Aperture and ISO (I'm confused how it related to photos)

Discussion in 'Photography & Video' started by Revenger, Jul 9, 2009.

  1. Revenger

    Revenger Member

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    Just got myself a 500D and trying to learn the basic settings so I can take good photos.

    I'm confused about Aperture and ISO though.

    I know aperture is the whole in the lens so to say to let light through and ISO is the sensitivity of the sensor to the light.

    But after reading a few sites I'm still confused how they relate to actual photos and the actual difference in the quality when from what I can see they both limit the light coming in in a way.

    Even the basic websites seem to be too complex to read on this.

    So can someone explain it like there explaining it to a 7 yr old ditsy blond girl thanks.

    Shutter I'm fine with mostly as that's the amount of time to let light in which is pretty easy to understand especially for photos of Ferris wheels, car trails etc.
     
  2. methd

    methd Member

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    Aperture - the size of the hole inside the lens that lets light in. Small F numbers means it's a BIG aperture (eg f1.4, f2). Large F numbers means it's a small aperture (f18, f16).

    Obviously, smaller apertures will let less light in and so you need to find another way to let more light in if there's not enough light. You can then raise the ISO or shoot for a longer shutter speed.

    Drawbacks of large apertures - by letting more light in with a larger aperture, you lose the large depth of field. DOF is desirable for landscape photos and those where you want everything or more than one thing in focus. Sometimes, as in portrait photography, this is a good thing, and we try to narrow this DOF to throw as much of the background out of focus as possible.

    ISO - Is the sensitivity of the sensor to light. It's used as a last alternative when you don't have enough light and you've maxed out both your aperture (largest setting) and your shutter (slowest shutter speed before things start to blur).

    Drawback of raising the ISO is you get noise. Sometimes, such as B&W arty shots, noise is desirable, but more often than not, it's not and should be avoided unless you have no other choices.
     
  3. pec_tacular

    pec_tacular New Member

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    Set up a shot with something in the foreground and take the same shot twice using your AV setting, one with aperture as large (smallest number) as you can and one with aperture as small (largest number) as you can, compare. Notice how the depth of field changes with the parts of the photo in focus as well as the required shutter speeds to expose correctly.

    Do the same for ISO. When you have a look on the comp, have a close look at 100% crop. Probably the easiest way to see for yourself.
     
  4. OP
    OP
    Revenger

    Revenger Member

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    Did the tests with a Anime figurine I have can really tell the difference between them.

    I spose toy can assign the focal length somewhere as the tip the base was in focus and on the low aperture and the figurine was slightly blurry
     
  5. MeeCrob

    MeeCrob Member

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    whats explained about is pretty much what the F stop (aperture) and ISO relate to. In the end, the lowest common denominator is the shutter speed. They are used to obtain the shutter speed you need to use to get the picture you want.

    Depth of Field (DOF) and noise are by-products of aperture and ISO respectively which with more skill, can be used and tweaked to compose the picture as you need to be.

    My suggestion is be aware of DOF and noise, but start more simply and worry about shutter speed. Theres no point if the end result is a blurry photo
     
  6. StormWaterdrain

    StormWaterdrain Member

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    As you have bought quite a capable camera, but lack the basic understanding to use the advanced features, I can suggest a couple of things....

    1) Keep searching the internet. There are thousands of basic explanations out there, some with animated pictures to help you understand. Here's some:

    http://digital-photography-school.com/aperture-101
    http://eirikso.com/2008/12/02/aperture-shutter-speed-and-iso-explained-visually/

    2) Use the camera in full auto mode, then review the information about each shot for ISO, Aperture and Shutter Speed information. Try and apply what you learned in (1) above to further understand.

    3) Consider purchasing one of the excellent guide books available for your camera, which will also teach you much of the basic photography fundamentals. This book specifically will be a great help to you:

    http://www.amazon.com/gp/product/1435454960/ref=pe_5050_12250210_snp_dp

    4) Think about a course that you can do. I am on one at the moment, which is full of people in your shoes and week to week they are making amazing gains in ability and understanding.

    All of the above is just the mechanics. You can master all of the above and still take crap photos, as (in my opinion anyway) the art of composition cannot be easily taught.
     
  7. FB008

    FB008 Member

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    Hello and welcome to the wonderful world of Aperture
     
  8. RyoSaeba

    RyoSaeba Member

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    Ok i'll try explaining with some examples for aperture.

    These 2 shots are taken at similar distance. They were not taken as an examples of aperture, but does give the idea on how it works. All shots are done at ISO 100.

    Shot 1.
    [​IMG]
    Shot at f/11 with a 6 sec exposure time.

    Shot 2.
    [​IMG]
    Shot at f/2.8 with a 0.6 sec exposure time.

    As you can see with the 2 comparative shots above. The first shot, the character is pretty much in focus all over. The Depth of Field (DOF) is pretty large.

    The second shot only the head is clear. The rest of the body is blurry and the further you get away from the face the blurrier it gets. That's a very narrow DoF.

    That's what you get with a small aperture. The f/number is the aperture setting. The smaller the number the larger the aperture. (i know it's reverse) The larger the number the smaller the aperture. ie f/22 is the smallest aperture. It lets the least amount of light through. So the smaller the aperture the longer you need to open it for the light to come through. But it gives a larger DoF.

    It's a little getting used to. Once you do it a fair number of time, you'll get the idea and the hang of it.

    Basically if you want things behind and infront of the main point of focus to be blurry then you would have a large aperture (smaller f-stop number). If you want as much of it to be clear then you'd use a smaller aperture.

    I hope that helps. :D
     
  9. OP
    OP
    Revenger

    Revenger Member

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    A great post explaining.

    Its what I achieved earlier with my figure on the kitchen top but nice to see it done again by someone that knows more then me about taking photos.

    @ StormWaterdrain thanks for the info will go allot of Googling and review the auto mode.

    @ FB008 thank you

    Also Ill look at the gallery and see what people use on shots I like.

    I'd post my own attempts if I do something good but I have no clue on PP also and want to concentrate on just taking photos atm.
     
  10. ^catalyst

    ^catalyst Member

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    Just remember the ISO, Aperture and Exposure time (shutter speed) all make up the final exposure.

    So;

    1/60th - F/2.8 - ISO400
    would be the same as
    1/30th - F/2.8 - ISO200

    See what we've done there is take 1 stop from the ISO (going from 400 down to 200) and put it on the exposure time (from 1/60th to 1/30th)

    A 'stop' is a half or double of light, So going from
    ISO 200 to ISO 400 = 1 stop
    1/60th to 1/30th = 1 stop
    F/2.8 to F/4.0 = 1 stop

    Lens stops go :

    F/1.4, F/2.0 F/2.8 F/4.0 F/5.6 F/8 F/11 F/16 F/22 F/32 F/45

    You can also shoot in half or even thirds of a stop, which will give you Apertures like F/1.8 or F/2.4 or even F/6.3!!!
    ISO can also usually be done in halves or thirds, you'll get ISO64, ISO160, ISO640 etc etc.

    Aperture controls the Depth of Field
    Shutter speed controls the time
    ISO sets the sensitivity

    So for sports where you want frozen action a high shutter speed would be favorable, in this situation a large maximum aperture say F/2.8 would be preferable as this lets more light into the camera; in turn reducing the exposure time (shutter speed).

    1/500th , F2.8, ISO400 = Frozen subject (1/500th) Shallow depth of field (F/2.8) and moderate/low grain/noise (ISO 400)

    Let's do the same thing with a different shutter speed

    1/125th, F/5.6, ISO400 = Slight subject movement (1/125th) Moderate depth of field (F/5.6) and again moderate to low grain/noise (ISO400)

    See how the overall exposure (you can call it brightness, but don't...) is the same, but the resulting image is different due to the variables being altered.

    -Lachie
     
  11. alexc

    alexc Member

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    They actually explain all this in the little book that comes with your camera. It's well worth reading :D

    RTFM as they say :D :lol:
     
  12. Deftone2k

    Deftone2k In the Darkroom

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    Yes but tbh i find with technical documents like that, it can sometimes just seem like you are reading the same thing over and over. You grasp the concept but sometimes you can struggle on certain aspects, or how they all mingle together.

    Pretty good explanation given here :thumbup:
     
  13. OP
    OP
    Revenger

    Revenger Member

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    Yea am going through the book but they don't explain it easily enough and really how it all meshes together.

    Another question now I'm playing around.

    I was taking pics of flowers and the more I zoomed in the more the focus was on the flower and less on the background even though the aperture was higher being 5.6 instead of 3.5.

    Can someone explain how this related?
     
    Last edited: Jul 9, 2009
  14. alexc

    alexc Member

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    mmm, maybe. I'd thought it was a decent simple intro, but then I had learned a bit by the time I read the story that came with my 40D :/ So YMMV :D
     
  15. MCWB

    MCWB Member

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    Last edited: Jul 9, 2009
  16. ^catalyst

    ^catalyst Member

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    Depth of Field (don't confuse with focus) becomes 'less' with longer focal lengths and higher magnification.
    This is why most macro shots are taken at small apertures say F/8-22.
     
  17. cvidler

    cvidler Member

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    Sounds like the OP is running into the limitations of the kit lens.

    It can do a biggest aperture of f/3.5 at the widest zoom, but zoom in, and it can only do f/5.6. It's a limitation of the lens.
     
  18. OP
    OP
    Revenger

    Revenger Member

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    Yea I know what the limitations are I was just curious why I kinda for a reverse DoF effect than what was explained above about aperture.

    Just trying to piece how all the terms goes together to make up the different effects currently.
     
  19. kenpachi

    kenpachi Member

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    not to hijack the thread but im also a noob and still trying to get the hang of aperature and iso.

    question. based on what has been said so far, the smaller the aperature, the smaller the DOF.

    so how is it that the following possible.

    http://www.flickr.com/photos/tristenmurray/3482976316/

    the person is using a f1.8 and he managed to get a very small DOF.
     
  20. ^catalyst

    ^catalyst Member

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    Don't multiply f stop by focal length.. DIVIDE it.

    Aperture is expressed as a factor of focal length (focal length:maximum aperture - e.g 50 / 1:1.8)

    50 / 1.8 = 27.7mm
    50 / 2.8 = 17.85mm
    50 / 8 = 6.25mm

    So, smaller apertures are expressed as larger numbers, therefore f/1.8 is quite a large aperture, whereas f/8 is significantly smaller.

    With anything in photographics, when in doubt, think inverted.
     
    Last edited: Jul 10, 2009

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