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Author Topic: Metering with XT  (Read 4437 times)
Littlefield
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« on: July 07, 2007, 02:31:39 PM »
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I saw this about metering . With the XT it would be with partial or Center , eval

"Why do we need to get technical about light metering when we have a simple tool called a light meter to do all the work for us. The simplest way to visualize a light meter is to use the spot meter, set the ISO, put your camera on M and set an aperture. Point the spot meter at a neutral toned subject and set the shutter so the indicater marks the centre of the scale. Now point at the lightest part of the image and note if the reading is more the +2. Next look at the darkest part and note if the reading is less than -2. It the brightest part was much over +2 your exposure will blow out the highlights. If you don't want this to happen you will have to close down or slow down a bit (or both) so that the brightest part of the scene will read not much more than +2. The rest of the image may be dark, but you have saved the highlights. A similar process on not having the darkest part of the image less than -3 can be used to avoid blocking up the shadows. If you can't find an exposure setting that is within this range for both the darkest and brightest parts of the image you will have to compromise and accept some blown highlights or blocked shadows.''

When he says point the camera at the lightest area to see if it is more the +2 he does not mean setting the camera back to 0 right ? I mean you take a reading off sky by centering camera to 0 and then just move the camera to the shadows or lighter area to see how much difference there is without moving the neddle back to 0 ,the middle right ?

Thanks I am trying to relearn this digital stuff after using  a X 700 back in the late 1980's.
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Jonathan Wienke
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« Reply #1 on: July 07, 2007, 03:16:57 PM »
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Read http://www.visual-vacations.com/Photograph..._strategies.htm
it has everything you need to know.
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Littlefield
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« Reply #2 on: July 07, 2007, 04:25:02 PM »
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Read http://www.visual-vacations.com/Photograph..._strategies.htm
it has everything you need to know.
[a href=\"index.php?act=findpost&pid=127023\"][{POST_SNAPBACK}][/a]
Thanks ,good stuff but it did not answer my question.
Don
« Last Edit: July 07, 2007, 04:36:15 PM by Littlefield » Logged
Jonathan Wienke
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« Reply #3 on: July 07, 2007, 04:40:49 PM »
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First of all, your camera does not have a spot meter, so trying to use spot metering techniques will get you into far more trouble than anything. You're wasting your time even thinking about it. Learn how to read and interpret your histogram; every pixel in your sensor becomes a meter, and the histogram is an aggregation of those meter readings. When you shoot a test shot, you're basically taking several million ultra-precise spot meter readings over 100% of the frame, and the histogram maps the distribution of those readings so you know whether you should decrease or increase exposure. It's far faster than futzing with taking multiple spot meter readings, which you can't do anyway.
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Littlefield
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« Reply #4 on: July 07, 2007, 05:04:12 PM »
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First of all, your camera does not have a spot meter, so trying to use spot metering techniques will get you into far more trouble than anything. You're wasting your time even thinking about it. Learn how to read and interpret your histogram; every pixel in your sensor becomes a meter, and the histogram is an aggregation of those meter readings. When you shoot a test shot, you're basically taking several million ultra-precise spot meter readings over 100% of the frame, and the histogram maps the distribution of those readings so you know whether you should decrease or increase exposure. It's far faster than futzing with taking multiple spot meter readings, which you can't do anyway.
[a href=\"index.php?act=findpost&pid=127036\"][{POST_SNAPBACK}][/a]
You can do that with center or partial I am just wanting to know if he means setting it back to 0 when he meters on the other areas other then sky . I know you are trying to help but I was wanting an answer to this specific  question please.

When he says point the camera at the lightest area to see if it is more the +2 he does not mean setting the camera back to 0 right ? I mean you take a reading off sky by centering camera to 0 and then just move the camera to the shadows or lighter area to see how much difference there is without moving the neddle back to 0 ,the middle right ?
I know about exposing to the right and would probably chimp I just hate it when I do not fully grasp a procedure
Thanks
Don
« Last Edit: July 07, 2007, 05:59:03 PM by Littlefield » Logged
Jonathan Wienke
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« Reply #5 on: July 08, 2007, 02:42:49 AM »
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You can do that with center or partial I am just wanting to know if he means setting it back to 0 when he meters on the other areas other then sky . I know you are trying to help but I was wanting an answer to this specific question please.

Short answer: No, you cannot, and no. Center-weighted and partial CANNOT be used to do multi-spot metering accurately. You're measuring too much stuff at once other than the shadow or highlight in most cases, and the meter reading is meaningless and misleading. You can't change exposure settings between meter readings or the results are meaningless. You have to keep the camera settings the same for both the highlight and shadow readings, or you have no basis for comparison.

Long answer: You're asking which hammer to pound screws with. Attempting spot metering techniques with center-weighted or partial metering is going to give inaccurate and misleading results, because your meter reading isn't going to be limited to the bright or dark area you're trying to measure. You're always going to be measuring other irrelevant stuff as well, and that will skew your readings to the point where thy won't be helpful. For the technique to give any kind of meaningful results, you have to have an actual spot meter, otherwise you're trying to do brain surgery with a chain saw.

I happen to have 2 top-of-the-line professional Canon 1-series DSLRs, and have shot nearly 150,000 frames between them. You know how often I use multi-spot metering? Never. Why? Because in the time it takes to wave the camera around and take enough spot meter readings to be sure I've measured the brightest highlights and darkest shadows accurately, I could have pressed the shutter release once, glanced at the histogram, made any necessary adjustment, and captured a few properly-exposed frames.

Your camera does NOT have the tool you need to use the technique you're asking about. Your meter readings will be wrong fairly often, and as a result you WILL have exposure errors. You WILL take longer futzing around with multiple meter readings than you would pressing the shutter release and glancing at the histogram. Since the histogram is an aggregation of several million extremely narrow and precise spot meter readings (one from each pixel in the sensor) not using it is one of the most foolish things you can do when shooting digital.

Basic histogram interpretation is easy. Look at the right edge. If there is a spike, you have overexposed. The size of the spike is an indication how much you've overexposed. If there is a gap between the data and the right edge, you have underexposed. The gap width is an indication of how much you've underexposed. Yes, there are some exceptions and caveats, but that's the basic concept. Start with that, and re-read my article as you get more comfortable with the technique.

You'll get more accurate exposures faster than with any other technique once you learn this.
« Last Edit: July 08, 2007, 02:48:49 AM by Jonathan Wienke » Logged

Littlefield
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« Reply #6 on: July 08, 2007, 04:17:45 AM »
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Short answer: No, you cannot, and no. Center-weighted and partial CANNOT be used to do multi-spot metering accurately. You're measuring too much stuff at once other than the shadow or highlight in most cases, and the meter reading is meaningless and misleading. You can't change exposure settings between meter readings or the results are meaningless. You have to keep the camera settings the same for both the highlight and shadow readings, or you have no basis for comparison.

Long answer: You're asking which hammer to pound screws with. Attempting spot metering techniques with center-weighted or partial metering is going to give inaccurate and misleading results, because your meter reading isn't going to be limited to the bright or dark area you're trying to measure. You're always going to be measuring other irrelevant stuff as well, and that will skew your readings to the point where thy won't be helpful. For the technique to give any kind of meaningful results, you have to have an actual spot meter, otherwise you're trying to do brain surgery with a chain saw.

I happen to have 2 top-of-the-line professional Canon 1-series DSLRs, and have shot nearly 150,000 frames between them. You know how often I use multi-spot metering? Never. Why? Because in the time it takes to wave the camera around and take enough spot meter readings to be sure I've measured the brightest highlights and darkest shadows accurately, I could have pressed the shutter release once, glanced at the histogram, made any necessary adjustment, and captured a few properly-exposed frames.

Your camera does NOT have the tool you need to use the technique you're asking about. Your meter readings will be wrong fairly often, and as a result you WILL have exposure errors. You WILL take longer futzing around with multiple meter readings than you would pressing the shutter release and glancing at the histogram. Since the histogram is an aggregation of several million extremely narrow and precise spot meter readings (one from each pixel in the sensor) not using it is one of the most foolish things you can do when shooting digital.

Basic histogram interpretation is easy. Look at the right edge. If there is a spike, you have overexposed. The size of the spike is an indication how much you've overexposed. If there is a gap between the data and the right edge, you have underexposed. The gap width is an indication of how much you've underexposed. Yes, there are some exceptions and caveats, but that's the basic concept. Start with that, and re-read my article as you get more comfortable with the technique.

You'll get more accurate exposures faster than with any other technique once you learn this.
[a href=\"index.php?act=findpost&pid=127086\"][{POST_SNAPBACK}][/a]
Thanks Jonathan for making that clear you were very nice to explain  that in detail and I appreciate your patience . I have printed your info and tutorial out so I can read it good several times in a comfortable chair and get it to sink in right. Good luck in the Army .  
Don
« Last Edit: July 08, 2007, 04:27:24 AM by Littlefield » Logged
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