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Aperture

January 28, 2010 Comments off

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The Aperture, or lens opening, is one of the controls you have in your DSLR camera to adjust how much light gets to the digital sensor/film in your camera.
The Aperture settings or fstops are shown in your viewfinder ranging anywhere from

f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32
Most cameras come with a 50mm lens that will range from about f2 to f/16.


The lower the fstop number the wider the lens opening.
The higher the fstop number the smaller the lens opening.
So going from f/11 to f/8 lets in twice as much light, while ‘stopping’ down from f/11 to f/16 lets in half as much light.

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If you do not have an Aperture ring on your lens then you will have to control your Aperture through your viewfinder.
First set your camera to Aperture Priority Mode.

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Then depending on your camera use your dial to adjust your aperture.  Your current aperture (fstop) will be displayed in your viewfinder and on the LCD panel.  In the image below the aperture is f/4.5

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You can therefore use your Aperture to control how much light comes into the scene, and more importantly, you can use your aperture to control the depth of field of your shot.  Or how much of your photograph is sharp.  Large depth of field means most or all of your photograph is in focus, small depth of field means only a small part of your photograph is in focus.

As aperture opening gets smaller, your depth of field increases and more of the scene from near to far is sharp. The image below was shot at f/32

As your aperture opening gets larger your depth of field decreases and less of the scene from near to far is sharp.  The image below was shot at f/5

*Larger openings have smaller numbers because the f/number is a ration of the lens focal length divided by the diameter of the lens opening.

So this lens has a 50mm Focal Length, a lenses focal length determines how wide of a view the lens will shoot.  The longer the focal length the narrower the view.

1:2  is this lenses maximum aperture shown as a ration of 1:2, This lenses maximum aperture then is f/2

Notice the small triangle with the number 49mm, this is the filter size, it is also the diameter in mm of the lens.

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***Most lenses have a sweet spot, a certain aperture where the lens takes the sharpest image it will take.  For the most part that aperture is 2 stops above the lowest aperture the lens has.  For the lens below its sweet spot would be at aperture f/4.  Keep this in mind if you are shooting landscapes and want everything in focus***

This brings us to lenses, without getting too much into lenses and focal lengths  and sensor sizes, most Digital SLR’s come with a zoom lens with a focal length range of about 18mm to 55mm.   You can find this on the zoom ring of your lens.   Most commercial DSLR’s come with an APS-C size sensor.  This means that to get the traditional 35mm film equivalent focal length, your lenses focal length has to be multiplied by 1.6 so that y our 18mm to 55mm lens is actually a 28.8mm to 88mm lens.  But this is mostly technical.

What you need to consider is that the shorter your focal length the wider your angle of view.  So that when shooting landscapes if you want to view the entire landscape shoot at the lowest focal lenght and if you want to zoom in, go higher focal length lens.  However, notice that as your focal length increases your image appears flatter.  Your angle of view narrows and the size of objects increases and the distance between objects in your scene appears to be smaller and smaller.

Categories: Aperture