Monochrome images
Negative (Left) &
Positive (Right)
Colour images
Negative (Left) &
Positive (Right)
A SIMPLE GUIDE TO PHOTOGRAPHY.
1. Chemistry and Photography.
Conventional photography is possible only because certain chemicals are affected by light, and change their chemical composition. Compounds of silver, especially the bromide, AgBr, are often used in films and photographic printing papers. The camera lens projects an image on to a film inside the camera, and the intensity of light on each part of the image determines the extent of the chemical reaction. The film must then be processed to remove the unaffected portions of chemicals and to stabilise (fix) the reaction products onto the base material.
Black and white photography is usually performed in two stages. First, a negative image is produced, and from this, a positive print is produced by projecting the negative image onto photographic paper coated with light-sensitive chemicals. The paper is then processed using suitable chemicals to produce a black and white (monochrome) print.
Colour prints are produced in a similar manner to black and white prints via a 2-stage process - film to negative, then negative to print, but the chemistry is more complicated, dyes or pigments being present in the film.
Colour slides (transparencies) do not involve use of the intermediate change of producing a negative. Instead, a positive image is formed on a transparent plastic material. It is also possible to produce prints from slides.
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Monochrome images Negative (Left) & Positive (Right) |
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Colour images Negative (Left) & Positive (Right) |
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If you want to read more about the chemistry of films and processing, these sites contain much information (but you may find some irritating pop-up adverts.):
www.cameradocs.com/photochem.shmtl
2. Digital Photography.
This has considerable similarities to chemical photography, except the light falls onto special types of chemical sensors (most commonly Charge Coupled Diodes, or CCD's) that convert light into an electrical signal. The camera contains a processor - effectively a type of computer - which converts the signal into a digital file containing all the information about the photograph - principally the light intensity and colours. The sensors consist of large numbers of pixels (picture cells). Increasing the number of pixels increases the resolution (sharpness) of the photographs, assuming that the camera lens does not degrade the image. If you want to produce large prints, then you will need a camera containing at least 4 mega pixels.
Currently, digital cameras cost 3 to 4 times more than conventional (film) cameras if you want to produce prints of equal quality. The site below gives a lot more information on digital cameras and their technology.
www.digicaminfo.com/index.html
3. Digital Scanners.
These devices are used to scan either prints or slides, and produce a digital image file in a similar manner to digital cameras. Flat bed scanners - similar in layout to photocopiers - can scan prints, and with the addition of an adaptor containing a light source, they can be used to scan film slides or negatives. Special scanners devoted for use with film slides or negatives generally give the best quality images, but are more expensive than flat bed scanners. Scanner resolutions are expressed as "dots per inch". A high resolution scanner gives better quality images, but at the expense of slower scan times and large image file sizes.
The site compiler uses a conventional film camera, with Kodachrome 200 slide film - I would prefer to use Kodachrome 64,which I think gives better colour reproduction, but it is too slow to use for fast-moving trains, especially when the lighting conditions are dull. For use on the site, slides are scanned using a flat bed scanner with slide adaptor, operating at 1200 dots per inch resolution.
Having produced an image file, digital processing is used to produce the final result. Please continue to the next page for more details.
Goto Digital Image Editing Page.
Links to Photography Sites.
A wide range of photographic sites - both technical and photo. displays, can be accessed via
www.cameradocs.com/links/Site_Links.html
The Lancashire & Cheshire Photographic Union Site also contains lists of clubs in this area, if you wish to join your local camera / photographic club.
The fixtures and location of my local club, St. Helens Camera Club, are available at
This page compiled by Bevan Price on 16 January 2004