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Nikonos A short history and description of the Nikonos camera system

The Nikonos Camera started life as the Calypsophot, designed for Jacques Cousteau, in 1956, by the Belgian engineer Jean De Wouters. The original lens was a Som Berthiot 35mm f/3.5, with a flat glass front port, mounted on a special waterproof bayonet.

calypso_b calypso_c

The design was subsequently offered to Nikon, who had the technical and marketing infrastructure to make it into a commercial product, and the first 'Calypso-Nikkor' camera became available in 1963 (a prototype of this original Nikon version appeared as a gadget in the 1965 James Bond film 'Thunderball').  The design evolved from 1963 to 1979, with the major revisions being known as the Nikonos, the Nikonos II (1968), and the Nikonos III (1975). The important change, from a compatibility point of view, was that the III came with a new type of flash connector. This change was necessary because the original connector was unreliable. The Nikonos connectors which came later are compatible with the Nik III, but not with the earlier cameras.

Nikonos III
Nikonos III

Nikonos III exploded view
Photomontage: D. W. Knight © Cameras Underwater Ltd. 2006

Nikonos IVa
In 1979, Nikon decided that it was time for a radical redesign; to simplify production by having more parts in common with other Nikon cameras, and to improve exposure accuracy by using a Seiko electro-mechanical shutter. Thus was born the Nikonos IVa (the 'a' stands for 'automatic exposure', there was no IV on its own); which was unpopular because of its lack of manually controllable shutter speeds, and the fact that any leak could stop it from working (the original cameras would often work again after being rinsed out and dried). The Nik IVa system also included an automatic Speedlight, the SB101, and a feature whereby the camera would be automatically switched to the 1/90 s flash sync speed whenever the flash was ready to fire. The IVa used the same 3-pin sync connector as the III, but with the old 'bulb' flash contact now used for the 'flash ready' signal.

Nikonos V
Nikonos V front
The Nikonos V ("Nik five") appeared in 1984. This gave the user the option of manual shutter speeds, a half-decent built-in lightmeter, and introduced TTL automatic flash. The TTL feature required a new 5-pin flash connector, and compatibility was maintained by the clever wheeze of making the the two extra pins in the camera socket spring-loaded, so that they would be pushed back out of the way when a Nikonos III plug was inserted. The companion plug has two flat contacts, which mate with the sprung pins of the V, but are simply ignored by the III and IVa. This feature gives at least manual flash compatibility across the whole Nikonos range from III onwards, but it meant that you had to make sure that the flat contacts were clean before inserting the plug. The Nikonos V connector is still used on modern underwater housings. nik5_xsect

nikv_pl The Nikonos V
flash connector

Some facts about the Nikonos V
dot_rd The Nikonos V is not an SLR camera.
dot_rd The Nikonos V does not have a rangefinder.
All Nikonos (pre RS-AF) lenses were designed for focusing by estimation. This would appear to require either skill or measurement on the part of the user, except that the camera was not normally used in that way. For underwater use, the camera was normally fitted either with a wide-angle lens, or with a macro attachment. Wide-angle lenses do not require focusing in the normal sense - for most purposes they are best set to the hyperfocal distance, i.e., the upper depth of field mark is placed at ? . Macro attachments are provided with distance prongs and framers, and so do not require focusing except for adjustment to the recommended setting.
wa The principal advantage of the Nikonos was the ability to use fully water-corrected lenses in wide-angle photography.
dot_or The Nikonos V was for many years the industry standard professional underwater camera, but became obsolete with the advent of high-resolution digital photography (>4Mp). Nikon attempted to replace it in the early 1990s with the Nikonos RS-AF (Reflex System - Auto Focus), essentially an underwater F4, but the new camera was fabulously expensive and few could justify the cost. The RS-AF was soon discontinued except for fulfilment of existing government contracts, and Nikon instead continued to market the Nikonos V until 2001.
dot_rd For slightly more than the cost of servicing a Nikonos V, it is nowadays posible to buy an underwater digital camera and housing which will exceed the performance a Nikonos with its standard 35mm lens (photography has moved on).

Nikonos V Camera Features
n_n5o n_n5g

dot_or dot_gn Made in two colours; orange and camouflage green (intended for press photographers operating in jungle war zones, the Nikonos II and III models having been used extensively during the Vietnam War).
dot_bu Nikonos cameras and system components designed for use underwater are conservatively rated to a depth of 50m.
film 35mm film, 36 x 24mm format.
Modes: Manual, Aperture Priority Auto, TTL Flash, & B.
Shutter speeds: Man 1/30 to 1/1000s, Auto 30s to 1/1000s, special M 1/90s mode works without battery.
dot_zap X-sync @ 1/90, 1/60, & 1/30s.
Film speeds: ISO 25-1600 (25-400 for TTL flash). External ISO selector allows exposure bracketing.
Viewfinder built in for 35mm lens (full field corresponds to 28mm view). Viewfinder LED display gives metered speed and flash status. A standard accessory shoe on the top of the camera allows viewfinders for other lenses to be mounted.

Speed Control
The speed control gives manual (electronic) shutter speeds from 1/30 to 1/1000s. The A (auto) position gives aperture-priority auto-exposure with speeds from 30s to 1/1000s. In A mode, the camera is set to the X-sync speed of 1/90s when a Nikonos V (TTL) compatible flash unit is connected and ready to fire. In manual-electronic modes (1/30 - 1/1000s) the flash ready signal sets the camera to 1/90s only if a higher speed is selected, ie., flash sync is possible at 1/30, 1/60, and 1/90s.

 The battery is disconnected in M90, B and R modes, and battery drain is minimised if the camera is left in one of these modes when not in use. M90 (mechanical 1/90s) is a special mode which allows the camera to be used when the battery is dead. B mode is used for time exposures - the shutter remains open for as long as the shutter button is pressed. Since the camera is not powered in M90 and B modes, there is no TTL flash control when using these settings, but manual flash working is possible. R (rewind) position disengages the film-advance mechanism to allow the film to be rewound into its cassette.

Frame Counter
The frame counter (next to the speed control) is reset to 'S' (start) when the camera back is opened. A switch in the frame-counter mechanism disconnects the battery until frame '1' is reached. If an electronic mode is selected, the shutter will fire at approx. 1/1500s until the counter indicates '1'.

iso_ctrl Film Speed (ISO / ASA) Control.
The external ISO control, normally set to the film-manufacturer's recommendation, can be used for exposure bracketing when using electronic modes. The available ISO range is 25 to 1600 when using ambient light, and 25 to 400 when using TTL flash. True Nikonos-V compatible strobes (Nikon and Ikelite) give an error signal if an ISO value of greater than 400 is selected.

Shutter release and Lock.
Protruding shutter button allows the camera to be used while wearing gloves. The Lock-lever (L) prevents accidental firing. Lightly pressing the shutter button activates the viewfinder display. The display remains on for 16sec if the battery is in good condition, but goes out immediately on releasing the shutter button if the battery is low.

The frame markings within the viewfinder area are for the 35mm lens, and correspond to 85% coverage at ?. Parallax compensation mark indicates the shift required when working at 0.8m
The LED display at the bottom of the viewfinder indicates selected shutter speed, over exposure warning, under exposure or camera shake warning, and flash ready. In manual-electronic modes, the camera-metered speed flashes if different from the selected speed.

Nikonos Maintenance
If you are thinking of taking a Nikonos camera underwater, you should probably think again. Photography has moved on, and a cheap digital camera and underwater housing can (with the aid of image processing sortware) be made to produce results as good as or better than those which could be obtained with the venerable Nikonos.  Rather than simply deleting the advice we gave years ago however, we will assume that you want to dive with a Nikonos camera for some special reason, such as that of making a historical movie.

Power source is a DL1/3n 3V Lithium Cell.
2x S76 silver cells can also be used, but the lithium cell lasts longer.
Replace battery when the terminal voltage falls below 3.00V

Nikonos IVa and V use the same battery holder.
syncplug Sync blanking plug (inc O-ring)
Waterproof blanking cover, for Nikonos 1-5 & RS (M14 x 1.0).
ork_n5 User O-ring set.
Back door, Lens, Battery holder, and sync socket.
Standard Nikonos O-rings are made from Nitrile-Butadiene rubber (NBR) with a Shore hardness of about 60 (softer than standard O-rings which are usually Sh~70).
The Nikonos grease supplied in the O-ring kit is petroleum gel (Vaseline). Silicone grease (e.g., Dow Corning Molykote 111) is far superior (less soluble in water and highly water repellent).

If you obtain a secondhand Nikonos camera from a private seller, or have a Nikonos camera which has not been submerged for some time, taking it underwater without getting it serviced is asking for trouble. The most heavily stressed O-ring seal in the Nikonos V camera (and in the IVa) is that around the film advance lever shaft. It tends to dry out and become abraded, giving rise to a slow but insidious leak into a delicate part of the camera mechanism known as the 'winding stack'.

A full service for a Nikonos V involves complete replacement of non-static O-rings, housing only pressure test, full function test, recalibration of the light metering system, and final pressure test, with fixing of trivial faults and adjustments along the way. The procedure requires camera calibration equipment, a pressure tank, special tools, hole plugs and electrical adapters, and access to the service manual. Individuals who do not possess advanced technical skills and a well-equipped workshop are advised not to attempt it.

What should I do if I flood a Nikonos V?
Do the following within the hour:
dot_k Switch off (set to M90).
dot_k Remove the lens, the film, and the battery.
dot_k Remove the plate covering the electronics section (4 small screws).
dot_k Set the ISO/ASA knob to 100. Use a fingernail to pull out the clip which holds the ISO knob (use of pliers carries the risk that you will scratch the back-door O-ring seat). Pull out the control assembly by the outer knob.
dot_k Prize off the plastic cap which covers the film advance lever (if fitted) and throw it away (it serves no useful purpose). Unscrew the film advance / speed shaft from the top. Pull out the control assembly by the speed knob.
dot_k Remove the 3 Philips screws which retain the inner body (1 in the film-cassette well, 2 in the take-up spool well).
dot_k If you have a soldering iron, unsolder the 5 flash connector wires (blue, yellow, violet, green, black) next to the ISO control.
dot_k Pull out the inner body (thumb in the film-cassette well, forefinger between the film-advance sprocket and the take-up spool). verboten Don't put your fingers anywhere near the shutter.
dot_k Flip the inner body over. verboten DO NOT tug on the flexible printed circuit which connects to the viewfinder LED assembly.
dot_k Release the LED display from the viewfinder by undoing 2 screws which secure the LED mounting plate to the housing. warn Use the correct size of watchmaker's screwdriver and take care not to shear the screws or damage the screw-heads. If you cannot remove these screws without causing damage, you can undo the clamp which joins the two flexible printed circuits; but re-connection is a tricky operation.
dot_k If you were able to unsolder the wires leading to the flash connector, the camera mechanism is now free in your hand. Repeatedly wash the affected parts with distilled water. Washing works by serial dilution, ie., the 1st rinse removes about 95% of the salt, the next rinse removes 95% of the remaining 5%, and so on. Try not to get unaffected parts wet, but for a serious flood, was everything over and over again with fresh distilled water.
verboten DO NOT wash the mechanism with industrial alcohol. Alcohol will dissolve all of the lubricants and adhesives used in production, and will cause the mechanism to become an economic write-off.
dot_k Allow the camera to dry naturally in a warm place, or warm it gently with a hair-drier to speed things up.
dot_k If you have identified and corrected the cause of the flood, fit the speed control and film advance lever to the camera mechanism and check that it functions mechanically. If there is any water in the shutter assembly, the shutter will stick and further drying time is needed. When mechanical functionality is restored, install the battery and check electronic functionality. If all is well, the camera mechanism can be re-installed into the body. Clean out all of the O-ring grooves with paper towels, re-grease the O-rings, re-assemble the camera, and check all functions. Don't forget to clean and re-grease the O-rings of the controls which have been disturbed (ie., ISO Knob, and 3 rings on the speed/advance control shaft).
verboten Do not remove O-rings from their grooves using screwdrivers or other sharp tools. Handle O-rings only with the soft parts of your fingers. O-rings which cannot be removed by hand can be removed by carving a tool out of soft plastic.
dot_k Get the camera serviced and professionally reassembled as soon as you get back to civilisation.

Nikonos Lenses
The Nikonos camera system has a very large range of lenses associated with it; primary optics having been manufactured by Nikon and Sea&Sea, and other lens accessories having been made by various manufacturers. All can be used with any manual focus Nikonos (or Calypsofot) model (not the RS-AF), with the exception that early versions of the Nikonos 15mm f/2.8 are incompatible with the TTL metering system of the Nikonos IVa and V. Nikon used the terminology 'W-Nikkor' for a waterproof lens corrected for use in air (recognisable by the flat front glass), and 'UW-Nikkor' for a lens corrected for use underwater (and having a convex or concave front glass). Nikon also made an LW-Nikkor 28mm f/2.8 lens, for use in tropical conditions (air corrected, not submersible). All of the W-Nikkor lenses focus in water, but of the UW-Nikkor lenses, only the 28mm f/3.5 will focus in air. One of the principal advantages of the Nikonos system was the availability of water-corrected lenses, which (before the advent of software radial correction) always gave a higher resolution than an equivalent air-corrected lens mounted behind a port.

Nikonos Lens Syschart.

Underwater resolving power of Nikonos lenses
UW Nikkor 15mm f/2.8: 73 lines/mm centre @ f/8.
UW-Nikkor 28mm f/3.5: 72 lines/mm centre @ f/8
W-Nikkor 35mm f/2.5: 62 lines/mm centre @ f/8
Source: 'Diver-operated cameras and their marine biological uses', A. Svoboda, in 'Underwater Photography and Television for Scientists', J.D.George, G.I. Lythgoe, and J.N. Lythgoe, 1985, ISBN 0-19-854141-4 (OUP).

An air-corrected wide-angle lens behind a dome port, no matter how expensive, will always give lower edge resolution than a properly water-corrected lens. This is due to the introduction of chromatic aberration at the air-water boundary. If the camera is a digital camera however, or if the film is to be scanned, it is possible to correct for chromatic aberration using software. If software correction is applied, a good air-corrected lens can be turned into a good water-corrected lens, and results similar to or better than those obtained with UW-Nikkor lenses can easily be achieved.

Nikonos Air / Water Lenses and Viewfinders
W-Nikkor 35mm f/2.5
Standard lens, works in air and underwater.
Coverage: 62° in air, 46°30’ in water.
Resolution: 62 lines/mm, centre, at f/8.
Min focus: 0.8m. Min aperture f/22. Filter thread 58mm.
Normally used with extension tube or supplementary lens.
W-Nikkor 80mm f/4
Normally used underwater with the Nikonos close-up outfit (for 1:2.2 macro) - gives better resolution than the 35mm lens with extension tube.
Coverage: 30°20’ in air, 22°45’ underwater.
Min focus distance 1m. Min aperture f/22.
Filter thread 58mm.
Bare lens is difficult to focus underwater due to very small depth of field.
UW-Nikkor 28mm f/3.5
Moderate wide-angle rectilinear lens, offering easier focusing and greater resolution compared to the 35mm lens. Designed for underwater use, but gives acceptable results in air.
Resolution: 72 lines/mm, centre, at f/8.
Coverage: UW 59°. Min focus 0.6m. Min aperture f/22.
Filter thread 58mm.

ff3580_r Action finder 35/80mm
Rapid underwater framing for the 35/2.5 and 80/4 lenses.
ff28_r Action finder 28mm
Rapid underwater framing for the UW-Nikkor 28mm lens.
df10_ DF10 80mm Optical Viewfinder
Optical finder for the W-Nikkor 80mm f/4, with parallax adjustment.
verboten Not Submersible!

Lens Accessories
hood_35 Rubber Lens Hood
Rubber lens hood for the 35mm/2.5. Provides complete knock protection in rough working conditions.
lensprot58 Lens Protector Ring
Lens protector ring 58mm. Fits 80, 35, & 28mm lenses. Prevents damage to filter thread in rough conditions. Can be removed in water to allow fitting of optical accessories.
lenscap58 Spare Front Lens Cap
Spare 60mm slip-on lens cap, for 80, 35 & 28mm lenses.
lenscap_r Spare Rear Lens Cap
for all manual focus Nikonos Lenses (not RS).
lenscases Lens Case CL50A (35&28mm)
Lens Case CL51 (80mm)
Hard lens carrying case, black leatherette.

Nikonos Wide-angle Lenses & Accessories
dot_or The focal length of a lens in water is not directly comparable to the focal length of a lens working in air. The parameter of interest is the Angle of Coverage. E.g., the 15mm UW Nikkor has the same coverage (94°) as the 20mm Nikkor f/2.8 lens used on Nikon F series SLRs.
dot_gn The Sea&Sea 15 and 20mm Nikonos mount lenses were a low cost alternative to the UW-Nikkor counterpart. They gave good results, but used a simplified version of the Nikonos bayonet, which did not preserve the back-focal distance exactly, taking its reference from the front of the camera housing rather than from the inner body. Hence image sharpness could vary slightly depending on the camera tolerances and whether or not the lens was pushed firmly into the camera.
warn Nikonos underwater wide-angle lenses do not focus in air!
ss_swl16 Sea&Sea SWL16 wide adapter
Sea&Sea 16mm Super Wide conversion lens for the W-Nikkor 35mm f/2.5. Screws into the 58mm filter thread.
Can be attached & removed in water.
Depth of field: 0.6m-infinity @ f/8.
Max aperture f/5.6. Coverage 91° (Not designed to focus in air).
vf17mh80 Sea&Sea VF-17 #0140
Optical viewfinder with parallax adjustment knob.
Optical elements are acrylic.
90° coverage, suitable for 15-16mm lenses. Was also Supplied with masks to modify coverage for use with 35 & 20-24mm lenses.

nwl20a Sea&Sea NWL20 20mm f/3.5
Low cost alternative to the Nikon 20mm lens.
Angle of coverage 79.31°.
Min focus distance 0.4m.
Smallest aperture f/22.
Filter thread 58mm.
Suitable viewfinders: VF15, VF17, DF12.
vf15 Sea&SeaVF15 Optical Viewfinder
All glass optics.
High eyepoint finder, 96° coverage, with internal markings for 35, 20 and 15-16mm lenses.
warn For underwater use. View will appear out of focus in air.
nwl15a Sea&Sea NWL15 15mm f/3.5
Low cost alternative to the Nikon 15mm lens.
Angle of coverage 96°.
Min focus distance 0.3m.
Smallest aperture f/22.

Sea&Sea SWL-Fisheye 12mm f/3.5
pic_wl12 nwl12_1
nwl12_2 Angle of Coverage: 167°.
Full frame fisheye.
Min focus distance: 0.3m.
Minimum aperture: f/22.
Depth of field at f/22 is 0.13m - ? (the near subject just touching the front lens element).
Supplied with Neoprene dome protector and bag.

Fisheye lenses impart outward curvature (pincushion distortion) to any straight lines which do not pass through the centre of the field, but eliminate much of the perspective distortion associated with rectilinear wide-angle lenses. Fisheye distortion may be used as a creative effect, or may be minimised in pictures without dominant geometric elements by making any horizon line pass through the centre of the field.
Sea&Sea Fisheye Viewfinder VF12
Coverage: 150.3°
(90% of the 12mm fisheye frame).
Oversize eyepiece allows full frame viewing with diving mask.

uwn20_1 UW-Nikkor 20mm f/2.8
Water corrected, rectilinear high-resolution lens.
Angle of coverage 78°.
Min focus distance 0.4m.
Smallest aperture f/22.
Filter thread 67mm.

df12_ DF12 20/28mm Optical Viewfinder
Nikon optical viewfinder for the UW-Nikkor 20mm lens. Magnification 0.35x. Coverage 85%.
Supplied with detachable mask to modify coverage for use with the 28mm lens. With internal parallax markings.

Nikon UW-Nikkor 15mm f/2.8
uwn15 dot_gy Water-corrected rectilinear wide-angle lens.
dot_gy Retro-focus optic compatible with TTL light-metering systems of Nikonos IVa and V.
test Resolution: 73 lines/mm, centre, at f/8.
cov Angle of coverage 94°.
dot_gy Min focus distance 0.3m.
dot_gy Smallest aperture f/22.

Depth of field scale, in side window, mechanically linked to the focus and aperture controls, makes this lens extremely easy to use. Normal practice is to choose the working aperture and set the focus so that the upper depth of field marker is on infinity (hyperfocal mode). The lower depth of field marker then gives the minimum working distance, as follows:
Aperture Depth of field
(relative to film plane)
To get the minimum distance relative to the lens front element, subtract 11cm; eg., at f/22, everything more than 10cm from the front element will be sharp.
A typical flash / ISO 100 film combination gives a working aperture of f5.6 - f/8. With more attention to focusing, the lens can easily be used with ISO 25 film.
f/2.8 1m - ?
f/4 0.7m - ?
f/5.6 0.5m - ?
f/8 0.4m - ?
f/11 0.31m - ?
f/16 0.26m - ?
f/22 0.21m - ?

df11_ DF11 15mm Optical Viewfinder
Nikon companion optical finder for the UW-Nikkor 15mm. Magnification 0.24x. Coverage 90%. Built-in parallax compensation marks for 0.6m and 0.3m

Nikonos Close-up and Macro accessories
The most popular macro accessory for the Nikonos was a set of extension tubes for the 35mm f/2.5 W-Nikkor. Nikon however, did not make extension tubes (although it allowed some to be badged as Nikon products), because the extension tube forces the 35mm lens to work well outside of its design focusing range and results in rather poor resolution. The table below gives the maximum achievable centre resolution (in lines/mm) for various common macro lens configurations; from which it can be seen that an SLR macro lens with a flat port, in addition to its freedom from prongs and framers, gives considerably better results than the Nikonos 35mm f/2.5 (other SLR macro lenses are likely to give similar results to those in the table, because the port is the major resolution limiting factor). The 28mm f/3.5, on the other hand, gave better performance than an SLR either with the Nikonos close-up outfit, or with an extension tube. Note that the Nikonos Close-up lens is an achromatic doublet, and cheaper single-element close-up lenses give inferior results.

Resolution in lines/mm of some camera systems*
Lens Configuration 1:6 1:4 1:3 1:2 1:1
55mm Micro-Nikkor + flat port. 65 53 52 47
UW-Nikkor 28mm + Nikonos Close-up lens 82
UW-Nikkor 28mm + Extension tube 60 55 40
W-Nikkor 35mm + Nikonos Close-up lens 48
W-Nikkor 35mm + Extension tube 50 37 36 36
* Source: 'Diver-operated cameras and their marine biological uses', A. Svoboda, in 'Underwater Photography and Television for Scientists', J.D.George, G.I. Lythgoe, and J.N. Lythgoe, 1985, ISBN 0-19-854141-4 (OUP).

Nikoncuk_1 Nikonos Close-Up Outfit
2 element Achromatic Close-up lens, for use with Nik3/4/5 & 28, 35, or 80mm main lens; with distance piece, subject frames, and stabilising bar which attaches to the accessory shoe.
Reproduction ratio depends on main lens as follows:
80mm Lens: 1:2.2 (UW), 1:3 (air).
35mm Lens: 1:4.5 (UW), 1:6.5 (air).
28mm Lens: 1:6 (UW).
Nikonos CU outfit

ikxtube Ikelite Extension tubes and framers for 35mm lens.
Lightweight corrosion proof moulded extension tube, with removable black stainless steel framer, for the W-Nikkor 35mm f/2.5. Tube fits between the main lens and the Nikonos camera body, and cannot be changed underwater. 1:1 tube gives life-size image on the film. 1:2 gives 1/2 life-size. 1:3 gives 1/3 life size.
#4090.11, 1:1 extension tube and framer.
#4090.12, 1:2 extension tube and framer.
#4090.13, 1:3 extension tube and framer.

ssxtube Sea&Sea Extension Tubes for 35mm lens.
Extension tubes with distance piece and removable framer prongs. Framer prongs can be unscrewed and clipped underneath to avoid shadow when using side-lighting. Tube fits between the main lens and the Nikonos camera body, and cannot be changed underwater.1:1 tube gives life-size image on the film. 1:2 tube gives 1/2 life-size. 1:3 tube gives 1/3 life size.
SS35m3, 1:3 tube for 35mm lens.
SS35m2, 1:2 tube for 35mm lens.
SS35m1, 1:1 tube for 35mm lens.

ssxtb28 Sea&Sea SS28m2 1:2 tube for 28mm lens
Sea&Sea 1:2 extension tube for the UW-Nikkor 28mm f/3.5 lens. Gives half life-size image on the film. The 28mm lens with an extension tube achieves considerably greater resolution than can be obtained with the equivalent 35mm lens setup.

Nikonos Flash Systems
Flash systems for the Nikonos were made by numerous manufacturers; and many modern underwater strobes still support the Nikonos TTL flash protocol. Note that the Nikonos TTL flash interface is electrically compatible with pre-digital Nikon TTL cameras (except the F3); which meant that photographers could use a Nikonos for some shots (ie., wide-angle) and a housed Nikon 35mm SLR for others (eg., macro), and share the same flash unit between the two systems.

The Nikon electronic flash systems for the Nikonos were, in historical order, the SB-101, SB-102, SB-103, SB-104, and SB-105. The SB-101 (pre-dating the Nikonos V) was a manual flash unit with an optional SU-101 auto-sensor. The battery compartment for the SB-101 was separate from the flash head, inside the handle, and the use of anodised aluminium with brass screws (a strong corrosion cell) made the battery compartment impossible to dismantle after a year or so of underwater use. Hence, flooding the SB-101 battery compartment tended to make it a write-off. The SB-102 was the first TTL flash unit for the Nik V, but could also use the SU-101 auto sensor for compatibility with the Nik IVa. The SB-103 was a smaller flash unit, physically similar to the later SB-105, which replaced it. Neither the SB-102 or the SB-103 had sealed battery compartments, and the SB-103 was subsequently recalled because it represented an explosion hazard in the event of a battery compartment leak. The SB-103 had the interesting feature that the high-voltage circuit-board tracks ran perilously close to the connections of the integrated circuit which managed the TTL flash signals - hence one drop of water through the battery cover seal and the whole thing could die. This unfortunate heritage led Nikon to go for a completely over-the-top solution with the SB-104, the electronics compartment being completely sealed, fitted with oxygen absorbers, and filled with dry nitrogen. Servicing the SB-104 was thus a highly specialised job, but the strobe was reliable. The last in the line was the SB-105, which had a sealed battery compartment and was well designed and straightforward to repair. The SB-104 and SB-105 can still be used with some non-preflash digital cameras (the flash control circuitry is too sluggish to handle pre-flashes).

Notice that Nikon never got away from the lamentable 'standard lighting' configuration, with the strobe on the left side of the camera. The best place to put a single strobe is directly above the camera in normal circumstances, and having to detach the strobe from the tray so that it can be hand-held in the correct position is somewhat unergonomic. Hence, many users preferred to replace the Nikon bracket with a fully articulated lighting arm (Ikelite, TLC, Ultralight, etc.).

Nikon TTL flash for Nikonos SB-104 SB-105
Operating modes: TTL auto, Manual full, 1/4. 1/16, Slave. 
Guide No (Full, ISO 100, UW): 16 10
Angle of coverage: 100° 100° w diffuser SW-103
Colour temp: 4700K
Power source: Ni-CD pack SN-104 4 x AA, NiCd or Alkaline
Flashes per charge (approx): 120 45 (Ni-Cd), 120 (Alkaline)
Recycle time (approx): 3 sec. 4s (Ni-Cd), 6s (Alkaline)
Dimensions (head only)/mm: 124 dia, 222 L. 99W,, 130H, 181D
Weight (w/o battery) 1.99 Kg 0.78 Kg
Depth rating: 100m 100m

Non-underwater Flash accessories
Nikonos to PC sync adapter
verboten Not submersible! Adapts Nikonos III / IVa / V to work with conventional manual land flash via PC lead.
Nikonos TTL hot shoe adapter
verboten Not submersible! Adapts Nikonos V to work with Nikon hot-shoe compatible TTL flash units. Operation with Nik III and IVa is manual only.

Secondhand Nikonos Equipment.
The Nikonos camera system is obsolete.  A digital underwater camera and housing can be obtained for little more than the typical cost of servicing a Nikonos V. Hence the only reason for taking Nikonos equipment underwater is so that people can be filmed or photographed with it.  If not dissuaded, the following advice might be helpful:

If buying secondhand Nikonos equipment with the intention of using it underwater, you need some kind of guarantee from the seller. A considerable proportion of the equipment offered for sale by private individuals turns out to be faulty, often in some subtle but insidious way, and spare parts can be hard to obtain. The classic problem of the Nikonos III was that of a cracked top-plate, which was caused by lending the camera to someone who didn't know that you have to remove the lens before you can get the camera open. You'd think that this problem would have been rare, but it was our most common reason for declaring a Nikonos III to be a write-off. The Nikonos II had a cast aluminium top plate, but the author has even seen one of those broken in two by someone who tried to remove it with a hammer and chisel (which goes to prove that there really are people from other planets walking amongst us). Nikonos IVa and V cameras tend to leak into the winding stack, so take off the electronics cover plate and have a good look for corrosion. The TTL flash system of the Nikonos V will cease to work if the sync socket has been flooded (the springs in the TTL contact pins corrode and cease to conduct electricity). It follows that signs of tender loving care are good, but signs of abuse are very bad. The important issue to understand however, is that Nikonos camera systems are like cars; in that they consume parts as a proportion of the operating cost, and occasionally need expensive repairs. Before committing money to a system which is no longer in production, address the problem of how it will be maintained.

Here is the maintenance status of some common and less common items of Nikonos equipment as of 2006 (there really is no point in updating the following information):

Calypsophot (1958-1963):- Collectable.
Calypso-Nikkor / Nikonos (1963 - 1968):- arguably collectable.
Nikonos II (1968-1975):- No spares (o-rings available).
Nikonos III (1975-1979):- No spares (o-rings available). Worth maintaining with reclaimed and substitute parts. Write-off if camera top is cracked.
Nikonos IVa (1979-1984):- No spares except o-rings and parts common to Nik V. Write-off if film-advance return spring is corroded.
Nikonos V (1984 - 2001):- Spares still available in 2006, but at 5 years since discontinuation, this situation may not last much longer.
W-Nikkor 35mm f/2.5 & UW-Nikkor 28mm f/3.5 - last production versions are black anodised. Old versions are plain aluminium and are less valuable. Look out for dented filter rings, scratched optics, stiff controls, and internal flood residues - all of which are very bad news.
UW Nikkor 15mm f/2.8 - there are two versions of this lens. The old version with the back element projecting into the camera throat has no spares, and does not work with the Nikonos IV and V auto exposure systems. The focus scale window is acrylic, and will crack if the lens is cleaned with alcohol.
LW-Nikkor 28mm f/2.8 - This is a 'land waterproof' lens for use in rainforest environments (Vietnam war press photography). It cannot be used underwater, but few were produced and the item is collectable.
SB101:- No spares. Unrepairable if battery compartment is flooded. Housing cracks possible. Best avoided.
SB102:- Spares available. Very badly designed from a service point of view, can be very difficult to repair at the electronic component level. High voltage and low voltage circuit tracks are too close, so tends to die expensively from minor water ingress.
SB103:- warn Factory recall. Collector's item only. Due to a potential explosion hazard, Nikon recalled all SB103s and replaced them with the SB105. Replaced SB103s were rendered useless by drilling a hole in the case. Some of the drilled SB103s found their way back onto the secondhand market - caveat emptor!
SB104:- Discontinued 2002. Over-complicated design (Nitrogen filled housing, microcontroller-managed circuitry), weird battery pack. Reliable, but probably un-maintainable when Nikon support ceases.
SB105:- Replacement for the SB-103. Discontinued 2002. Well-designed small underwater flash. TTL reset too slow for digital cameras which use pre-flash.
Nikonos RS-AF:- Discontinued. Spares still available in 2003. Ludicrously expensive to refurbish if flooded.

D.W.K. 2006. 2012