Digital Underwater Photography

Reflexes are cameras with a viewfinder system composed of a mirror and a pentaprism: the image formed on the sensor and on the viewfinder is the same as the one that would be seen through the lens. With analog cameras this technology would strongly differentiate the viewing system with respect to non-reflex cameras, which mounted a separate viewfinder. In digital cameras this difference is largely overcome by the use of the LCD display.

Of course, shooting with a reflex is an altogether different experience, but apart from this, the fundamental differences with respect to the other categories are the larger sensor size, the range of interchangeable lenses, and the possibility of total control over image parameters. Another key feature of reflexes is operating speed: basically, there is no appreciable shooting delay and focusing is almost instant. On the other hand, they are larger and heavier.

A new category of cameras in between hybrid and reflex is under development: they show a more compact body, as there is no mirror nor pentaprism, substituted by an integrated electronic viewfinder, not an add-on like in hybrid cameras. This new category will be included in the reflex class.

Underwater housings for reflexes always mount interchangeable ports to allow for the use of different lenses and cable connections with an external strobe. These can be occasionally triggered by an optical link with the on-camera strobe. In general, reflex housings are dedicated to a single model, with some exceptions.

The main technical characteristics for underwater usage are:

Availability of underwater housing: indispensable, of course.

Max operating depth: depends not only on housing resistance, but also on operability of buttons at high hydrostatic pressure.

Dedicated housing: the housing may be built for a single model, or for different models: in the latter case it can be reused, following technological advances.

Material: housings come in different materials, mainly aluminum and polycarbonate. The choice of the material affects robustness and weight: a sturdier casing may turn out to be too heavy, and viceversa.

Additional lens for the viewfinder: some housings can attach a lens mount to the viewfinder to improve viewing.

Sensor size: with equal megapixel number, a larger sensor ensures a higher signal-to-noise ratio, and therefore a better image quality.

Megapixels: a higher number of pixels is not necessarily a synonym of better quality, which instead

is mainly related to individual pixel dimensions.

Viewfinder: can either be the traditional reflex system, or electronic, for cameras without mirror and pentaprism.

Interchangeable optics: the wider the lens choice range, the higher the camera versatility.

Wideangle: availability of fixed or zoom wideangle lenses is fundamental to landscape photography.

Macro: the minimum focusing distance in macro mode, expressed in cm, gives a measure of the quality of small subject images; in addition, the minimum focusing distance in tele mode is also important because the strobe light diffusion is more uniform at not-too-close distances.

Stabilizer: very useful because cameras tend to select long exposure times underwater with ISO not too high (high ISO's are not recommended for good image quality).

Sensor size: at equal megapixel number, a larger sensor ensures a higher signal-to-noise ratio, and therefore a better image quality.

Wide-angle zoom: rather than the focal range of the lens (usage in tele position is very limited), what really makes a difference is the minimal focal length (expressed in mm as 24x36 focal equivalent), providing as wide as possible a view angle.

Display dimensions: in inches: the larger the viewer the easier is subject framing. Visibility in strong light conditions is also important; quality depends also on resolution, in dots per inch.

Live view: on some cameras the display can be used as a viewfinder, like on compacts. In general this may cause operational limitations in focusing and/or exposure adjustment. It is useful when using a tripod with still subjects.

HD video: ensures better video quality.

Trigger/strobe dialog: the complex electronics of reflex cameras does not always allow for a TTL dialog between strobe and camera, and this affects underwater operating speed.

Price: in US dollars "from"; should be assessed considering both camera features and total price, housing included.