What gives you a perfect exposure?

ISO ratings determine the image sensor’s sensitivity to light (these can go from 50 ISO right up to 100,000 ISO in the top end cameras), each rating represents a “stop” of light, and each increment (up or down) represents a doubling or halving of the sensor’s sensitivity to light. When changing the ISO, you normally have to select the ISO button then choose the desired setting.

The Aperture is set within the lens’ and controlled by the camera body, it is a diaphragm which controls the amount of light travelling through the lens to the camera sensor. When setting the aperture on the camera, it is done by numbers normally on top of the LCD screen moved by a roller or button, eg: 2.8 or 14.

The Shutter Speed indicates the speed in which the curtain opens then closes, and each shutter speed value also represents a “stop” of light. The shutter speed is measured in fractions of a second. Shutter speed shows up on the LCD also in numbers and normally looks like – 30″, 5″, 30, 80, 125, 1000.

When these three are combined, they represent a given exposure value (EV) for a given setting. A change in any one of these three will have a measurable and specific impact on how the remaining two react to expose the image sensor and how the image ultimately looks.

ISO (Click for large photo)

As you can see, the high ISO on the left (in this case, 12,800 ISO) causes a lot of digital noise making it soft compared to the 100 ISO as seen on the right, that is very clear and crisp. I never go over 400 ISO for model photography so the end result is perfect.

APERTURE (click for large photos)

A small f/stop number, ie; f/2.8 lets in a lot of light and also has a shallow depth of field (DOF), but a large f/stop number lets in less light and results in a deep DOF which means when shooting at f/14, like I do for model photography means a slower shutter speed to compensate. This is where using a tripod is a must to ensure a stead shot while the shutter is open, any movement will result in a blurred image, as seen below.

SHUTTER SPEED (click for large photos)

Two examples above show different shutter speeds, the top is 1/100th which is quite fast for use on a tripod and the lower photo I had the shutter open for 1 second. This is OK so long as you have a steady tripod, if you don’t you may get an image like the one above due to movement in the shutter causing the camera to move, always make sure that the tilt handle, panning arm etc are always firming locked/done up in place, otherwise shooting at slow speeds is usually fine on a tripod.

A good example; this was a 30 second exposure during a cold, windy night on RAF Northolt’s apron! (Click for large photo)



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