Still confused on aperture...

Discussion in 'Beyond the Basics' started by Sarah23, Mar 10, 2008.

  1. Sarah23

    Sarah23 TPF Noob!

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    I feel DUMB asking all of this. But I think I've just made it harder on myself then it is, and I'm totally confused now.

    I thought I understood aperture. I know that the number represented on the camera/lens represents how big the aperture opens...and that the larger the number, the small it will open. I understand that obviously the larger it opens, the more light will get in...and vice versa.

    But beyond that, Im kinda lost. I guess I thought that that was IT...now I see people saying things like taking it down by a 2-3 stops to get it more clear/crisp...and something having to do with the speed of your lens depends on the aperture and a bunch of other stuff that I just didn't understand.

    Could someone either explain this all to me, or give me a site that explains it in a way I would understand...?

    Thanks so much :blulsh2:
     
  2. Mav

    Mav TPF Noob!

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    Not all lenses are at full sharpness at their "wide open" maximum apertures. For example, a cheaper f/2.8 lens might need to be stopped down to f/4 or f/5.6 to get optimum sharpness, whereas a more professional and much more expensive f/2.8 lens might be as sharp wide open at f/2.8 as the cheaper one is at f/4 or f/5.6. Most lenses need to be stopped down 1 or 2 stops to reach peak sharpness, but where they start at sharpness wise at maximum aperture can vary all over the map. Some will look superb even wide open, whereas others will be a bit soft and really do need to be stopped down to have a quality photo.
     
  3. jcolman

    jcolman TPF Noob!

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    Sarah,

    There is no such thing as a "dumb question". We all had to learn this stuff at one time or another.

    While there are plenty of web sites that explain photography much better than I can, perhaps the following will help. It's part of a "photography 101" guide I wrote for another web site.


    LEARNING YOUR WAY AROUND YOUR CAMERA

    The infinity symbol (sideways figure 8) is found on the lens and it refers to the maximum focus point (distance) of your lens. There are usually other numbers on the lens that are the focus distance in meters or feet. These numbers can be useful especially when figuring depth of field, which will be discussed later.

    The other markings on your lens (or that appear in your viewfinder) are the ones that confuse people the most. These are the aperture settings or F/stops. They often look like this:

    1.2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22.

    The F/stop markings on your lens may be slightly different but they all do the same thing and that is control how much light passes thru your lens to the film or pixals. Each setting is double the amount of light. For example, f/4 allows twice as much light as f/5.6 even though the numerical values don’t add up to double. Confusing? Yes. F/stops work in conjunction with shutter speeds to control how much of the ambient light hits the film or pixals to make a proper exposure.

    Note that f/stops may not be displayed on the lenses of modern Digital cameras, rather they are shown in the viewfinder or on the LCD screen. Also, the markings may be slightly different, by that I mean, instead of an f/stop of 5.6 as shown in the example above, your DSLR may display 5.2, 5.5, 5.8 or another similar number.

    F/stops also play a role in controlling depth of field. Depth of field refers to how much of your subject is in focus from near to far. The smaller the aperture (f/16 is smaller than f/8 for example) the more the DOF in your picture.

    Where you focus the camera also plays a role in DOF. The closer your subject is to the camera, the less DOF you’ll have. This is why macro shots have very shallow DOF.

    Lens selection is also crucial in determing how much depth of field you'll have in a given picture. The longer the lens (telephoto) the less DOF you’ll have. Conversely, the wider the lens, the more DOF in your picture.

    Your camera also has a shutter speed knob or dial. Most cameras double the shutter speed as you move up or down the scale. For instance, my camera's settings in seconds are:1 -/1/2-/1/4 -/1/8/-1/15/-1/30/-1/60/-1/125-1/250-1/500-1/1000. Most professional photographers can hand hold a camera at 1/30 sec with a wide angle lens and get a sharp picture but going any slower or using a longer lens requires a tripod or some other sort of camera support.

    Remember, most of the newer DLR cameras have the shutter speed/ aperture settings displayed on a menu or in the viewfinder and not on the lens or camera body. These "electronic" settings may vary from what I've listed but they do the same job, i.e. control how much light enters the lens to make the proper exposure.


    An "X" by the 60 or 125 shutter speed knob on older film cameras means that's the shutter speed at which your flash will sync with your camera. If you use a faster shutter speed the shutter itself will close before the flash has fully fired leaving part of your picture dark. You can always sync a flash at a slower speed. Some cameras like the Hassleblad use a different type shutter and will flash sync at any speed. Also, most of the newer DSLR cameras will flash sync at higher shutter speeds up to 1/250 sec.

    EXPOSURE

    Your camera has to have the right combination of light + exposure time to = proper exposure. Your shutter speed and your lens aperture work together to give you the correct exposure as determined by either you or your camera. (more on how to determine best exposure later). This means that if you change shutter speed you must also change f/stop (aperture) in order to keep the same exposure value.

    Lets assume that your camera's light meter tells you that 1/60 second exposure time @ f/11 will give you the correct exposure. If you were to place the shutter speeds and the f/stops (aperture) on a scale the following combinations would also give you exactly the same exposure value.

    1/15 - 1/30 - 1/60 - 1/125 - 1/250 - 1/500 - 1/1000
    f/22 - f/16 -- f/11 - - f/8 --- f/5.6 -- - f/4 - -- f/2.8

    Deciding which combination to use depends primarily on which is more important to the photographer, shutter speed or depth of field for this particular picture. Remember however, if you change shutter speed setting (or aperture) you must change the corresponding aperture (or shutter speed) setting to keep the same exposure value. Also, an important fact to remember is that most lenses are at their sharpest when "stopped down" 3 or 4 stops from their widest settings.

    For example. If your camera light meter tells you that 1/60 second at f/11 will give you the correct exposure and you want to increase your shutter speed to 1/250 sec you must open your lens aperture to f/5.6 in order to keep the same exposure value. You have to let in more light to compensate for the fact that you're now cutting the amount of time that the light will be exposed on the film or pixals.

    Remember, f/5.6 is two stops wider than f/11 and 1/250 sec is two shutter speed settings from 1/60. This is the easiest way to remember this as opposed to thinking; "hmm...1/250 is four times faster than 1/60 so I need four times as much light...." The math is much easier if you simply remember if you change your shutter speed by x number of clicks you must change the aperature the same number. And vice versa obviously.

    Faster shutter speeds means you need more light. Less light means you need slower shutter speeds.
     
  4. Tasmaster

    Tasmaster TPF Noob!

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    Woah, i was writing a few lines i thought might be helpful, then i hit the preview post button to be obliterated by jcolman's post! :hail: Well here they are anyway!

    Some quick and simplified info on aperture:

    Many lenses will produce a softer image at maximum aperture. You will get the sharpest image they can give when you stop them down a bit.

    A lens with a large maximum aperture allows more light to get in, so you can use faster shutter speed compared to a lens with a smaller maximum aperture at the same lighting conditions - hence "fast" and "slow" lenses.

    Depth of field is also depended on aperture. Large aperture will give you shallower depth of field, while a small enough aperture will keep everything in focus.
     
  5. jcolman

    jcolman TPF Noob!

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    :lmao: cut and paste ftw! I have a entire piece I wrote a long time ago devoted to teaching beginners. I just cut and paste then modify as needed.
     
  6. Sarah23

    Sarah23 TPF Noob!

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    Thank you!

    ok...so when someone says a lens is a faster lens...they are talking about the fact that because of the larger aperture, you can use a faster shutter speed...is that right?

    Im guessing I need to memorize that little graph thing that shows what shutter speed works with what aperture, correct?

    One of my biggest problems right now is that I dont know what combination of ISO, aperture, and shutter speed to use in what lighting.
     
  7. Big Mike

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

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    That's right.

    No, the combination will change when the light changes...which could be every shot. You just need to understand the relationship between them. So as long as the light stays the same, if you change one, you have to change something else to compensate (unless you want to change the exposure). For every 'stop' that you change the aperture...the shutter speed is either doubled or halved.

    You don't necessarily need to know that...because it could be different every time the light changes. Your camera has a built-in light meter that will essentially give you this information (just put the camera into any mode but M and half press the shutter release).

    As the photographer, you just decide what is most important to you. If it's DOF, then use an aperture that will give you the DOF that you want...then use the shutter speed and ISO that correspond to that...for the light that you have. If you want to freeze the movement of a subject or avoid blur from camera shake, then your shutter speed will be important. If low noise is your goal, then use a low ISO. If image quality is your top priority, then use a low ISO and stop down the lens from wide open (F8 is usually a good bet for quality).

    It's all about making compromises. Sometimes you can't use the aperture that you want, because you need a faster shutter speed. Sometimes you can't use a low ISO because you need a faster shutter speed etc. Sometimes you have to use a tripod because you want a deep DOF (small aperture) and the shutter speed would be too long to hand hold.
     
  8. jcolman

    jcolman TPF Noob!

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    Basically, yes. A "faster" lens lets in more light than a "slower" lens. In other words, a 50mm f/1.2 lens is "faster" than a 50mm f1.8 lens.

    Don't memorize the graph because it changes with every change in light. All you need to really know is that once you've determined a correct exposure (or more likely your camera has determined what it thinks is a correct exposure) any change you make to either shutter speed or aperture will affect the total exposure UNLESS you change both together. However, to confuse the issue even more, adding a strobe to the equation throws my previous statement out the window.

    edit: the previous poster said it better than me.
     
  9. TCimages

    TCimages TPF Noob!

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    here is a pic I posted in another thread. It may help.

    [​IMG]
     
  10. Sarah23

    Sarah23 TPF Noob!

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    Thanks Mike!

    I guess what I am still wondering then...is if you have to have your shutter speed at...lets say...1/30 because of a lower light situation...does that automatically mean that you need your aperture at f16? or is that going to vary along with everything else?

    I think I have a mental block somewhere...this seems like it should be a bit easier, and for some reason its confusing the crud out of me! Maybe im just not use to thinking about stuff like this...lol...my normal day includes watching Blues Clues with my 2 year old son and carrying around my infant while praying she doesn't spit up on me AGAIN...so im sure im just making this all harder then it is!

    I will learn...I just need to keep going over it and one day it will just click..I hope! I do have a friend who is a professional who is going to meet with me to help me out. :) Im very much a visual, hands type person when it comes with learning something new!
     
  11. Big Mike

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

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    No, you don't have to use or match the settings like that. If you were in a low light situation...you would use a larger aperture, because it would give you a faster shutter speed.

    Until you understand it better...just rely on your camera's meter (don't use M mode (for now)). I suggest using Av or Tv mode. This lets you choose one setting and have the camera give you the other.

    When you take a shot (or just when you hold the camera up to your eye) watch what settings you are getting (numbers in the viewfinder). Notice that when you change one of them...the other will change to correspond. Notice how they when you point the camera at something bright...and when you point it at something dark.

    Don't worry about not getting it. I've found that a lot of people have a hard time wrapping their heads around it...but then comes a 'Eureka' moment when it all starts to fall into place.
     
  12. Sarah23

    Sarah23 TPF Noob!

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    OK...well I won't be using stobes any time soon....I dont even know what it is, really. :lmao:

    The real problem I have is in situations where there is less light. I guess this is probably a problem for a lot of beginners from what I have read on other threads, too, though.

    Like at my in-laws...their house is very dim. Even during the day. Its been really hard for me to take pictures there....they all come out too dark, even with the aperture open to its max, and taking the ISO to 1600 (which I dont like doing at ALL) I cant seem to get the right exposure unless I lower the shutter speed to like 1/5 or 1' or something like that, which obviously doesnt help at ALL since im trying to take pictures of kids playing. I just end up with a big, dark blur.
     

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