Wide-Angle Lenses

Blueboxx with dome port and dual strobes.

Wide-angle lenses should be used behind a dome port to maintain the angle of view and corner sharpness. The optics of a dome port is only working under water and therefore cannot be tested outside the water. Basically, the dome produces a virtual image on which the camera is focusing. As smaller the dome, as closer this image moves towards the lens.

Sharp images (especially in the corners) can only be obtained if the dome is large enough and the lens is able to focus close enough. What is enough depends very much on the lens and is difficult to calculate. In many cases the image quality can be improved by a diopter, however, with the diopter focus at infinity might not be possible any more.

I use an 8'' Ikelite dome port and port extensions from the Ikelite modular port system. The Ikelite port system is attached via a special adapter to the Fradotec housing. This dome port is quite large and the two Sigma lenses are able to focus without diopter.

Sigma 10 - 20 mm

For wide angle photography the Sigma 10–20 mm wide angle zoom lens is a good choice. To cover the wide angle, two Inon Z-240 strobes are used. I am quite pleased with the performance of this lens/port combination, especially with the sharpness in the corners. The sharpness is much better than with the combination Olympus C-7070/Inon UWL100 28AD. Off course, this comparison is not fair since with the UWL 100 I used the standard flat and not the optional dome port.

Sigma 17 - 70 Macro

Wide-angle lenses: Sigma 10-20 mm, Sigma 17-70 mm extended and with zoom ring.

Behind the dome port the whole zoom range of this lens (17 - 70 mm) can be used. Since this lens extends much more than the Sigma 10 - 20 mm, a port extender has to be used. Behind the dome port the close focus of this lens is a big advantage since it can be used without an additional diopter.

Behind a flat port the 17 - 70 is useful for fish photography and intermediate size objects. It is not (despite the name) a real macro lens since the maximum image size is 1:2.7 and not 1:1 as with true macro lenses. The flat port results in strong vignetting at focal lengths below 30 mm, and thus seriously limits the wide angle range of this lens/port combination.

Although the 17 - 70 is useful for underwater photography, it is a compromise at both the wide-angle and macro side. I prefer the Sigma 10 - 20 mm for wide-angle and the Nikkor 60 mm for fish photography.