How does an aperature even work?

Posted on March 14th, 2010 by webmaster
  • How come when you make the aperature smaller such as F/22 its like the size of a dull pencil tip., but none of the picture gets cut off? As opposed to F/1.4 where its huge.

    Is there a diagram anywhere of how an aperature actually affects the light? and whatnot?


  • I like the analogy that I once read using water. Poor a small stream of water into a shallow bucket and the water will fall nicely into the bucket (small aperture). Dump another bucket of water rapidly into that shallow bucket and the water will splash everywhere (large aperture).

    Or something like that...


  • a) Its aperture (sorry, grammar Nazi).
    b)http://www.mir.com.my/rb/photography/fototech/apershutter/aperture.htm


    This has nothing to do with aperture, since it has already been answered sufficiently...

    I just found this funny: grammar Nazi? Then it should be

    "It's aperture." (with an apostrophe)


  • a) Its aperture (sorry, grammar Nazi).
    b)http://www.mir.com.my/rb/photography/fototech/apershutter/aperture.htm (long read).
    c) http://www.photoaficionado.com/equipment_photos/macro/aperture_diagram.jpg

    d) http://www.great-landscape-photography.com/image-files/depthoffield.gif

    Basically, the image registered does not change size, because that is determined by the lens size/shape and the sensor/film. The aperture just limits the amount of light that hits the image.


  • I like the analogy that I once read using water. Poor a small stream of water into a shallow bucket and the water will fall nicely into the bucket (small aperture). Dump another bucket of water rapidly into that shallow bucket and the water will splash everywhere (large aperture).

    Or something like that...

    There is a quote similar to that in Understanding Exposure. Peterson explains it like this: Think of light as a bucket of paint, and aperture as a funnel. If the funnel has a smaller opening (say f22 or so) at the bottom the paint is going to have a controlled pour, and is not going to splatter. If you were to just flip the bucket over with no sort of funnel (say f2.8 ) the paint will splatter all over. This is where you get the shallow depth of field (OOF back ground.)..... Or something like that. It made sense to me.


  • thanks everyone


  • but technically speaking, light is reflected off of objects and the "light" that we are receiving is from objects. If we make a smaller aperture then its getting less light which means less light coming from objects, meaning less detail of objects? I dunno it just sounds weird to me. Im trying to think logically.

    If a smaller aperture is less light then it sounds like something should be cut off of less detail. But infact its the opposite for detail, everything is sharp and crisp.

    A couple answers here: http://photo.net/bboard/q-and-a-fetch-msg?msg_id=0006DG

    Basically what it said is that the light rays are more scattered with larger apertures, resulting the blurryness of areas you didn't focus on. A small aperture makes the light rays more "tidy" when they have to fit through a smaller hole, resulting in more DOF.

    Make sense?


  • ronenfox (http://thephotoforum.com/forum/member.php?u=29432) answered it better so I removed my post.


  • but technically speaking, light is reflected off of objects and the "light" that we are receiving is from objects. If we make a smaller aperture then its getting less light which means less light coming from objects, meaning less detail of objects? I dunno it just sounds weird to me. Im trying to think logically.

    If a smaller aperture is less light then it sounds like something should be cut off of less detail. But infact its the opposite for detail, everything is sharp and crisp.


  • thanks


  • Prodigy,

    All the answers above are correct but you also have a valid point in your question. Decreasing aperture does increase DOF but at a price. You are right (in a simplistic version) with your question about smaller opening decreasing quality.

    The reason for that is lens diffraction. Google that and you will get a few explanations. All lenses get to a point where the benfit of increased DOF takes away from the detail of the focus area or sharpness. Better quality lenses limit diffratction better then other lenses but it is still there.

    Go out and take a picture with a large aperture and then stop it down all the way i.e f22. Even though the f22 photo has overall way better DOF look at the point you actually focused on. You will notice that there is more detail at the focus point in the photograph with the wide open aperture. If you used a tripod to take the pictures hence eliminating camera shake as a reason then that loss of detail is because of defraction.

    That's why it is good practice to use an aperture that gives you your required DOF and not automatically stopping down to f22 just because you think that will give you better DOF. You will lose detail depending on your lens.

    Maybe someone here has the time to explain the principle of diffraction but if you google it you should find plenty of answers.


  • You cant think of it as limiting the picture. But instead limiting the light.


  • Here are some links to other threads here that mention diffraction:

    link 1 (http://thephotoforum.com/forum/showpost.php?p=1217531&postcount=6)

    link 2 (http://thephotoforum.com/forum/showthread.php?t=106106)

    link 3 (http://www.thephotoforum.com/forum/showthread.php?p=991024)

    Best,
    Helen







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