Metering

[Emerana]

I have been reading about my camera (XTi) and photography but for some reason every time I read about metering my brain stops collecting information. Could I ask the photo gurus for a little help explaining where you meter? How do you know? When and why do you compensate for the exposure?

:hail:

 

[Mav]

Just look at your LCD screen and RGB historgrams (does the XTi do that?) If you're blowing highlights or the photo looks too bright, reduce exposure. Or if you're dropping shadows or the photo looks too dim, increase exposure. If you're blowing both highlights and shadows then you have a really contrasty scene. Manually lower the contrast on the camera, or if appropriate, try using a flash to fill in the shadowy areas. If the histograms are tight and sorta bunched up in the middle and your photo looks a bit flat, try manually increasing the contrast.

99% of the time I just use matrix metering on my Nikon, but if I have a lighter face, a dark shirt, and then a medium toned background it can confuse the heck out of the matrix metering algorithm and the exposure can go all over the place. In that case I use center weighted or spot metering. Not sure what Canon calls it.

 

[nicfargo]

Metering used to refer to using a light meter. With a lot of digital cameras, and some film cameras, oftentimes there's a built in meter. When looking through the view finder on you XTi, you'll notice at the bottom a line that looks something like this:
-----------------------
-2 -1 0 1 2

(these numbers should be spaced out evenly...stupid interweb doesn't keep my spacing when I post!)

There will be a bar that moves along this line when you change settings on your camera. Usually 0 is where you want your bar to be because that means exposure is correct (at least according to your camera...which can be off at times). -2 is underexposed and +2 is overexposed. You can also use a histogram on the XTi (assuming it has one).

 

[Emerana]

Thanks guys. I do have a histo and the blown out parts blink (as if to taunt me lol) and i know how to set my exposure. I just dont know where in the photo I am supose to point the camera to get the reading. the brighter areas, the darker, the center?

i take alot of photos trying to get the right balance if it is a contrasty. Are there rules that make it easier or do you just adjust until you get it rigt?

 

[Big Mike]

As mentioned, digital offers us a new method of metering. By viewing the histogram after a shot, we can see the results, make adjustments and shoot again. A good rule of thumb is to 'expose to the right'...meaning that you want your histogram to be biased to the right, but without clipping (blowing out) the highlight detail.

Back to metering. The basic premise that you need to understand is that the camera's meter is set to give you an exposure for 18% grey (mid tone). It has to be set for something, so that is it. This means that when you meter a scene that is bright, the meter will give you settings to turn that bright scene into a mid tone. Same with a dark scene...the meter always wants to make it middle grey.
Realistically, most scenes will have a mix of tones and the meter reading will give you an exposure value that works well. That's why most people can get by without know anything about metering.

However, to get more accurate results, you can think about the metering and compensate for what the meter is doing. For example, if you are taking a photo with a lot of snow, it will probably be very bright. The camera's meter will want to turn it into mid grey because it doesn't know that it's snow. The result will be that the snow looks grey (underexposed). The solution is for you to add positive exposure compensation. Knowing just how much to add...comes from experience. For snow it might be two stops, give or take.
The same applies for dark scenes...the camera tries to make it grey so you would want to subtract exposure.

That is metering with a reflected light meter (the type in your camera). You could use a hand held incident meter and just meter the light...this is more accurate.

 

[fatsheep]

I've got a related question. My camera (sig) handles light metering in its "Photometry" menu. There are three options: average, spot, and multi. I understand the first two but is multi center-weighted or matrix?

From the manual:

"MULTI (Pattern): Light metering where the camera assesses the scene and selects the correct exposure?"

It sounds like matrix to me but I thought I'd ask to make sure.

 

[Garbz]

average = centre weighted, multi = matrix.

 

[Helen B]

average = centre weighted, multi = matrix.

Isn't 'average' for the S700 an average rather than a centre-weighted reading, or have I misunderstood?

"Light metering where an average value for the entire image is used."

Best,
Helen

 

[Sideburns]

If you wanna know where to meter...Bryan Peterson's book "understanding exposure" is somewhat helpful for outside.

Usually, an 18% graycard is what you want.

 

[fatsheep]

Isn't 'average' for the S700 an average rather than a centre-weighted reading, or have I misunderstood?

"Light metering where an average value for the entire image is used."

Best,
Helen

Yea I was under that impression too. Also, the symbol for average on the camera is too brackets like this: [ ]

There isn't anything in the center and I would think there would be if it was center-weighted...