Sports cameras / GoPro These cameras should not be bought for the purpose of dive photography. If you have one already or plan to use it mainly for other activities it might be a good thing to have instead of nothing, but they are not a reasonable investment for underwater photography. The fact that they normally operate only in wide angle, do not have any exposure settings etc, they are rather a minimum equipment for filming if you buy video lights with them.
Waterproof Compact Point-and-shoot without housing This is the minimum equipment. The camera does not extend the lens outside the case which makes them very compact. Those cameras are best used with automatic mode, offer very little control over the image produced but are relatively cheap, very small and do not require additional housing. The lack of external housing makes them most prone to flooding. There is usually no manual mode available which makes the optional external strobe not fully effective. The cameras are usually also rugged so can be used during many other outdoor activities without worrying that they get damaged. Further, these cameras often have a special underwater mode that makes colors in images with little/without flash look a bit better. Pros: Ultra-compact, low cost, versatile use for all kind of sports Cons: No upgrades, no external flash, no manual mode, no RAW image, lowest flood protection, low image quality, only down to 15 meters deep Best usage: Beginners or casual, infrequent divers who want to remember what they saw with snapshots but do not consider picture quality a priority. Example:Nikon Coolpix AW130 (ca 350 USD), Olympus TG-870 (ca 320 USD)
Compact Point-and-shoot Compared to the above waterproof point-and-shoot, those cameras are very similar but require an extra housing. If they have an expanding lens, the zoom and low-light capabilities are often better. So generally it can be said that you get a better image quality at the expense of the ruggedness, but the minimum price is lower (about 250 USD instead of 350) But here you need to invest into an external housing (around 300 USD). Optionally, you can get a waterproof model as above with an extra housing. This offers double water leakage protection, but also drives the price by about 100 USD. The biggest advantage is that you can invest into an external flash which will give you a much better picture quality than the above even for subjects further away. due to the lack of full manual controls, you cannot make 100% use of that flash however. Further, for the external flash you need more accessories such as mounting brackets. One huge bonus of some of the cameras available are special settings that are not available even on a DSLR such as the microscope mode in the Olympus TG series which are fantastic for macro images. Pro: Compact, Cost, full flash benefits, special image modes Cons: No Upgrades except external flash, medium/low image quality Best Usage: Divers who want to have a decent picture quality on a budget who want to shoot in automatic mode, special occasions (e.g. macro) Example:Nikon Coolpix S7000 (250 USD) with Ikelite Housing (350 USD) Waterproof with case: Olympus Tough TG-5 (ca 450 USD) with Ikelite Housing (ca 300 USD)
Advanced Point-and-Shoot Compared to the above Point-and-Shoot, those cameras are bigger, offer full manual controls and RAW shooting mode with a fixed lens. They have much better low-light & auto-focus capabilities, but still no real camera upgrade-capabilities due to the fixed lens. The fact that one has full manual controls however allows the full benefit of a better flash setup. The main reason to go for this level would be the full manual control and RAW image capabilities. The interesting cost factor is that the underwater housing is not much more expensive than for compact point-and-shoot cameras. The housing is also quite compact but even the camera would not fit into a small pocket anymore. Pro: Manual Control, RAW image, full flash benefits, cheap housing, compact Con: No upgrades for camera, basic understanding of photography required Best Usage: Beginners or casual infrequent divers who want a decent image quality and at least take full control of the lighting. Example:Canon Powershot G7X Mk II (700 USD) with Canon WP-DC55 Case (400 USD)
Mirrorless cameras Those are cameras with an interchangeable lens. There are generally 2 types: Those with maker-specific lens mounts and those with open-standard lens mounts. There are 2 open standards for lens mounts, Four-Thirds and Micro-Four thirds (more info here). While maker-specific cameras force you to buy lenses made by the same company as the camera, open-standard systems allow you to buy lenses for your camera from several different makers and therefore you have a wider choice. Since there are quite wide varieties in mirrorless cameras, prices, sizes and upgrade abilities also offer many different options. The big price differences however are caused mostly by the material of the housing (plastic or metal). The fact that you can use interchangeable lenses gives you a much better image control and quality as well as specialization for certain subjects. The price here has to consider additional cost for various lenses since the default lens normally does not offer very high image quality compared to what is possible with the available other lenses. Pro: Manual Control, RAW image, Interchangeable lenses, relatively compact Con: Housing becomes more expensive, needs more space Best Usage: Frequent diver with photography skills who want to be able to customize the setup for specific situations and have a really great but still portable camera for many different usages. Example:Olympus PEN Lite E-PL7 (550 USD) with Olympus PT-EP12 Housing (800 USD) and optional lenses (300-800 USD)
DSLR cameras DSLR cameras have a massive increase in size and costs compared to the above models. The more money you spend, one specializes for very specific usages (macro, wide-angle etc) which reduces flexibility but takes greater advantage of the maximum available increased image quality. One does not need to only buy a camera, a lens and a housing but also specialized domes for the lens currently used. The increased quality however allows to take great photos in challenging situations (e.g. fast fish in the distance) but also requires much better knowledge about photography to really benefit from the better equipment. Pro: Maximum quality and specialization possible Con: Very bulky, expensive, good knowledge required Best Usage: Semi/Professional photographers and frequent divers who want to possibly earn money with their photos. Example low price:Canon 100D + Ikelite housing (ca 1’650 USD) Example high price: Canon 5D MKIV w/o Lens (3’300 USD) + Nauticam Housing (3’800+ USD) + Lens