives can be used to describe the underwater photographic
preview enabled by the RS. Recommendation: The electronic display (which is very easy to see) should
have the following added to it:
1. Lens to subject distance. More specifically, lens front element to subject distance, instead of focal
plane to object distance or make the choice user selectable.
2. Frame number. The frame number in its present location is very difficult to see; while numbers in
the viewfinder are very clear. Furthermore, constantly observing the frame number would be more
effective in budgeting a roll of film.
3. An indicator showing activation of the focus lock.
ADDITIONAL PROBLEMS
In addition to problems already discussed, I have had a few others:
Separated Prism. The prism separated shortly after I received the camera. This appeared to be a
manufacturing defect. Nikon returned it in less than a month (the Norcross, GA repair facility was still open).
Shutter Release. During one dive the shutter release locked-up, probably due to sand in the
external mechanism located under the cowling that forms part of the hand grip. This problem was selfcured during the return to the surface and has not recurred.
Electrical Contact. During a recent dive I found the aperture read-out in viewfinder to be replaced
by dashes (F--, as when no lens is on camera) and so was not able to know if the correct aperture was set.
The effect on flash was consistent with the smallest aperture that the RS was set to. Additionally, the focus
was also locked at one distance (which happened to be 1:1 because I was using the 50 mrn lens). The
problem was corrected when the lens was removed and remounted. The probable cause was poor or
incomplete electrical contact. Electronic contact is a weakness in a camera designed for use in humid
environments. Recommendation: Like the flash connection, the lens - body communication could benefit
from fiber optics. However, electrical power might continue to be required for electronic functions in the
lens.
MAINTENANCE
The RS, like all equipment used in the underwater environment, is maintenance intensive.
Although the RS does not require the careful alignment of external controls as with housed cameras, one
must be very careful in maintaining the O-ring seals. Warkentin indicated that a flooded RS body or R-UW
lens is probably not worth repairing (B. Warkentin, Southern Nikonos Service Center Inc., Houston, TX,
pers. cornm.). Recommendation: Users should be informed that because the RS O-rings are made of
silicone rubber, they should not be used with silicone O-ring grease. Additionally, the amount of O-ring
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grease used on the orange RS O-rings should be more than used with previous Nikonos cameras (A.
Broder, AS Sea Photo, Los Angeles, CA, pers. comm.). Frink (1994) recommended that one operate all
the controls while the camera is submerged in the freshwater rinse. Early in the use of the RS I did not
check the compensation dial to make sure it was set to zero after doing the rinse and was not cognizant of
the indicator in the finder (which could be improved) during shooting the sUbsequent roll of film and so
overexposed it. I learned from Bob Warkentin when he did the annual overhaul of the body that the rubber
boot around the eyepiece is removable and should be removed for rinsing after use. The consequence of
not having done so was that corrosion had locked two of the stainless steel screws into place.
Recommendation: Instructions for this aspect of maintenance should be added to the instruction manual.
Recommendation: The instruction manual could use a complete overhaul. It attempts to provide a
mini-course in photography (e.g. explaining depth of field rudiments on p. 69) instead of providing
complete technical data on the operation, specifications and maintenance (e.g. depth of field tables
instead, particularly important as depth of field is not marked on the lens barrels).
SUMMARY
Given three years of experience using the RS and comparing the results obtained with other
underwater still cameras including all the previous Nikonos models (except for the IV-A), and housed
Nikon, Hasselblad and Rolleiflex cameras I can give the RS my endorsement as a tool for scientific
underwater photography. The most outstanding criterion is the high percentage of "keepers," a virtual
mirror image (i.e. reversal) compared to results obtained with other cameras. That is previously, most
underwater shots were "discards" instead of "keepers" as with the RS. The bottom line in evaluating the
RS is based on the results it delivers, which it does.
ACKNOWLEDGMENTS
Kim Antonucci provided editorial assistance during the preparation and revision of this
manuscript.
LITERATURE CITED
Church, Jim. 1994. Jim Church's Essential Guide to Nikonos Systems. Aqua Quest Publications, Inc. New
York.
Couet, Heinz-Gert de and Green, Andrew. 1989. The Manual of Underwater Photography. Verlag Christa
Hemmen. Wiesbaden, Germany.
Frink, Stephen. 1994. The Nikonos RS in the Red Sea. Ocean Realm April 1994:87-95.
Hillebrand, Rudolf and Hauschild, Hans-Joachim. 1993. Nikon Compendium. Have Books, East Sussex.
McNeil, Gomer T. 1972. Optical Fundamentals of Underwater Photography. Second Edition. Mitchell
Camera Corp., Rockville, MD.
Mertens, Lawrence E. 1970. In-Water Photography. John Wiley & Sons, Inc. New York.
Mortensen, William. 1940. Mortensen on the Negative. Simon and Shuster, New York.
Ray, Sidney 1979. The Photographic Lens. Focal Press, London.
Wakimoto, Zenji. 1967. On designing underwater camera lenses. Photogram. Eng. 33:925-936.
Wu, Norbert. 1994. How to Photograph Underwater. Stackpole Books, Mechanicsburg, PA.
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