In my first post I disclosed the different types of exposure meters built in our cameras and I also discussed briefly how incident meters read the light. I will review today apertures and shutter speeds as they work to make an exposure. I will assume you have some basic knowledge about these two important camera settings. If you do not, I refer you to the many books available on this subject. Apertures are "holes" made in the lens by the settings of apertures in camera or lens and it is a function of the diaphragm. They control the amount of light entering the camera. A regular set of apertures for a f1.4 lens would be something like f1.4, 2, 2.8, 4, 5.6, 8, 11 and 16. The higher numbers, like f16 are small lens holes while the smaller numbers, like f4 are large holes. Apertures are used creatively to control depth of field. Shutter speeds control the time during which the light enters the camera. A set of shutter speeds could look like this: 1sec., 1/2 , 1/4. 1/8, 1/15, 1/30, 1/60, 1/125, 1/250. 1/500 and 1/1000. The shutter speeds, when using flash control ambient light. They are used creatively to control motion. Apertures and shutter speeds work in half or doubles. An example, f8 accepts only half the amount of light used by f5.6 but double the light of f11. Look at the holes in the lens and you will see why. Same thing for shutter speeds so that 1/60sec. is twice the time of 1/125 but only half the time of 1/30. In photography meter readings give you a combination of shutter speed and lens opening to form the exposure. That combination is not necessarily what you have to use; you could use other combinations and still the same amount of light reaches the film or the digital sensor. An example: f11-1/60sec. is exactly the same exposure as using f16-1/30 or f22-1/15sec. Same exposure as using f8-1/125, f5.6-1/250 or even f4-1/500sec. Notice that if the aperture gets larger the shutter speed gets faster and viceversa. This is universally known as RECIPROCITY. Obviously, modern cameras set shutter speeds and apertures with camera controls but with manual cameras of the past we had to set apertures in the lens and shutter speeds in camera. Modern cameras can set values to 1/3 stop when necessary and if you do not know what a stop is it is exactly the difference between one shutter speed and the next or the aperture set in your lens and the next one. Stops are universally designated with an f in front of the aperture in use, for example f8. I hope I have not confused you but this is all basic photography. In my next post I will show you how to use your camera meter for consistent exposures. Till then. William Rodriguez Miami, Florida.