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GX1 - why do you need to use Exposure Compensation?

Discussion in 'Panasonic Cameras' started by rossi46, Mar 19, 2012.

  1. rossi46

    rossi46 Mu-43 Regular

    141
    Mar 1, 2012
    Hallo all,...

    My preference is mostly to shoot in Aperture Priority, and maybe at low lights to freeze scenes at dinner and so on, I would use Shutter Priority.

    As a newbie, I do not understand why there is a need for Exposure Compensation (but I do understand the need for Exposure bracketing)

    Aperture Priority -
    Now what I do is set an Aperture, then look at my LCD screen to see level of exposure.
    If it is too bright or dark, I change either the Exposure (shutter speed) or ISO level.

    1. Now my question is, what am I doing differently compared to using either +/ve or -/ve exposure compensation?
    What is the advantage of using Exposure Compensation in this scenario compared to how I adjust the exposure for each scene?

    Shutter Priority -
    When I set shutter speed priority, I look at LCD screen and adjust the aperture and ISO level to get the correct brightness or exposure I see on the screen.

    1. Now my question is, what am I doing differently compared to using either +/ve or -/ve exposure compensation?
    What is the advantage of using Exposure Compensation in this scenario compared to how I adjust the exposure for each scene?

    Tricky Light and colour conditions -
    As I understand from reading articles, Exposure compensation is used in tricky conditions such as snow, where the whites will trick camera to think that it is overexposed, thus the camera reduces the exposure....resulting in darker and grey coloured snow.

    I have never seen snow in my life....but assuming I am going to capture a scene with full of snow,....
    1. For example I use Aperture priority and look at LCD screen, then adjust the exposure manually by tweaking ISO and shutter speed......wouldn't I get the same result as using +/ve Exposure compensation?

    2. Or the exposure shown on LCD display is not accurate and will always show "real" colour of the snow, but when I snap, ....it shows under-exposed gray snow....meaning LCD display gives an inaccurate colour compared to actual shots?
     
  2. EthanFrank

    EthanFrank Mu-43 Regular

    87
    Oct 30, 2011
    When in Aperture Priority mode, adjusting the ISO and shutter speed won't change your exposure, as the opposite value will move to compensate for your change. Exposure compensation is the only way to change the exposure as the camera sees it in a semi-auto mode.

    What you described is manual metering...are you sure you're not in Manual mode?
     
  3. songs2001

    songs2001 Mu-43 Top Veteran

    693
    Jul 8, 2011
    You are not really using shutter priority or aperture priority, what you are describing is using manual mode.

    In aperture priority, you don't choose the shutter speed after you choose the aperture. Exposure compensation is there so you are telling the camera, pick a shutter speed that is one stop higher or one stop lower.

    Same with shutter priority, you aren't choosing the aperture, you let the camera choose.
     
  4. rossi46

    rossi46 Mu-43 Regular

    141
    Mar 1, 2012
    Hallo EthanFrank and songs2001,

    I was pretty sure I was using the Aperture Priority mode dial.
    Whenever I set the Aperture value, my GX1 will automatically adjust the exposure.

    But by pressing the dial, then I am given the options of changing the exposure value
    (in the bottom middle of screen with a "0" in middle, and vertical bars to the left and right).

    Is this to do with some settings on my camera allowing me the option to fine tune exposure in Aperture Priority mode?


    Coming to Exposure compensation, what does the camera do if you set for example -1/3 EV?
    Does the camera automatically slow down the shutter speed slightly compared to the full automatic preset mode in Aperture priority?

    Eg. I set F 2.5 aperture in Aperture Priority mode,
    if there is no Exposure compensation, the camera automatically calculates shutter speed of 1/25 seconds.
    If I set negative -1/3 EV, then the camera uses slightly slower shutter speed, for example 1/20 seconds.

    Is this how it works?
     
  5. EthanFrank

    EthanFrank Mu-43 Regular

    87
    Oct 30, 2011
    You've got it, but your calculations are backward. Less exposure will yield a faster shutter speed, not a slower one.
     
  6. MajorMagee

    MajorMagee Mu-43 All-Pro

    Feb 24, 2011
    Dayton, OH
    Think of it like a simple math equation.

    Exposure Value = Shutter Speed & Aperture & ISO

    The three characteristics on the right can be set to any of a wide assortment of values as long as they "add up" to the value on the left. That's determined by the meter reading of the scene.

    What you're doing by shifting the exposure compensation is adding or subtracting from the value on the left that the other three characteristics on the right are trying to be equal to.
     
  7. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    When you press in the dial and it "changes the exposure value", this is exposure compensation. That's what Exposure Compensation does, is to brighten or darken the image by adjusting the "secondary" setting (Aperture or Shutter) after you have defined the "priority" setting (Aperture or Shutter).

    In Manual mode, you adjust both Aperture size and Shutter speed to obtain the correct exposure (let's forget ISO for now, as that is a constant for all modes). The wider the aperture or the slower the shutter, the brighter the exposure. The smaller the aperture or faster the shutter, the darker the exposure. Most people will read off the camera's meter to see where the camera thinks is the proper exposure, and adjust those two settings as they please until it reaches 0 EV, or they may want it to stop somewhere else, like at +0.5 EV or -1.0 EV to show a higher or lower key image.

    In Aperture Priority, you set the aperture size then the camera will adjust the shutter speed for you until it reaches 0 EV. You can then use Exposure Compensation to adjust the shutter speed slower or faster for a brighter or darker image.

    In Shutter Priority, you set the shutter speed then the camera will adjust the aperture size for you until it reaches 0 EV. You can then use Exposure Compensation to adjust the aperture size wider or smaller to create a brighter or darker image.

    Remember that there is no technical "perfect exposure". Correct exposure is determined by how the photographer wishes the photo to look. 0 EV means that the exposure is neutral for the area it's metering off of (which could be a spot, a weighted area, or an average of the entire frame, depending on which metering pattern you choose, and where you lock the Auto Exposure). It's up to you to decide if the photo should be exposed more or less from that 0 EV reading. As many people are trying to capture "what they see", this may mean that you will have to dial in a negative EC value in a low-key (darker) scene, because the camera will want to "compensate" for the darkness by overexposing, thus losing the depth of shadows that you experienced. And of course, it often works the other way for higher-key scenes, where the camera will try to darken the exposure in order to "compensate" for the overall brightness it sees. So you could say that Exposure Compensation is more often used as Exposure "Anti-Compensation", to return the scene to normal. ;)
     
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  8. shnitz

    shnitz Mu-43 Top Veteran

    989
    Aug 25, 2011
    Austin, TX
    Let's step back for a minute. Exposure overall is affected by 3 things: shutter speed, aperture, and ISO. Shutter speed is how long your sensor is exposed to light. Aperture is the size of the lens opening. ISO is the sensitivity of the sensor.

    Now, you say you like to shoot in aperture priority mode. In this mode, you set the aperture with your dial, and the camera will use the light meter to automatically choose a shutter speed. Therefore, you do not choose the shutter speed in aperture priority mode. For example, let's go look at a scene. You choose an aperture of f/2.8, and you set the ISO to 200. The camera chooses a shutter speed of 1/500 second. Now, you decide that f/2.8 is too blurry of a background, so you change the aperture to f/4. Adjusting the aperture does not change the brightness of the final photo! When you change the aperture, the camera will automatically compensate by adjusting the shutter speed accordingly.

    Now, let's stay in aperture priority, and then look at the photo we just took at f/4. We took a photo of a white house surrounded by trees and dark grass, which made the house so bright that there isn't any detail in it. So, we adjust the exposure compensation to darken the photo, in readings called exposure values, or stops. An exposure compensation of -1 stop means that the camera will adjust the settings behind the scenes so that only half as much light hits the sensor. Since we are in aperture priority mode, meaning that we set the aperture (instead of the camera), and we set a specific ISO (instead of letting the camera choose with auto ISO), what is the only setting left that the camera can adjust to alter the exposure? Well, if you look above, you'll see that the only option left is shutter speed. So, when in aperture pr

    Aperture priority mode means that you want a specific aperture, and shutter speed doesn't really matter to you, so you let the camera choose it. Shutter priority means that you want a specific shutter speed to stop movement, and aperture changes don't really matter to you, so the camera can choose the aperture for you.

    I don't know how you claimed that you were adjusting the shutter speed in aperture priority mode without adjusting exposure compensation. If you want to see the need for exposure compensation, go outside tomorrow at noon (hopefully it isn't cloudy) and have a light-skinned friend of yours wear a black tshirt, or a dark-skinned friend of yours wear a light tshirt. You'll quickly see that you are going to be limited on whether you can expose correctly for the tshirt or your friend. Or even right now, put a post-it note on a wall or ceiling fan, next to a lamp with a thin shade. You will see that either the light bulb is pure white, or the sticky note is too dark. Adjust your exposure compensation to get the other part of your subject in focus.
     
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  9. rossi46

    rossi46 Mu-43 Regular

    141
    Mar 1, 2012
    Thanks to everyone for the explanations.

    I understand Exposure compensation completely now:2thumbs:


    Ned's quote -
    "When you press in the dial and it "changes the exposure value", this is exposure compensation. That's what Exposure Compensation does, is to brighten or darken the image by adjusting the "secondary" setting (Aperture or Shutter) after you have defined the "priority" setting (Aperture or Shutter)."

    I did not know what I was doing is already called "Exposure Compensation"...:rofl:
    I thought Exposure Compensation is an altogether different mechanism to shutter speed and aperture value....

    The above explanation is for you too Shnitz,...in your last paragraph, you were wondering what on earth I am talking about...hehe:redface:
     
  10. rossi46

    rossi46 Mu-43 Regular

    141
    Mar 1, 2012
    I have got one more further question, though not totally related to the thread title, as I try my best not to create too many new threads....

    Ok guys,.....this time question is about the accuracy of GX1 LCD screen preview -
    - Assuming you have limited space on memory card to perform Exposure bracketing or White Balance bracketing -

    1. how do you approach or what method you use when performing exposure compensation?
    Looking at the LCD screen preview to see the brightness,...Is it accurate enough to look at LCD screen preview?

    How about the colour accuracy of the LCD screen?
     
  11. songs2001

    songs2001 Mu-43 Top Veteran

    693
    Jul 8, 2011
    1. If you use your camera enough, you'll know when to use exposure compensation without looking at the screen.

    But if you really want to be accurate, you can use the histogram.
     
  12. jim_khoo

    jim_khoo Mu-43 All-Pro

    Apr 9, 2010
    Kuala Lumpur
    i find the GX1 is usually under exposed...
    how much do you guys compensate exposure shooting the GX1 on Aperture priority mode?
     
  13. Jman

    Jman Mu-43 Veteran

    475
    Apr 20, 2011
    Columbus, OH
    It depends completely on the subject. You have to realize what your meter is doing. It's metering the scene to 18% gray. That is, if your scene is composed of middle gray (or middle color) tones, 0 EC will meter perfectly. If your scene is composed primarily of lighter tones, your camera will still try and expose them as gray (it has no idea whether the tones are lighter or there's more light in the room/outside, etc). So you have to tell the camera it's shooting a brighter scene, that is, dial in +EC. If you're shootingi something that's mostly black (or has huge chunks of black), your camera will boost exposure to render that as gray. So you need to tell it that the scene is dark...dial in -EC.

    For portraits, with caucasian skin, you're looking at about +2/3EC. Darker skin will require less EC, really pale skin might need +1 or so. Shooting in the snow, you'll be at +1 2/3 or +2. Shooting something all black, you'll be at -1 2/3, etc. You'll start to get a feel for it after a while.
     
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  14. Lawrence A.

    Lawrence A. Mu-43 All-Pro

    Mar 14, 2012
    New Mexico
    Larry
    Light meters have assumed since the cavemen that what they are measuring is an grey card of 18% reflectance. If the scene you're metering, or the spot you're metering, falls significantly outside that assumption, you're in trouble. At a white sandy beach, you'll get serious underexposure, and if you are photographing dark, sooty walls, they will be overexposed. Exposure compensation is a simple way to live with auto exposure systems and still deal with those situations. Your meter is going to try to render everything as reflecting 18% (more or less; manufacturers muck around with the number, and always have). Knowing that makes life a whole lot easier.
     
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  15. jim_khoo

    jim_khoo Mu-43 All-Pro

    Apr 9, 2010
    Kuala Lumpur
    is it correct to say that when shooting under heavy shades -EC is better than +EC?
     
  16. shnitz

    shnitz Mu-43 Top Veteran

    989
    Aug 25, 2011
    Austin, TX
    No, that is not correct. It depends on your subject. Let's say I take a photo of my girlfriend. Whether she is indoors at night, in the shade, or in the sun, the camera is going to try to make her a certain brightness. You need to look at each situation individually, and consider what metering system you are using.

    Spot metering will only look at a single spot in the image, and make that one spot the correct brightness. If the rest of the scene is evenly lit, then everything will look OK. If the spot that you metered off of is a lot darker or brighter than the rest of the scene, then everything else will accordingly be underexposed or overexposed. Matrix metering, which is what your camera is usually set to, looks at the overall whole scene, takes many many measurements, and decides on an average brightness level.

    Really, you should consider reading up about the general fundamentals of photography, as a lot of this information is explained better and in a lot more detail than I'm providing here.

    For example, let's put my girlfriend under a tree during midday. Now, I can decide how to shoot her. From one direction, there is nothing behind her except for shade, about the same brightness as she is. Taking a photo of her, I don't have to worry about exposure compensation. Now, I want to shoot a photo of her from the other direction, where you can see out onto the sunny field behind her. This is where it gets tricky. If I choose spot metering, then it will be fine, as the camera will only look at her brightness, and I won't need exposure compensation. However, if I use matrix metering, then the camera will look at the bright field around her, and it will darken the photo to compensate for it. In this instance, I would have to use exposure compensation to make sure that my girlfriend's face is properly exposed. And in that situation, I would actually want to use about +1 exposure compensation, instead of negative like you ask about.
     
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  17. Johnytuono

    Johnytuono Mu-43 Regular

    137
    Feb 10, 2012
    Lancs., UK
    HI
    I'd say mine underexposes at least 1/3 stop
    JohnyT
     
  18. moccaman

    moccaman Mu-43 Veteran

    281
    Jan 4, 2012
    Australia
    Great stuff in this thread, thanks to everyone who posted up their thoughts!
     
  19. vtsteevo

    vtsteevo Mu-43 Regular

    96
    Nov 20, 2012
    Well, the seach button works! This thread definetely helped me, but I have a couple of questions:

    1. In dim light, the actual image is ALWAYS darker then what was displayed on the LCD. During the day I don't have this problem. Is this normal?

    2. I still can't figure out how to properly shoot a subject set against a bright background. I tried spot metering the subject, but then the rest of the image is too bright. I am going to try exposure compensation tomorrow to see if that helps, but I have a feeling that won't do much since it will impact the entire images and not just the subject.

    Thanks,
    Steve