Retina wrote:
I never heard of the triangle. Is it like a tripod for long exposures? Forgive me, I am a newcomer and only recently learned that the word lens is obsolete and was replaced by the term "glass" years ago. It takes a while to get used to this digital stuff. I was really happy to learn that you can set sensitivity AFTER loading a new memory card so all the pictures I take have a better chance. At least I know why the cashier looked at me funny when I ask for an ASA 400 card. So what is the triangle, anyway?
I never heard of the triangle. Is it like a tripod... (
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Welcome to the 'hog. The EXPOSURE triangle is the relationship between
aperture (volume of light coming through the diaphragm in the lens),
shutter speed (length of time of the exposure), and
sensitivity measured by ISO (pronounced EYESO in the USA, EEESO in most of the rest of the world, not an acronym but the proper name of the International Organization for Standardization).
For a given sensitivity setting (ISO) there is a FIXED amount of light which will create a proper exposure of a scene. Proper exposure is subject to interpretation and post-photography processing manipulation.
Adjusting the shutter, aperture, and ISO controls on your camera is what balances these points of the triangle around the available illumination. More light allows faster shutter speeds, and/or smaller apertures, and/or lower ISO. Less light requires longer/slower shutter speeds, and/or wider apertures, and/or higher ISO. Again, all three points of the triangle must be IN BALANCE with the amount of light you have, or will use, to make the exposure. You cannot adjust one without adjusting at least one of the others. Failure to adjust means the scene is underexposed (too dark) or overexposed (too light).
Camera automation attempts to do this for you. HOWEVER, since the light meter in the camera is calibrated for an average scene reflectance between 12% and 18% (which is correct is the subject of much conjecture and argument here), if you use automation on a black cat in a coal bin, the scene will come out GRAY. If you use automation on a white, blonde bride in a white dress against a white wall, the scene will come out GRAY. Manual exposure methods rely on metering knowledge, test targets, experience, exposure compensation settings... all sorts of methods to compensate for the dumb meter reading.
Most modern cameras have some attempt at "intelligent" metering patterns built into them, but all may be fooled under certain circumstances.