Many volumes of information have been written about Understanding Exposure. Cameras do the best that they can but can only do so good before you, the user, have to "read" the scene...making adjustments.
It's like looking lighting when shooting with the pinhole cameras and deciding to shoot at a particular shutter speed depending on the amount of light outside, or if a cloud passes over during the middle of your exposure..
But it is more complicated than that because what is behind a subject can easily mess up your picture. In addition, who is to say what is right and wrong. Most would agree that the picture on the left is too dark. But, if he were looking away from the camera, rather than into the camera, or had his back to the camera, it would be fine to have him be so dark.
1/125 @ f/8 1/15 @ f/8
Further complicating the issue is that there are two types of Exposure Adjustments: Bracketing and Equivalent.
With Bracketing, you are making the picture darker or brighter, like in the picture above. Notice that the aperture stayed the same while the shutter speed changed. So, in the picture on the right, the slower shutter speed resulted in a brighter picture because more light was let in.
With Equivalent, you are using the same relative exposure such
that tones remain constant, but you are varying either the shutter speed of the
aperture for a desired effect. You may change the shutter speed for creative
control to show or stop motion. Or, you may change the Aperture for more or less
depth of field.
Of course, truly, the best solution for the above picture would be to use some matrix balanced fill flash, but that is a lesson for another page.
A general rule of thumb is if a person is looking at the camera. If a person is looking at the camera, it is important to get the skin tones correct. If a person is look away from the camera, it could be ok to present a silhouette treatment for the scene.
Think of exposure like this...everybody has a given exposure. I like to refer to DB...or Dumpster Baby from Sunny in Philadelphia.
With Equivalent Exposures, regardless of the exposure changes, each picture is going to be the same, only the background of the treatment of motion will be affected.
With bracketing, you will see changed in skin tones as well as tones through out the scene.
Equivalent Exposures Review - to help with Review Sheet Answers
EE= Changing the settings with OUT changing the exposure.
Aperture = Depth of Field
SSpeed = Motion
Depth of Field
Length of lens
Wide = Lots of D of F
Telephoto= Shallow D of F
Subject to Camera Distance
Closer = Shallower
Farther = Greater
Minimum Shutter speed: SS + length of the Lens
1/60 sec for a 50mm
1/30 for a 28mm
1/250 for a 200mm
Four exposure modes of basic camera (i.e. Pentax k100d and K50):
• P: Program…camera sets the correct exposure, setting both aperture and shutter speed. Modern cameras try for the best balance of shutter speed based on the lens, and an aperture that provides depth of field. ie. 1/250 @ f/8
• A: Aperture Priority…you set the aperture…the camera sets the shutter speed for the correct exposure.
• S: Shutter priority…you set the shutter speed, the camera sets the aperture fro the correct exposure.
• M: Manual…you set the exposure.
Creating your own Equivalent Exposure Calculator:
Using a Google Docs spreadsheet, in column B, starting at about cell 16, type in the exposure stops from fastest to slowest (fast in Cell B10...slowest in B24). Then, in column C, list out the Aperture Stops (fast to slow) opposite the Shutter speeds. Finally, in Column E, type out the Film Speeds (fast to slow). Here is a sample...with blanks...so you have to fill in the rest. :-)
Or, here is one created for you: https://docs.google.com/spreadsheets/d/1_YI0pFM7icrxVPKqJDhfdyXQ_WXCqDikIRd9LbDLbtw/edit#gid=0
Here are a couple of websites that will help you understand how lighting affects your exposure: