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I am reading Bryan Peterson's book Understanding Exposure. Quoting text from the book:

I set up my camera and 75-300mm lens on a tripod. I set my focal length to 130mm and aperture to f/32 and focused a third of the way into the scene. With my camera pointed upward to the green leaves, I adjusted the shutter speed until a -2/3 exposure was indicated - 1/25 sec. I then recomposed to get the scene here and fired off several frames.

I have a couple of questions based on this.

  • What does he mean by -2/3 exposure and why is that required? There is a discussion about this in the book. But I can't understand it fully from the book.
  • Most of the shots which he explains in this book were taken by recomposing the scene. I am not understanding the concept behind recomposing. Why is that required? And how can I decide whether to recompose a scene or not?

I have a Canon 500D with the 18-55mm kit.

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3 Answers 3

up vote 14 down vote accepted

He initially pointed his camera so that the green leaves were in the center of the viewfinder. He didn't do this because he wanted them in the center of the photograph; he did this so that he could take a meter reading off the leaves, probably using spot metering, which is a metering mode that's sensitive to only a small area in the center of the view finder.

He the adjusted the exposure by -2/3 because he wanted those green leaves to be 2/3 of a stop darker than a middle tone.

He then "recomposed the scene" because he had only placed the leaves in the center of the field for metering purposes. That's not where they belonged in the photograph. "Recompose the scene" just means point the camera so that everything is where you want it to be in the frame.

(Just as the author recomposed after taking a meter reading, people will sometimes put an object in the center of the frame to focus on it, either using the central autofocus point, or a manual-focusing aid in the center of the viewfinder. Then they would recompose after focusing.)

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Thanks. But why is that metering leaves first and then recomposing required? –  Appu Apr 23 '11 at 14:54
4  
Because he wanted to spot meter off the leaves for the exposure setting and spot metering uses just the very center of the frame - but he didn't want to take a picture of the leaves in the very center of the frame. –  rfusca Apr 23 '11 at 15:39
    
Actually I think he mostly uses center-weighted metering in his examples. Also, spot metering meters the spot of your choice, not just the center - that's the whole point of it. @Appu: I believe this is in his 'Green Jeans' section. This, and his other sections like 'Brother Reflecting Sky', are ways of getting reliable metering results when faced with difficult lighting situations. So, in shady situations under leaves, you meter off of the leaves, and this generally gives you the correct exposure for the rest of the scene. –  ElendilTheTall Apr 23 '11 at 16:16
    
thanks a lot for the explanation. –  Appu Apr 23 '11 at 16:26
2  
Spot metering happening anywhere but at the center of the frame is a brand-new thing, and not even all current-generation cameras will spot-meter anywhere but the center of the frame. The author may have been using center-weighted metering, but the procedure for spot metering would be the same with most cameras. –  user2719 Apr 23 '11 at 20:41

A -2/3rds, as I recall, only is if you are primarily focusing on green things, specifically the dark green leaves that are common in some areas.

Recomposing the scene usually involves focusing on a point, and then changing where the camera is pointed to get the optimal picture.

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How will I set -2/3? Is this through the exposure compensation option available in the camera? –  Appu Apr 23 '11 at 14:55
    
@Appu What camera? –  PearsonArtPhoto Apr 23 '11 at 15:08
    
I am using Canon 500D –  Appu Apr 23 '11 at 15:13
    
@Appu: It absolutely can. It depends a bit on which mode you are in, but if you are in aV or tV mode, then you simply turn the dial down such that the arrow is -2/3rd from the 0. I think program mode can do the same thing, but none of the fully auto modes can. –  PearsonArtPhoto Apr 23 '11 at 15:17
    
thanks a lot. I will figure that out –  Appu Apr 23 '11 at 15:19

I found this video that shows the exposure compensation scale on the display of the camera. There's one just like it inside your viewfinder at the bottom. Check the bit of video at 1:30. You're looking for the scale that goes from -2..-1..0..1..2 just up from the centre of the screen. Then note the button near the top right corner of the display. It's labelled AV and has a +/- symbol. Press this and spin your dial to see it move. That's how to set your exposure compensation. enter link description here

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