Every photographer has at some time produced a photograph with a technical fault. Literally hundreds of faults are possible in a process of such chemical and physical complexity, and whole books have been written about nothing else. With the automation of exposure and, to a large extent, processing, added to the manufacturers' continual quest for more robust materials, faulty images have become less frequent; but they can and do still occur. They fall into three general categories: unsharpness; incorrect density and contrast; and artefacts, i.e. marks, fogging, and discoloration. The lists and tables below indicate the most common faults, their causes, and (where possible) remedial action.
Unsharpness
There are three basic causes of unsharpness in a photograph:
• Incorrect focus. The image is blurred uniformly, with no fine detail visible. In a negative or transparency, some parts of the scene may appear sharper than others. This can happen even with autofocus systems, especially in close-ups. Use the correct
• Camera shake. The image is blurred in one specific direction, so that points appear as short lines. Fine detail may be doubled. The shortest feasible exposure should be used, even if it means using full aperture, unless the camera can be held steady on a firm base. Moving subjects can be followed by panning the camera. In printing, the enlarger should be operated with a remote switch.
• Dirty optics. The image is low contrast and hazy, but fine detail is present. Optical surfaces should not be touched, and a lens tissue should be kept handy.
Incorrect density and contrast
The table below assumes that the film is fresh and the processing solutions have been correctly prepared. It does not apply to transparencies or prints.
Exposure errors in transparencies can usually be compensated for, if known before processing. Underexposure of up to two stops can be remedied by extending the first development time by up to 50 per cent (push processing), overexposure of up to one stop by reducing it by up to 20 per cent. Pushing the development results in some loss of colour saturation. Small exposure errors in both monochrome and colour prints can be compensated for by adjusting the development time, within certain limits.
Artefacts
An artefact is any fault that produces a photographic image where no optical image existed. The list below does not include optical quirks such as lens flare spots and ghost images, which can be avoided by the use of a lens hood and a careful choice of viewpoint, but there are still hundreds of possible causes of artefacts. In their diagnosis it may be prudent to follow the legendary principle of Sherlock Holmes: ‘Once you have eliminated the impossible, what remains, however improbable, must be the truth.’ The most common problems in negatives and transparencies are tabulated below.
Faults in prints
Almost all the faults that occur in negatives can also occur in print materials. Faults in colour prints are usually confined to colour casts due to incorrect CP filtering of the enlarger light. A colour cast in the shadows only is usually the result of underexposure of the negative; but if the negative was correctly exposed and the print shows colour casts in opposite senses in the highlights and shadows, the film was probably stale or imperfectly stored. In both cases correction is possible only by digital manipulation of the image. In monochrome prints the most common faults are as shown in the table above.
— Graham Saxby
Bibliography
- Life Library of Photography: Special Problems (1972).
- Jacobson, R. E. (ed.), The Manual of Photography (9th edn. 2000)
