Equivalent Exposures handout

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Equivalent Exposures handout Powered By Docstoc
					Ted Hewitt                           Introduction to Photography                                    Photo 8

                                         EQUIVALENT EXPOSURES

Read pp. 76-81 (More on Exposures); and pp. 96-99 (Evaluating your Negatives)

    Exposure is determined by:
        the lens aperture (f-stop setting–controls the amount of light entering the camera)
        the camera shutter speed (controls the duration of light entering the camera)
        the sensitivity of the film to light (ISO/ASA value)
        the intensity of the light that illuminates the subject

    This handout addresses aperture and shutter speed.

    We know instinctively that it will be necessary to alter the camera settings when we go from bright
light to dim light. That is, we know that there is only one correct exposure for a given set of lighting
conditions. However there are a large number of different combinations of camera settings that will yield
this one correct exposure. In other words it is possible (and often desirable) to alter the camera settings
without altering the exposure.

     For example, if you were using T-MAX 100 film on a bright, sunny day, your light meter should
read very close to f/11 @ 1/250. But depending upon the “priority” of your camera (aperture-preferred,
shutter-preferred, or perhaps “program”) you might find that your light meter reads f/16 @ 1/125. That
is, by cutting in half the amount of light that passes through the lens iris while doubling the interval that
the shutter is open, you would still have a well-exposed frame of film. Similarly, f/8 @ 1/500 would also
produce a well-exposed film. The following diagram presents this concept in a different fashion:

   FIRST, you must determine one correct exposure using your camera's light meter. All the other
exposures will be calculated from that reading. The diagram below shows many different "correct"
exposures based on a single light meter reading of f/16 @125th of a second

The light transmitted by the lens doubles with each full-stop increase in the aperture setting.

                                    (These numbers are for example only.)
Under different lighting conditions, a different exposure would be needed. For example, on a dull,
overcast day with no shadows, your light meter would likely read something close to f/5.6 @ 1/125. But
any of the other combinations shown in the following chart would also yield well-exposed negatives
under this set of lighting conditions.

                               (These numbers are for example only.)

For this assignment, you will make at least five different photos using five different f-stops. FIRST,
use your light meter to determine one good exposure setting. Then, when you change f:stops, ALSO
change shutter speeds! Each image should be properly exposed.

                                                                               Use full f-stops.
                                                                               For example:

                                                                               f/5.6 @500th/sec
                                                                               f/8 @ 250th/sec
                                                                               f/11 @ 125/sec
                                                                               f/16 @ 60th/sec
                                                                               f/22 @ 30th/sec

Photos by Kaitlyn Starner

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