Aperture Help

Discussion in 'Photography Beginners' Forum' started by icu222much, Feb 8, 2008.

  1. icu222much

    icu222much TPF Noob!

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    I'm confused about aperture. I know that the aperture is an opening in your camera that opens and closes a certain distance, allowing for a certain amount of light into your lenses. I do not understand how this would effect the depth of field.

    I also tried to do an experiment to try to figure this out myself. On a table I placed my cell phone. I placed my camera on the other end of the table (about 3 feet away). The backdrop is a window overlooking the street. I took two pictures in aperture priority mode. One was at f/5, and the other at f/22. I didn't see a difference in the picture other then the fact that one was slightly brighter then the other. Am I missing something?

    Thanks,
    -Jon
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Welcome to the forum.

    There is a rather technical explanation that will explain the physics of this. Maybe look up Aperture, Depth of field and Circle of Confusion.

    In your example, the shot at F5 should have a background that is blurrier than the one at F22.

    However, one of the factors is the size of the medium (digital sensor). I'm guessing that you have a 'digi-cam' with a small sensor...which make it hard to get a shallow DOF.

    Also, F5 really isn't a large aperture. On your camera, F5 may still give you a very large DOF.

    A DSLR camera with a lens that has an aperture of F2.8 (or better yet, F1.8 or F1.4) you could get a much, much more shallow DOF.
     
  3. R0TT3NBURIT0

    R0TT3NBURIT0 TPF Noob!

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    For different lighting your suposed to change your ISO (more light is lower ISO) if your pictures are not the way you would like them play with ISO.
     
  4. Sontizzle

    Sontizzle TPF Noob!

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    Think of Aperture as the hole in your camera that lets in light. A bigger aperture means a bigger "hole" and thus, lets in more light. Conversely, a smaller aperture will let in less light. Aperture is probably the most confusing of the 3 settings because the number (f/stop) used to describe it may seem "backwards" to most people. The lower the number, the larger the aperture, and vise versa.

    For example, an aperture of f/2.8 is twice as large as an aperture of f/4.0 and will let in twice as much light. I've illustrated this below to help you visualize what I've just described:

    [​IMG]

    Aperture is usually controlled in 1/3 stops, so 3 clicks of the wheel is 1 full f/stop. For example, f/2.8 to f/4.0 is one full stop. f/3.3 and f/3.5 would be one third stops in between f/2.8 and f/4.0. The minimum and maximum aperture settings are dependent on the lens you're using. More expensive lenses will usually have bigger apertures. For example, a lens with a maximum aperture of f/2.8 will usually cost hundreds of dollars more than the same lens with a maximum aperture of f/4.0.

    Aperture doesn't just control the light entering the camera, it also controls what is known as Depth of Field (DoF). This is the primary reason for adjusting the aperture value on the camera and is extremely important to understand. Depth of field is simply a way of describing how much of your picture is in focus. A narrow depth of field will have very little in focus (blurry background) while a wide depth of field will have almost the entire frame in focus (detailed background).

    In the example below, the picture on the left has a wide depth of field where as the picture on the right has a narrow depth of field:

    [​IMG]

    Depth of field is controlled by the aperture setting. A larger aperture (smaller number) will have a very narrow depth of field. A smaller aperture (larger number) will have a wide depth of field. For example, in the images above, the left picture was taken at f/10 where as the picture on the right was taken at f/2. A good way to remember this relationship is to think of the aperture f/stops (numbers) as a measurement of depth of field. The smaller the number, the smaller the depth of field, and vise versa.

    So then, why would we ever want to use a large aperture (small number)? Wouldn't we always want the most detail possible? The short answer is no, because your aperture setting will vary greatly depending on your situation. If you're looking to isolate your subject or remove a distracting background, a narrow depth of field is the best way to do so. Your subject will be in focus and the background will be blurry. Depending on how far away the background is and how large your aperture is, the background can become so blurry that it almost looks milky. This magnitude of background blur is usually referred to as "bokeh" and is a desired effect for some pictures, especially portraits.

    [​IMG]

    An example of the exact opposite situation where you'd want maximum detail and a wide depth of field would be shooting a landscape or something very large. In that case, the background actually is your subject, so a blurry background would not be desirable.

    To recap:

    A large aperture is a small f/stop number (f/1.4, f/2, f/2.8 ).
    A small aperture is a large f/stop number (f/12, f/18, f/32).

    A large aperture will let in more light, but will have a smaller (narrow) depth of field.
    A small aperture will let in less light, but will have a larger (wide) depth of field.





    hopes this helps. i didnt write this but i found it helpful for me.
     
  5. evo5gsr

    evo5gsr TPF Noob!

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    Err...
     
  6. akazoly

    akazoly TPF Noob!

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    Sontizzle thanks :wink: Please explain me this (in more details):

    This magnitude of background blur is usually referred to as "bokeh" and is a desired effect for some pictures, especially portraits.
     
  7. Helen B

    Helen B TPF Noob!

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    For anyone interested, here is a link to what might be the full original article by Ben Fried. It's quite well written.

    Best,
    Helen
     
  8. adolan20

    adolan20 TPF Noob!

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    Aperture is hard to understand because we think a bigger number must mean a bigger opening. Get rid of that logic and substitute this one: F stands for focal length, the / is divided by, so now it makes sense. For example, when you divide by a bigger number you get a smaller result ( smaller opening) and when you divide by a smaller number you get a bigger result (larger opening). That's how I remember it at least, hope that helped.
     
  9. akazoly

    akazoly TPF Noob!

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    I use the Nikon 50mm f/1.8D lens. The maximum aperture is 1.8 and minimum aperture is 22.

    1.8 2 2.2 2.5 2.8 3.2 3.5 4 4.5 5 5.6 6.3 7.1 8 9 10 11 12 13 14
    15 16 17 18 19 20 21 22

    What this mean, f/1.8 to f/2.5 is one F-stop for me ?
    Thanks!
     
  10. Sontizzle

    Sontizzle TPF Noob!

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    in english it means the bigger aperture (smaller number) will give u a more blurred background and a smaller aperture (bigger number) will give u a less blurred background ( a more clear picture).
     
  11. Sontizzle

    Sontizzle TPF Noob!

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    hmm i think 1.8 to 2.8 would be one full f stop (1/3)
     
  12. Helen B

    Helen B TPF Noob!

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    Yes, f/1.8 to f/2.5 is one stop.

    You multiply or divide the f-number by 1.4 (or 1.414, the square root of 2) for each stop. Starting at the minimum possible f-number, f/0.5, the sequence of full stops is as follows:

    0.5
    0.7
    1
    1.4
    2
    2.8
    4
    5.6
    8
    11
    16
    22
    32
    45
    64
    90
    etc.

    Best,
    Helen
     

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