Tutorial Challenge - Basics of Exposure
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Thread: Tutorial Challenge - Basics of Exposure

  1. #1
    iteach73
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    Default Tutorial Challenge - Basics of Exposure

    There has been a common theme with many of the questions that have been posted - EXPOSURE. In other words, what do you need to know about exposure to use manual settings to create the "perfect"picture. I will be adding pictures tomorrow to demonstrate each area. I know visual learners need to see it in action to understand.

    There are three things you need to know in order to understand exposure....aperture, shutter speed, and ISO. I will explain each and then talk about how they work together. The information in italics are more detailed, technical explanations. Feel free to skip over if it is overwhelming.

    APERTURE
    Inside your camera is the aperture diaphragm. This diaphragm opens and closes like the iris of your eye to let in light. The more open your aperture, the more light that comes in. Apertures are denoted by f-stops. The f-stops are actually fractions (the fraction indicates that the lens opening is that fraction of the focal length of the lens. So if you have a lens that is 50mm, and you are using an f-stop of f/2, that would be a fraction of 1/2, which would be 1/2 of the focal length of 50mm, so the lens opening would be 25mm) .

    An aperture of f/2 would have a larger lens opening than an aperture of f/11. If you remember f-stops are actually fractions, it is easy to see that 1/2 is a larger fraction than 1/11.

    Everytime you change between one aperture to another you are going up or down stops. The whole stop apertures are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22...Each aperture lets in exactly half of the amount of light as the aperture before it. Most advanced cameras allow you to stop up or down in fractional increments, so you may see f-stops such as f/3.5

    Here is a picture I found that gives you an idea of what an aperture diaphragm looks like inside your camera. As you can see, the smaller the f-stop number, the more open your lens is, which lets in more light.

    http://photographertips.net/wp-conte...5/aperture.jpg

    SHUTTER SPEED
    The shutter speed is just what it says. It is the speed at which your shutter opens and closes in your camera. The amount of light that is let in is determined by the aperture. How long your cameras sensors are exposed to that light is determined by the shutter speed. The faster the shutter speed, the less light. The slower the shutter speed, the more light is let in.

    You will also see shutter speeds denoted in fractions. These are all fractions of a second. So a shutter speed of 1/30 is 1/30th of a second. As soon as you see the ", that indicates that you are dealing with full seconds. So a shutter speed of 1" would be 1 second.

    ISO

    The last thing to consider is the ISO. You will not adjust this very often. ISO comes from the speed of the film (remember the film days?) The lower the ISO number, the less sensitive it is to light. So on bright sunny days, when you dont need your "film" to be sensitive to light (you have plenty of it) you can choose a lower ISO. When you need all the light you can get in darker situations, you will need an ISO that is more sensitive to light.

    As nice as it would be to always use a high ISO and get all the light possible, the price is grain. The higher the ISO, the more grain you will see. So for sunny days, you will probably choose 100-200. For overcast, or well lit shots indoors, you will choose 200-400. For dimly lit shots you will use 400-800. With really poor lighting, you will probably need to use an ISO of 800-1600.

    Putting it all together

    Now how does it all work together? The key is the right balance...you want the right aperture to balance with the right shutter speed to balance with the right ISO. The question is, how do I know what the right aperture is? the right shutter speed? the right ISO?

    Remember that photography is all about light. Too much light, and you shot is overexposed. Too little light and it is underexposed. To make sure you have the right amount of light, you want to use that nifty in camera tool....the LIGHT METER!

    You will see your light meter in your viewfinder as shown something like this.

    + . . | . . | . . 0 . . | . . | . . -

    Your light meter might have numbers instead of lines, it might have the minus and plus signs on the opposite sides.

    When you are adjusting your exposure by fiddling with the aperture and shutter speed, you will see a bar go to the left or right of the 0. If it is going to the left (or towards the plus) that means you are letting too much light in and you will overexpose your shot. If it is going to the right of 0 (or towards the minus), you aren't letting enough light in and you need to add more or you will underexpose your shot. You want there to be no bars on either side, which would indicate the exposure value is at 0, which means you have a "technically" perfect exposure.

    Now, when determining what aperture to choose, what shutter speed to choose...ask yourself, "What am I photographing? What do I want to capture?"

    If you are taking photographs of little ones, or if you want one thing in your shot as your focus (a flower for example)...you will want an open aperture. This will give you the Depth Of Field you want (this is the blurriness in the background, also called bokeh.). This will also allow you to have a faster shutter speed to help freeze motion better, which is important with those quick kids we all have! So choose an open aperture, then adjust your shutter speed until your light meter indicates a perfectly exposed shot.

    If you are photographing a larger landscape, where you want more in focus, you will choose a more closed aperture, or a larger number. This lets less light in, so you need to slow down your shutter speed. You will probably need a tripod in these instances, since even the smallest amount of camera shake (even if you THINK you were still) can be noticeable. So choose a smaller aperture (larger number) and adjust your shutter speed to so your light meter indicates a correct exposure.

    If you are photographing action shots, you will want to choose your shutter speed first. You will need a pretty fast shutter speed to freeze motion. Obviously the faster moving objects (runner, speeding car, etc.) will require a pretty fast shutter speed (1/1000 +). When you use a faster shutter speed, you are getting less light in, so you will need to open your aperture. So choose a fast shutter speed, and adjust your aperture so your light meter shows a perfectly exposed shot. You will probably have to do more adjustments here if you notice your shutter speed wasn't fast enough for the action you are shooting.

    YOUR CHALLENGE

    There isn't a specific photograph I am looking for you to take. I want you to go out and play with your camera in full manual. Get acquainted with your light meter. Adjust your aperture, your shutter speed, etc. Shoot one object and start at an open aperture (somewhere around f/4.5). What shutter speed did you need? Now go up a stop in aperture, adjust shutter speed. Keep doing this for the full range of apertures. How did your photographs change?

    Come back here, post pictures, ask your exposure questions. This is what you really need to understand in order to understand how to take a good shot. It is a common misconception that your camera knows better than you....sure your camera might take some good photographs in auto...but trust me, you will take better photographs in manual. You just need to understand exposure.

  2. #2
    CarrieJo78
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    Ok, this is probably a really dumb question, but I haven't gotten this far in my manual or readings yet. What should my camera be set on to choose all these? I know when it is on Av I'm in control of aperature and on Tv its shutter speed. Otherwise, I've only used auto. I'm not completely sure what everything on the dial means yet.

    Sorry if this is a really dumb question. I really want to try the challenge this week and have a lot to learn, but it would probably be best to know where to start.

    BTW I have the Canon Rebel XT. Don't know if that makes a difference.

  3. #3
    iteach73
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    Quote Originally Posted by CarrieJo78
    What should my camera be set on to choose all these?
    Not a dumb question! You want it set to M for manual. This will allow you to adjust aperture and shutter speed. ISO is set somewhere else, I am guessing in one of your menus (I dont have Canon, so I can't say exactly where it is)

  4. #4
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    I have the Canon and ISO is set in Menu 1 underneath Metering Mode.
    HTH.
    Magz
    Married to Christopher (June 2003)
    Mummy to Miriana (June 2004), Georgina (February 2006) and Emilia (December 2007)


    http://www.fertilityfriend.com/home/913c8

  5. #5
    Mega Poster michelle_cjs's Avatar
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    iteach -

    First I have to comliment you on your teaching skills. Awesome instruction! I feel like so many things "clicked" with me this time. I'm so anxious to get some shots for the challenge.

    Secondly, I feel sooooo stupid!!!!! I have always thought my images were so dark and nothing I did with aperture and shutter speed seemed to help. I thought I just wasn't getting it! All the technical stuff with the fractions and remembering small number equals larger opening and more light, etc. just confused me when it was time to actually take the shot. I got so frustrated with it that I went from Manuel setting to AV so I could set the aperture and see what the camera set the shutter speed at. I felt like I was regressing but knew that if I wasn't getting it right that I should go back to basics.
    After your Basics of Exposure post with the light meter diagram, I realized that I always thought my + was on the left and my - on the right. WRONG! My camera has the signs on the opposite as your diagram. I feel like Carlos Mencia "Duh Duh, Duh!" I always shot just with the meter just to the left of my center, thinking it was making it a little lighter. I was actually having the opposite effect. Maybe that's why I turn all my images into black and white! :rofl:

    Anyway! I'm so freakin excited to get out there and try it out for the challenge!
    ~Michelle

  6. #6
    CarrieJo78
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    Thanks! I agree. These tutorials are great for learning.

  7. #7
    cinroa
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    another dumb ?Where on the XTi do I find the shutter speed I think I have everything else.

  8. #8
    hunnygirl
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    I *think* on the XTi, its the same dial as you use to change you AP, you just have to hold down another button near the shutter... (trying to remember from my Mum's XTi) there are others here who can tell you for sure though!

  9. #9
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    If it's the same as the XT, then you change the shutter speed by using the wheel behind the shutter button.

    To change the AP, you press the * button and turn the wheel at the same time.
    Magz
    Married to Christopher (June 2003)
    Mummy to Miriana (June 2004), Georgina (February 2006) and Emilia (December 2007)


    http://www.fertilityfriend.com/home/913c8

  10. #10
    Mega Poster michelle_cjs's Avatar
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    Here are two from today and the last one from last Thursday when I was practicing the same thing. The camera has been glued to my hand! I think these turned out pretty good. C&C always welcome!

    #1

    #2

    #3
    ~Michelle

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