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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 30 Jul 2013 (Tuesday) 23:56
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Fundamentals of Exposure

 
Wilt
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Jul 30, 2013 23:56 |  #1

This is meant to be a primer on exposure for those early in the stages of learning, to help to illustrate different situations that we might encounter in the real world, and how we might attempt to capture the 'impossible'.

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First, the illustration explained...
  • The Blue Box represents the Dynamic Range that can be captured by the digital sensor, and the thick blue line represents the Center of that Range.
  • The Black Scale represents the brightness levels present in the scene that we try to meter and set a suitable exposure. Again, the thick line in the center is what our meter tries to determine, the center brightness of an average scene, the legendary 18% middle grey tone centered in between White and Black.
Now the principles explained.
In the left column we illustrate the usual situation that we handle via ordinary metering and with ETTR (Expose to the Right) by the UNTHINKING man.

  1. Illustration 1 shows a ordinary scene whose Dynamic Range conveniently fits within the sensor's DR...very convenient and requiring no special thinking.
  2. Illustration 2 shows a wide DR scene whose DR cannot be captured by the sensor. In employing ETTR, we deliberated ignore the Shadows, and fit the Highlights within the range that we capture in the sensor, under the philosophy of 'Capture the Highlights, no matter what!'.
  3. Illustration 3 shows a wide DR scene whose DR cannot be captured by the sensor. In employing ETTR, we deliberated ignore the Shadows, and fit the Highlights within the range that we capture in the sensor. The problem with this approach is if we really care about shadow detail and there are highlights that we do NOT care about, with ETTR we nevertheless capture the highlights and lose the shadows -- the exact opposite of what we care about!


Now let's reevaluate the conventional (left column) approach and discover that there is an alternate way to think about each of the situations, as shown in the right column...the THINKING man's approach!


  1. Illustration 1a shows a ordinary scene whose Dynamic Range conveniently fits within the sensor's DR...very convenient and requiring no special thinking. No change to our conventional thinking needed.
  2. Illustration 1b shows a scene whose Dynamic Range conveniently fits within the sensor's DR, but the number of brightness samples in the Shadow area are fewer in count, so that the meter is wrongly biased in the direction of brighter scene sample count (as shown)...So we need to use EC +1 to correct the meter ('give more exposure') so that it instead suggests settings to correctly capture the full brightness range of the scene .
  3. Illustration 1c shows a scene whose Dynamic Range conveniently fits within the sensor's DR, but the number of brightness samples in the Highlight area are fewer in count, so that the meter is wrongly biased in the direction of darker scene sample count (as shown)...so we need to use EC -1 to correct the meter ('give less exposure') so that it instead suggests settings to correctly capture the full brightness range of the scene .
    .
  4. Illustration 2a shows a wide DR scene whose DR cannot be captured by the sensor. If we employ ETTR, we ignore the Shadows, and fit the Highlights within the range that we capture in the sensor, under the philosophy of 'Capture the Highlights, no matter what!'. Instead, we decide here that the 'Highlight areas really do not matter to me; I want to exposure for the Shadows!!!' -- and we choose to NOT blindly follow the principles of ETTR!
  5. Illustration 2b shows a wide DR scene whose DR cannot be captured by the sensor, and represents the bride in white against a snow scene. If we employ ETTR, we decide that we agree that we can afford to ignore the Shadows and fit the Highlights within the range that we capture in the sensor, under the philosophy of 'Capture the Highlights, no matter what!' and we choose to follow the principles of ETTR.
    .
  6. Illustration 3a shows a wide DR scene whose DR cannot be captured by the sensor, the black cat in a coal mine. In not employing ETTR, we deliberately choose to ignore the Shadows, and fit the Highlights within the range that we capture in the sensor. The problem with this approach is if we really care about shadow detail and there are highlights that we do NOT care about, with ETTR we nevertheless capture the highlights and lose the shadows -- the exact opposite of what we care about! Instead, 3a (like 2b) shows that we set exposure to capture the important shadows and ignore what we consider to be unimportant highlights within the scene.
  7. Illustration 3b shows a wide DR scene whose DR cannot be captured by the sensor. In employing ETTR, we deliberately choose to ignore the Shadows, and fit the Highlights within the range that we capture in the sensor. We have made a conscious decision to use ETTR because the Highlights truly are important to us!

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Exposure101
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Jul 31, 2013 02:04 |  #2

Could someone explain this in layman's terms please?




  
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PhotosGuy
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Jul 31, 2013 08:18 |  #3

Exposure101 wrote in post #16168821 (external link)
Could someone explain this in layman's terms please?

As Wilt said, it's a primer to give people an idea of what they're trying to accomplish. Lot's more has been said...

Metering is pretty much a black art at first, so see if these links give you some help while you're learning.
Need an exposure crutch?

Here's why I prefer the "Crutch" method in a lot of situations: Post #47


http://www.cambridgein​colour.com/tutorials/c​amera-metering.htm (external link)

Correct Exposure

Curious question while reading "Understanding Exposure"


FrankC - 20D, RAW, Manual everything...
Classic Carz, Racing, Air Show, Flowers.
Find the light... A few Car Lighting Tips, and MOVE YOUR FEET!
Have you thought about making your own book? // Need an exposure crutch?
New Image Size Limits: Image must not exceed 1600 pixels on any side.

  
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Wilt
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Aug 01, 2013 00:25 |  #4

Exposure101 wrote in post #16168821 (external link)
Could someone explain this in layman's terms please?

Sorry, I speak 'Photography', no habla simples Inglés :lol:


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Fundamentals of Exposure
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