In the first three parts of this series we went over each aspect of the Photographic Triangle: aperture, film speed (ISO) and shutter speeds. In part 4 I will show you how to use the 3 parts in conjunction in order to achieve the exposure you desire and master the art of metering you shots.
Aperture controls the size of the light opening.The lower the f/stop number the wider the opening. With a wider opening, your depth of field is decrease. Example:
Shutter speed controls how long the light opening is open for. The longer the opening is open the more light that it let in. The longest the shutter is open the more movement, or blur that can occur. Example:
ISO, or Film Speed is how sensitive the light collection material (digital sensor or Film) is to light. The higher the number the more grain that is incorporated in you photo. Example:
Let see how these relate but applying it to an earlier tutorial on the Sunny 16 rule. The sunny 16 rule states that in a sunny day set you camera to f/16 and set you shutter to the reciprocal, or 1 over, the iso speed. In our example we will use the settings f/16, iso 100, shutter 1/125. If we wanted to adjust these to sat open the aperture to shoot a bokeh type shot to say f/2.8 how in the world would we set the camera to keep it form over exposing? Remember that the more open the aperture is the more light that is left in.
An easy way to remember how to set you camera is this. If you adjust any of the 3 setting in the photographic triangle 1 stop, one of the other two remaining setting needs to be set in the same number of stops the other direction.
Using our sunny 16 example, f/16, iso 100, shutter 1/125, let start off easy and move the f/stop to f/8. as a result of this we either need to move the ISO to 50 or the shutter speed to 1/300. each ons stop in the “less light category. So since we want to fo to f/2.8, which is 4 stops form 16, keeping the ISO at 100, we should set the shutter speed to be 1/1000. This would give us the same exposure as the basic sunny 16 rule but with the added effect of the open aperture’s depth of field.
As a rule, I do not trust the auto settings on any camera to give me the exposure I need or want. For example, you may be trying to shoot a shot of a child running around. If you use the auto setting the camera does not know that your subject is moving and there for may select a shower shutter speed that will cause the subject to be blurry based on the amount of light. Also by giving up full control of the photo over to the camera will cause you to not be able to shoot Bokeh type shots, or portrait shots with the softer, blurrier back ground.
We now see that exposure is based on three factors: aperture, ISO and shutter speed. If you halve any of these, you must double another one to maintain an equivalent exposure. Also, besides this simple double/halve behavior, each of the four factors controls some secondary effect. aperture controls depth, ISO controls grain, and shutter time controls action.
*This is part of my series to introduce people to the world of photography. My hope is to help current DLSR camera owners to stop relying on the auto setting of their camera and unlocking the photographic potential of what they hold in their hand.
Richard Call is a Nashville, Tennessee based photographer whose work has been published locally as well as internationally and can be seen at richardcallphotography.com
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