Aperture

Discussion in 'Photography Beginners' Forum' started by lucki85, Mar 12, 2008.

  1. lucki85

    lucki85 TPF Noob!

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    So I think I understand Aperture after reading some books etc, but everytime I read the notes I took I seem to get confused, so I guess I am just looking for some clarification...

    Large # f/16= small opening (lets less light in though, right?) Full picture in focus

    Small# f/4 = Large opening (I'm also assuming lets more light in) Blurry background (If I was focusing on a person or something)

    If this IS the case I guess I am just a little confused...I would think the more light that is let in the whole picture would be in focus..I'm not really sure why I would think this, but it makes sense to me.

    I did look at some other aperture posts, but I guess I need clarification on how I am wording it :D
     
  2. Alex_B

    Alex_B No longer a newbie, moving up!

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    The 'amount of light' is irrelevant when it comes to depth of field. The amount of light determines only if an image over or underexposed. If you want it brighter at the same aperture, just let more light in by leaving the shutter open for a longer time.

    Depth of field is only determined by the aperture, as you said. If you take a very very tiny aperture, you do not even need any lenses to focus and depth of field will be more or less infinite. This is the whole idea of a pinhole camera. (OK, there is diffraction, which in the end limits pinhole photography, but this is another story.)
     
  3. Socrates

    Socrates TPF Noob!

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    You are correct regarding apertures. Regarding your confusion, you're over-analyzing. Think a bit. You can get just as much light through a small opening as through a large opening by adjusting the shutter speed appropriately. The bottom line is that volume of light has nothing to do with depth of field.
     
  4. Big Mike

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

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    You have it right.

    High F number is a small aperture opening.
    Low F number is a large aperture opening.

    A large aperture opening will give you a shallow DOF (depth of field), while a smaller aperture will give you a deeper DOF.

    The DOF doesn't have anything (directly) to do with how much light is being let it. It has to do with the physics of lenses and the angles at which the light travels through the lens.

    For more in-depth information...look up 'Circle of Confusion'.

    I don't think it's all that important to fully understand the physics of it...but it might help. It should be enough that you know the results...I think you are on the right track for that.
     
  5. lucki85

    lucki85 TPF Noob!

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    AH ok...thanks so much both of you.... This has been the one thing driving me crazy. Of course light has nothing to to with DOF...This has really had me stumped for a long time. Duh :p
     
  6. Sandspur

    Sandspur TPF Noob!

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    You already have three excellent answers from three people who KNOW what they're talking about.

    Accept this information ... and move on
     
  7. lucki85

    lucki85 TPF Noob!

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    SO I havent fully gotten into SS yet, but as far as I know A fast SS freezes the subject (1/500) and a slow SS shows movement or blurs the photo (1/30)
    What does this have to do with light?
     
  8. Socrates

    Socrates TPF Noob!

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    If a shutter is open for 1/30 second it will allow more light to hit the film/snesor than it would if open for only 1/500 second (assuming the identical aperture). Kinda like watering your lawn for an hour compared with watering it for fifteen minutes (assuming the identical hose).
     
  9. Alex_B

    Alex_B No longer a newbie, moving up!

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    well, if you stay naked in the extreme desert sun for two seconds (short exposure time / short shutter speed), not much will happen. if you do the same for 2 hours (long exposure / long shutter speed), you will get a nasty sunburn. So with longer shutter speeds apparently more light has reached your skin / sensor / film, whatever.
     
  10. Big Mike

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

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    It's got everything to do with light.

    You need a certain amount of light getting into the camera, in order to get an exposure (photo).

    The two main controls that we have to control how much light gets into the camera...are the size of the hole (aperture) and the amount of time (shutter speed).

    If you make the size of the hole, half as big (stop down one stop)...then you need to keep the shutter open twice as long, in order to keep the same exposure.

    I used this analogy the other day, I forget for who...
    Taking a photo is like filling a bucket with water. A full bucket is like a well exposed photo.
    You can open the tap a little bit (small hole) and fill the bucket in say 10 seconds. But if you open the tap twice as much...you fill the bucket in 5 seconds. If you open it twice as big again, you fill it in 2.5 seconds.

    It's the same with light getting into a camera. If you open up the aperture twice as big (one full stop), then your shutter speed will be only need to be half as long.

    So, we already know that a faster shutter speed will freeze motion. But when the light is not really bright...we might need to open the aperture more, in order to get enough light to be able to get an exposure at a faster shutter speed.
     
  11. lucki85

    lucki85 TPF Noob!

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    Oh ok, so I guess I hadn't gotten to that part yet....The shutter lets the light in (sorry if I'm sounding totally ignorant). Makes total sense now. Thanks!! Sometimes I just need a little clarification.

    (bare with me..to compare helps me understand better)
    So...In my notes I have "in bright situations small aperture is usually a NO" But this isn't correct because aperture really isn't about the light but the DOF....so maybe I should have "in bright situations a slow shutter speed is usually a no?" Unless having a small aperture will affect my SS??? Okay, I'm thinking that doesn't really make sense and now I am confusing myself again. I guess this is why I shouldn't read books and take my own notes assuming I know what the write is talking about :confused:
     
  12. lucki85

    lucki85 TPF Noob!

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    Okay, I think I need to go back and red BigMikes reply about 20 times because I think this answers my question....have any drawings? I am really a visual learner LOL
     

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