Under Water Photograph
In the beginning years of under water photography, the medium format (60mm square) was the preferred choice. Armed with Hasselblad and Rolleiflex cameras, our pioneers opened up the under water world. But these cameras were large, and suffered from a lack of depth of field (about four times worse than 35mm cameras). As film emulsions improved, the field was taken by the small format (35mm frame) cameras.
Because under water photography is best in close-up, depth of field is very important. Resolution can be attained by using low speed film and longer exposure times or by resorting to negative film.
Whereas progress in film emulsion technology has been slow, progress in electronic imaging has been rapid. Cameras now claim as many as 6 million pixels per image (a scanned 35mm Kodak Photo-CD image has 3000x2000 = 6 million pixels, compressed to some 6MB, about 80 lines per mm, the resolution of most slide films)
Digital images show the result immediately, allowing for on-the-spot improvements to lighting, exposure and even contrast. Digital cameras are more sensitive, being able to take pictures in low light conditions. The CCD (Charge-Coupled Device) is small, allowing for short focal lenses with vastly superior depth of field characteristics. Very recent digital cameras now provide resolutions comparable to the 35mm frame.
For the amateur under water photographer who wants immediate results that can be reproduced professionally up to sizes of 100mm across, the digital camera is the solution. In the past few years digital video has stormed the world, providing superior pictures that can be obtained with ease. The digital colours of 3-CCD cameras are 'additive' as opposed to the 'subtractive' colours of slides and negatives, making a whole new range of 'fluorescing' intensive colours available. Unfortunately these can not be rendered in print. Most still digital cameras, however, use a single CCD colour technique which renders colours subtractive. The most standard method of saving the image, is in the standardised sRGB (scanner-Red-Green-Blue) computer format, which prints beautifully, the way one sees it on the computer screen.
The digital image is made up of (square) pixels, each containing three colours, red, blue and green, much the way a television image is composed. Each colour can assume only discrete values, ranging from 0 to 255. At mid-exposure of 150 units, a picture looks rather dark whereas a one stop over exposure (2 times) at this point would overexpose the image to 300 units, which is 'clipped' not to exceed the value of 255. So working with a digital pictures can be even more critical than working with slides.
Fortunately, the high quality end of the digital cameras produce images with 10 or even 12 bits colour depth, thereby extending the range considerably (from 255 steps to 4096). But the JPEG compressed file format has only 8 bit precision.