First of all, we must know what P mode? Your camera is blind to the world and we must make many assumptions about this DSLR camera, including how many lights out there, where to focus, how fast the subject is moving and the ideal depth of field (or how much in front of and behind the subject should be the focus for example 2 meters in front of and behind the subject or. as much as possible). Switch the camera to P mode means the camera to make the best ‘guestimate’ It could be for all of the unknown.
Why is the amount of light that are important for your camera? Think of your own eyelids and how each of your eyes have iris. When it was a very sunny day you tend to squint and expand your iris to protect your retina. Conversely, in a dim room, You open your eyes as wide as possible and iris.
Iris eyes are the eyes and eyelids due to varying amounts of light retinas like a certain amount of light to register the information that we see too little light and your eye sees only limited information, too much light and your retina is overloaded and you see nothing.
Your camera sensor is the equivalent of your eyes the retina where the light of information about listed, and just like your retina, then the ideal sensor DSLR like the light quantity. Unlike your eyes, Your camera does not have eyelids or iris to regulate the amount of light. Instead of light with the camera control varying the shutter speed and exposure.
Two new terms, shutter speed and aperture, deserve an explanation. Think of a shutter as a primitive eyelid for your camera, primitive in that the shutter is either open or closed and cannot be anything in-between. When you take a photo, the shutter temporarily retracts so light can come through the lens and register on your camera’s sensor. The longer the shutter retracts, the more light hits the sensor. In a bright room, you only want the shutter to retract for a short time or the sensor will be overloaded. In a dark room, you want the shutter to retract for much longer to give your camera’s sensor enough time to register the far dimmer light. The typical shutter speed is 1/125th sec which means the shutter temporarily retracts for a tiny fraction of a second but most DSLRs’ shutter speed ranges from 30 seconds to 1/4000th of a second. A later article in this series will later explain why you would want to vary shutter speed.
Now you know what a shutter does, where does aperture fit in? The aperture is the iris of your camera. It is physically part of your camera’s lens, it is usually octagonal and it restricts light by expanding and contracting.
Unlike an iris, an aperture has a ratings system e.g. f5.6, f8, f11. What does this mean? The ‘f stop’ rating simply explains how much light is let in by the aperture using a scale where f2 lets twice as much light as f4 as f5.6 lets twice as much light as f8 which lets in twice as much light as f11…. This is a confusing scale – just remember, the smaller the aperture (e.g. f4 instead of f 11), the more light is let in.
In summary, a DSLR controls how much light registers on the camera’s sensor by varying the size of the aperture and by varying the time the shutter retracts. It stands to reason that different combinations of shutter speed and aperture will result in the same amount of light reaching the sensor.
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