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WCON-07C Wide Converter for C-5050 and C-7070.
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| In normal underwater practice, use of a lens having a 35mm equivalent focal length of much less than 35mm behind a flat port is considered to be poor practice. With the PPO-02 and WCON-07C however, we have the equivalent of a 19mm lens behind a flat port, a combination so bad that chromatic aberration is even visible in the uncorrected 273x205 pixel thumbnail image below. Faced with the paradox of how to market this device and still retain some semblance of public credibility, the author decided to investigate the possibility of applying radial correction to the camera output files as a way of producing acceptable images. This investigation forms one thread of the radial correction article given elsewhere. If images are corrected according to the instructions given in that article, the results can be excellent. On the other hand, those who are not prepared to apply radial correction should avoid this port and use the Ikelite housing and dome port instead.. |
 Geometry before correction. |
 After correction. |
 Corner detail before correction. |
 Corner detail after correction. |
| Panorama Tools radial correction coefficients for the maximum wide-angle zoom setting: |
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# 6130.61 (fitted with standard port). 
Screw-fit interchangeable ports. Optional dome port.
67mm filter thread on standard port.
TTL flash via cable with optional DS-series Substrobes.
Internal flash can be used underwater with standard port. Housing
includes diffuser.
All camera functions are accessible.
Depth rating: 60m |
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#9306.37 High
precision injection moulded acrylic optical dome. Optical data: Port material: Acrylic, nD=1.492. Inside radius: 3", 76.2mm. Nominal thickness: 0.218", 5.537mm.
True 97° wide-angle (wider than the Nikonos 15mm):
Dome port preserves the 97° coverage of the Olympus WCON-07C
conversion lens underwater.
Gives 73° coverage when used without the wide-converter
lens.
Two-part lens housing holds the conversion lens without the need
for the Olympus CLA-7 adapter tube - allows the camera to be
removed and installed without disturbing the port. |
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Olympus WCON-07C wide-converter: Magnification (focal length multiplier): 0.7x In-air coverage: 97° max with C-5060 or C-7070 camera and CLA-7 adapter tube (equivalent to 19mm lens in 35mm format).  The CLA-7 adapter tube is required for attachment
of the WCON-07C to the C-5060 when using the camera without the
underwater housing. |
 CLA-7 |
 WCON-07C in air (no port). |
 WCON-07C with DP-60 dome, underwater. |
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Shooting information: zoom setting: 5.7mm (35mm equiv: 27mm). Effective air focal length with WCON-07C: 19mm. Angle of coverage UW: 97° nominal. Aperture: f/8. Focusing mode: Macro. Distance: Object plane to entrance pupil: 337mm perpendicular, 509mm at L/R edge of field (calculated). Object plane to outside of dome: 256mm perpendicular, 427mm at edge of field (nominal, calculated). |
 Full resolution corner detail. |
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The first point to notice is that the Ikelite DP-60 dome-port
introduces no additional geometric distortion beyond that which
is characteristic of the WCON-07C and camera. Mild fisheye distortion
is apparent but this is normal for wide-angle lenses. The chromatic
aberration visible in the corner detail is a consequence of the
air-water boundary and is not an optical defect of the dome.
The system exhibits excellent overall image sharpness. Slight
softening of focus at extreme edges is due to large difference
in lens to subject distance between centre and edge (curvature
of field) - see shooting information above. The effect will be
reduced for larger object to camera distances. This optical system gives truly outstanding performance for its class. Optical correction is not necessary for normal display purposes, but due to the narrow spectral bandwidth of the RGB sampling system used in the C-5060 camera (and Bayer mosaic sensors in general) and the well designed Bayer to RGB interpolation algorithm used by Olympus, it is easy to determine a near-perfect compensation for chromatic aberration and thereby obtain the performance of a fully water-corrected lens. Large high-quality prints are then possible. The effect of radial correction using Panorama Tools is shown below: |
 WCON-07C + DP60, after correction |
 full resolution corner detail |
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The PanoTools radial correction coefficients which were used
are shown right: → These coefficients will correct all pictures taken with the C-5060 + WCON-07C + DP60 underwater with the zoom set at full wide. |
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Above left: bare camera lens in air (no port), full wide. Above right: bare camera lens with DP-60 dome port underwater, full wide. Right: full resolution corner detail. Shooting information: zoom setting: 5.7mm (35mm equiv: 27mm). Angle of coverage: Air: 77° nominal, Underwater: 73° effective (measured 73.4±1.1°). Aperture: f/8. Focusing mode: Normal AF, with assistance from spotting light in Ikelite DS-125 Substrobe. |
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| The DP60 dome port works perfectly well underwater without the WCON-07C installed and very nearly preserves the 77° coverage of the camera lens underwater. Actual coverage was 73.4±1.1° at a lens pupil to subject distance of 0.75m. This lens+port combination therefore exceeds the coverage of the Olympus PPO-02 flat port with the WCON-07C (68°), and gives vastly less optical distortion. The prototype dome port tested gave very slight vignetting at the corners of the picture, but this was corrected in production versions by slight adjustment of the port-shade cutouts. Also, software radial correction pushes the vignette out of the picture. Chromatic aberration at this angle of coverage with the Ikelite port is negligible (the green-magenta fringing in the detail above is actually due to the zoom lens), but radial correction for the barrel distortion introduced by the zoom lens is beneficial. The corrected underwater image is shown below: |
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The PanoTools radial correction coefficients which were used
are shown right: → These coefficients will correct all pictures taken with the C-5060 + DP60 underwater with the zoom set at full wide. |
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Camera internal flash is obscured (but can trigger slave flash).