Effective photography appears to be very much a balancing act: the inter-relationship between ISO(International Standardisation Organisation), aperture and shutter speed. Some helpful tools which shed some illumination on the 'light issue' are:
1. An 'Available Light Exposure Calculator' - enter the photographic conditions using a drop down menu . It claims:
Enter a film speed (or digital equivalent) and ambient lighting conditions. We will give you a table of apertures (f/stop) and shutter speed for the given exposure value (EV). This table allows you to use a camera with manual control in conditions outside the range of the built-in light meter, which is common in available light photography. The table does not account for reciprocity failure which reduces the sensitivity of film for very long exposures (this does not apply to digital sensors).2. Aperture and shutter speeds based on film speed for many conditions ( you need to scroll down the page to locate the table)
4. Select the aperture, shutterspeed, and ISO in the interactive EV calculator below, and click on the "Calculate EV" button to determine the corresponding exposure value.
5. A great video from my new tutorial hero 'Jay from JayHP' Video Tutorials