Please explain me this

Started Feb 11, 2013 | Discussions thread
PicOne
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Re: Please explain me this
In reply to hea, Feb 12, 2013

hea wrote:

Darrell Spreen wrote:

You described your question as a technical question. I think you may be asking why the image doesn't become dark at the edges when you close the aperture -- giving a narrower image.

The aperture in a lens is placed at a very precise spot inside the lens which is called the nodal point. It's a place where all the light rays entering the lens come to a point before expanding again to illuminate the sensor. With the aperture at that point, its only effect is to limit the amount of light coming through the lens and it does not "clip" the image.

When the aperture becomes very small, however, it does result in diffraction (which is actually a wave-optics phenomenon) and the light rays will not be as precisely focussed on the sensor as they are with a larger aperture. Many people avoid shooting with very small apertures, if possible, to avoid what are called diffraction losses.

I hope I understood your question correctly.

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Darrell

yes, this is what I was asking about, how is that closing the aperture (a hole i think) dont change the field of view (what I call the scene or composition) thanks

Lenses are curved.  When aperture is widest, all parts of the lens are used to project the scene thru the big hole.  When the hole is smaller, less of the lens is used to project the scene thru the hole so less overall light is hitting sensor.

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'Everything in photography boils down to what's sharp and what's fuzzy.'
-Gaylord Herron

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