Beginner's Guide to Photography e-bog

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. It is quite impossible to write down anything definite with regard to the length of time for which the lens must be uncovered. If we had only one particular subject to photograph, and this subject were always lighted by the same amount of daylight, it would be an easy matter to calculate the amount of exposure required with every diaphragm of a lens, provided that the necessary amount had been ascertained by experiment with but one of those diaphragms. For these stops or diaphragms, as furnished with modern lenses, have apertures bearing a definite relation to one another. As a general rule each diaphragm will require double the exposure needed for the next size larger. Or to put it in another way - suppose the smallest stop of a lens to require an exposure of 24. Seconds with a given subject, with the next size larger the exposure will be 12, then 6, then 3, then until we come to the full aperture of the lens, by which the picture can be taken in ofa second. But as a matter of fact, the exposure varies not only with the nature of the subject, but with the time of day, the time of year, and the state of the atmosphere. The old adage, Experientia can not be more aptly quoted than in connection with this question of exposure.