The Aperture

The Lens Aperture is one of the three components of the Exposure Triangle. The lensAperture is the hole through which the light travels on its way to the media whether it is Film or a Sensor (for Digital camera). While some lenses have a fixed Aperture (i.e. mirror lenses), meaning you cannot change the width of the hole, most lenses have what we call a diaphragm or an Iris. Just like your eye’s pupil, the lens Iris can expand wide open to capture as much light as possible (i.e. in dark environment) or reduce itself letting the tiniest beam of light through (i.e. in very bright situations).

The F-number

The width of the lensAperture is measured in F-number. Aperture is one of the most confusing settings for photography beginners and here is why: The smaller the F-number, the wider the lens opening is and subsequently, the bigger the F-number, the smaller the opening is. Here is the Aperture scale: f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64, etc. Most lenses would offer a range from f4 to f22 while some Luxurious lenses (i.e. Canon L Lens) would enable you do go down to f2.8 or even 1.4. You find wide Aperture in expensive lenses because the lenses need to be very wide to reach this opening width. For those of you who wonder where the F-number comes from here is the math behind it: Aperture = F/D   with F = Lens Focal Length* and D = the diameter of the entrance pupil. *The Focal lens length was covered in the post The Shutter when explaining the Blur phenomenon. When increasing or reducing the F-number to the next value, we refer to it as a full stop (just like for the ISO as seen in the ISO, and for the Shutter value as seen in the Shutter ).

Here are some sample exposures with only modified Aperture value

f4, 1/15sec
f4, 1/15sec
f5.6, 1/15sec
f5.6, 1/15sec
f8, 1/15sec
f8, 1/15sec
f11, 1/15sec
f11, 1/15sec
f16, 1/15sec
f16, 1/15sec
f22, 1/15sec
f22, 1/15sec
Some cameras will let you increment the Aperture value by a 1/2 stop or even 1/3 stop to give you more flexibility in your exposure. This is all there is to know about Aperture in an exposure.

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