Correct Exposure...?

Discussion in 'Photography Beginners' Forum' started by Cheesecake, Apr 12, 2007.

  1. Cheesecake

    Cheesecake TPF Noob!

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    WHAT UP FOOS!!!

    Sorry I mean, Hi. I'm new.

    Anyway I am kinda confused on this Correct Exposure concept. I wanted some poppy colors and nice contrast so I started a tiny bit of research and I came across the "Sunny 16" rule. It goes like this:

    ISO 100
    F stop 16
    Shutter Speed 1/125

    And that is supposed to give you a good exposure in the sun. BUT, it seems like you can do that with any SLR camera with out actually looking at the knobs your turning.

    I guess what I'm trying to say is, whats the point of learning Correct Exposure if I can get it without knowing the exact number I'm using?
     
  2. Big Mike

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

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    All modern camera have built-in light meters...so you don't really need the sunny 16 rule at all.

    Camera meters are set to provide an exposure of 18% grey. If that is 'correct exposure'...then all is good. However, a lot of things will cause the meter to be fooled. For example, it would try to make snow 18% grey...but we know it's actually white. This is where you need to compensate from the meter settings, in order to get 'correct exposure'.

    Actually,'correct exposure' could mean anything...it's subjective. If you, the photographer, want so over or under expose the image...then you can do that.
     
  3. fightheheathens

    fightheheathens TPF Noob!

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    im not really sure what your asking

    are you asking why learn about correct exposure if your cameras auto mode can do it all the time

    or why learn about correct exposure if you can just use the sunny 16 rule.


    either way, you want to learn correct exposure.
    the camera auto mode has limitations, it doesnt know what your subject is or your desired effect. Knowing how to product a correct exposure gives you much more creative control then the cameras auto exposure mode.

    sunny 16 is just a guideline. It is a starting point and isnt always true. My understanding is the Sunny 16 rule is used for those times when you dont have a light meter handy. If you have an older camera, it might not have a light meter and you have to guess...Having a starting point makes your guesses more accurate. Another situtaion could be that you want to do some street photography but dont want to frighten people away every time you raise your camera to your eye. if you can guess at the exposure using something like the sunny 16 rule, then you can "shoot from the hip"

    i hope this helps, but maybe if you cleared up what exactly you want someone could give a better answer
     
  4. Cheesecake

    Cheesecake TPF Noob!

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    Wow you just blew my mind away... that was one of my biggest problems. And the solution was so simple.

    You just helped me out BIG TIME.

    THANKS!
     
  5. henryp

    henryp TPF Noob!

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    Would this were so. Camera meters are set to 12%. Grey cards are set to 18% because Ansel Adams (who invented the Zone System of exposure) managed to bully Kodak into using 18% because it corresponded to Zone V.

    Read more here.
     
  6. RedDevilUK

    RedDevilUK TPF Noob!

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    basically i take a photo, and look at it on LCD, if the colours correspond to what my eyes are seeing... and thats the look i want, then all is fine.

    if i look at the LCD and im not happy how it turned out, then i switch to manual and start tweeking :)
     
  7. MikeR

    MikeR TPF Noob!

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    There are multiple "correct" exposures for every shot. Your goal should be to get a "correct yet creative" exposure. You,not the camera, decides on the DOF you want, Do you want it shallow to isolate some flowers from the rest and the background? or do you want the entire field and background to be sharp? Just like if there is a breeze, Do you want to show the motion of the flowers moving,or do you want to freeze them?
    Then you need to put thought into your composition....
    The correct exposure is the one that gives you the results you wanted (Your vision of the scene),
     
  8. Garbz

    Garbz No longer a newbie, moving up!

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    Unfortunately this only works well if your LCD somehow represents reality. Unfortunately some cameras (My D200 I am pointing at you), the LCD is much brighter than a normal well tuned CRT. I only ever look at the composition on the LCD, to determine the exposure I typically use the histogram.

    Also before shooting blindly with the Sunny16 rule it's worth checking if it works well for your given circumstances. I typically call it more of a Sunny 11 :)
     
  9. bencze

    bencze TPF Noob!

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    I'm a newb in photography but I think the correct answer was already given: there is no such thing as 'correct exposure' :)

    I have a d50, and I always (99.9% of the time) use it on aperture priority, which means if there's anything NOT constant in my shots, it's the aperture size. :)
    I am getting a hang of DoF, but very slowly. I, however, would prolly use an f/11-16 for sunny days mostly, except if I want to isolate some object from the background...
    I don't think I could live without DoF (even if I still don't understand it fully and can't use it correctly, only guess). It amazes me and it intrigues me. Playing with it since months but it's still exciting for me to decide on what aperture sizes to use. I think it also depends on how far the subject is from me (if it is far away I use a small aperture size anyway).

    So, rules? Let's say:
    Sunny day: f/9 - f/16 maybe
    sunny day with subject close and background isolated: f/5.6 maybe (i guess shutter speed would be far less than 1/125 :D )

    Maybe it is easy for me to speak as I have metering on my camera. Can't imagine how it was in the old times. Different, could be a good word for it.
     
  10. EOS_JD

    EOS_JD TPF Noob!

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    Yes there is.... there has to be a correct exposure - but equally the answer is actually there are many correct exposures for the same scene.

    If the exposure is wrong it must be either over or under exposed - and this may not be a good thing. Best to always aim for a correct exposure.

    Lets say you meter a scene and it gives a correct exposure as

    ISO 100
    F stop 16
    Shutter Speed 1/125

    Now here's some other correct exposures for the same scene

    ISO100
    f11 @ 1/250th or
    f8 @ 1/500th or
    f5.6 @ 1/1000th or
    f4 @ 1/2000th or
    f2.8 @ 1/4000th

    all you have changed here is the depth of field but the exposure will remain the same (same amount of light reaching the sensor)

    Regards depth of field 4 things affect this.

    Sensor size (crop cameras have different dof values to FF)
    Focal length
    Distance to subject (distance to background will affect how this looks)
    Aperture size

    Look at a depth of field calculator and see the differences each change makes to the potential depth of field. http://www.dofmaster.com/dofjs.html

    The longer the F/L the shallower the depth of field
    The closer your are to a subject the shallower the depth of field will be
    The larger the aperture the shallower the depth of field.

    If you are 3m from a subject with a 200mm lens set at f2.8 and using a 1.6x crop camera the depth of field would be very narrow - 2cm!!!

    Standing at the same spot and using a 17-55 lens set at 17mm @ f2.8 the depth of field would now be 4.81m so focal length has transformed the image.

    Moving further away from the subject in example 1 would give this

    You're now 20m from a subject with a 200mm lens set at f2.8 and using a 1.6x crop camera the depth of field would now be 1.06m so distance to subject matters a lot too.

    Finally opening the aperture - lets look at examples 1 & 3 with the long lens

    If you are 3m from a subject with a 200mm lens set at f16 and using a 1.6x crop camera the depth of field would still be very narrow at just 13cm!!! Distance to subject and focal length used still maintains that narrow dof.

    You're now 20m from the subject with the 200mm lens set at f16 and using a 1.6x crop camera the depth of field would now be 6.16m.

    Last one is a 100mm Macro exposure. Say 10cm from the subject at a narrow aperture of f16 (on a 1.6x crop camera) - the depth of field is so narrow (0mm) that you probably need a very steady tripod to be accurate - and if the subject moves!!! Well good luck. It seems distance to subject and focal length make the biggest difference to depth of field.

    There's a huge number of different settings that give a correct exposure and it's down to the photographers creative ability to get the one that expresses what he wants to portray an image.

    Hope this makes sense

    Cheers
    Jim
     
  11. bencze

    bencze TPF Noob!

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    Makes a lot of sense. And I didn't express myself correctly, what I meant is that there is no fixed set of settings defined as 'correct' (as in, 1).

    I have seen some DoF tables. My problem is, I really can't be arsed to study them and memorize them. I think I will learn it with time and experience, but estimation - I have the luxury that I don't expect my photos to be perfect to the centimeter/millimeter since it's just a hobby. Also I think that more often than not, I cannot afford to take a DoF table out of my pocket and think about it for minutes... that's why I didn't bother. Maybe I will keep one with me after I get a nice camera bag to carry all my gear - could turn out useful in some situations.
    Your post made a lot of sens though, I just need to bookmark it and read it a couple of times. I think I did read/hear somewhere that focal length influences DoF as well, I just wasn't sure in what way. Your examples are very interesting, thanks.
     
  12. EOS_JD

    EOS_JD TPF Noob!

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    i don't carry one around either but by playing with it you will see the differences in focal length, distance and aperture make to a potential image. It's sometimes difficult to see it in an image in quite the same way.

    Thanks for the words.
     

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