Being in a position to present the images displayed on this site has been a photographic journey through time and space. The equipment is only one side of the story.
A good knowledge of the behaviour of the subjects, the environment, light, perfect bouyancy control and a very large measure of patience is perhaps more important than the equipment. Without this, no camera is going produce good photographs.
Small format cameras can produce good macro images, but are usually challenged with large subjects and wide angle shots. One of the disadvantages here is that the camera needs to get fairly close to the subject, and without an external flash, the internal flash is aimed directly at the subject. This can be traumatic for the subject, and back-scatter from suspended particles can render the image useless. The use of an external flash allows indirect light to be used, avoiding these issues. A few of the early images here were taken with a Canon G9 in a Patima housing with an Inon Z240 external flash.
Most images however were taken with a Nikon D750 in a Seacam housing with Seacam 100Digital strobes. Macro/super-macro and fish portraits were mostly taken with a Nikkor 105mm 1:2.8G objective; wide-angle with an AF-S Nikkor 16-35mm 1:4G objective; and super fish-eye with a Sigma EXDG Fisheye 15mm 1:2.8 with a Kenko N-AF 1.4X Teleplus Pro 300
Super fish-eye photography was first used in underwater archaeology in the UK. High sediment loads in the water made normal photography all but impossible. With super fish-eye, the subject is almost touching the glass of the micro-dome port, so there is almost no water (i.e. no sediment) between the subject and the objective. It has the added advantage of giving images with a high depth of field (only realised in good visibility of course). Lighting is not simple, but as always, indirect lighting (strobes conservatively set) gives the best results. Only subjects that cannot be damaged or impacted by this type of photography should be attempted (e.g. sea fans, corals, starfish, anenomes).