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Photography Question 
Joseph M. Kolecki
BetterPhoto Member Since: 10/4/2005
 

METERING


Question... Can someone give me a good explanation on what metering is as well as the best way to do it? A couple of examples which I am unclear with... One, when I focus on a persons black suit coat, the background usally comes out blue or grey however when I meter on skin tones or a white dress, the background comes out vibrant and colorful. I am guessing this is all due to how I am metering my photo? I know white balance plays a roll in that too, but the focus area on my D70S depicts that... Anyway, can someone help me?


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9/14/2006 10:08:22 AM

 
Stefan Kanya   Hello Joseph,
the light meter interprets the measured value as 18% grey and the camera sets the exposure according to that.

You have to keep in mind what kind of metering you use on your cam (spot, center weighted or matrix).

E.g. if you use center weighed and there is a black suit coat in the center, the cam tries to exposure the black suit coat as 18% grey coat. As this is a bit to light all other things will become a little bit to light too.

If in the center is a white dress it will be the oder way round. Again tries the cam to exposure the dress as 18% grea, which is too dark. Therfore all sourounding things will become a little bit too dark.

If you have a pictuer which is as an average over the whole picture not close to 18% grey you have to adjust manually.
A good procedure for that cases is to exposure for the sky - if it is a blue one. In most cases the exposure will be fine.

Best regards,
Stefan


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9/16/2006 4:52:17 PM

 
Donald R. Curry
BetterPhoto Member Since: 3/2/2006
wildlifetrailphotography.com
  Joesph,

There is a good way to overcome this issue. If you have spot meter on your camera, you can spot meter the black coat at a minus 2 exposure. The black coat will be black and everything else in the photo will come out right as long as it is within exposue limits of the camera (or film. Another example is snow. You can spot meter snow at a +2 for it to be perfectly white or a +1.5 to give it a little texture. A good rule of thumb is if it is the shade of the palm of your hand it would be spot metered at a +1. You can also find something in the photo in the same light as the main subject that is neutral, like green grass, a medium grey rock etc, and meter it. Set your metering for the photo at that level.You can judge the in between exposures and experiment a little. It is a good concept. I have used it and it works. You have to know the exposure limits of your film or camera. Typically it is a range of 5.


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9/16/2006 5:16:48 PM

 
Donald R. Curry
BetterPhoto Member Since: 3/2/2006
wildlifetrailphotography.com
  Joesph,

I forgot to mention that the thumbnail photo to the right was spot metered on the yellow flower at +1.


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9/16/2006 5:36:10 PM

 
Donald R. Curry
BetterPhoto Member Since: 3/2/2006
wildlifetrailphotography.com
  Sorry, to the left.


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9/16/2006 5:49:25 PM

 
Mark Feldstein
BetterPhoto Member Since: 3/17/2005
  As Stefan mentioned, meters are essentially gray meters and average reads a scene as though everything in them was that particular shade of gray. That's ok for a lot of situations, but depending on what's really going on in your scene, it could lead to inaccuracies. Sooooooooooo, the best way to do this, in a sense, is what Don mentioned but overall, you need to learn how to interpret the gray reading that your meter is giving you to produce accurate, consistent exposures.

It's not too difficult really, but takes practice and a bit of reading material. One book I recommend to students is called (oddly enough) "The Hand-Held Exposure Meter Book" by Bob Shell, among others. It used to be published by, and available at, Sekonic's web site, but also try Amphoto as well as Barnes and Noble.

Even if you don't have a hand held meter, it explains the differences between in-camera meters and hand held, and how to use them more accurately under a lot of common lighting situations, including the ole blinding white snow storm and getting pictures with severe exposure shortcomings.
Take it light.
Mark


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9/17/2006 10:18:06 AM

 
Alan N. Marcus   Hi Joseph,
How to meter and how to interpret exposure data is one of the most elusive issues facing photographers.

First some trivia:
Light meter science is based in large part upon a neutral (not color biased) gray placard, middle gray in tone. This shade is roughly “battleship gray”. The theory goes: The typical scene integrates to middle gray if viewed as a totally diffused and out-of-focus image. Now shine a light on this placard; it reflects 18% and absorbs 82% of the light.
The hue is the middle of the scale of the typical black and white film. It is also the middle tone found in the black and white print.

The theory:
Chosen because when taking a picture of the gray card, if the camera exposure is correct and the film is correctly developed, the resulting image of the card on the film is an exact match (i.e. the same shade) of the original card (plus film base density). Now if a print is made from this negative, and the technique used causes the print paper to be properly exposed and correctly developed, the image of the gray card on the finished print will exactly match the original card. The 18% target shade is the only tone known that reproduces the same as the original on both the negative and the print.

Gray card exposure theory:
Place a gray card in the scene and light it the same as the principal subject.
Take a close-up reflective meter reading off the card.
Set camera exposure exactly as indicated.
Resulting negative reproduces exactly the same shade as original card.
Print this negative and the resulting image of card is an exact match of the original card Photo science says “If the gray card is correctly reproduced, than all other tones in the scene will be rendered correctly”.
Theory carries over to slide film and digital without a flaw.

The gray card is an important tool, however pitfalls abound mainly due to mishandling via placement and slant or due to atypical subjects. Many photographers instead, swear by the incident meter. This instrument features an opaque spherical diffuser covering the sensor. A reading is taken from the subjects’ prospective, looking back at the camera.
The sphere diffuser integrates the subject to gray. This method avoids carrying a gray card around, and the readings are exactly the same as a reflective gray card reading. Incident reading eliminates many of the pitfalls.

Modern film and digital cameras have an effective built-in meter and draw on chip logic to provide feedback setting the camera. Additionally, mode settings add even more logic. Modern cameras set themselves and the logic is excellent. Don’t worry yourself -- just shoot and have fun.

Alan Marcus
ammarcus@earthlink.net


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9/17/2006 10:49:18 AM

 
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