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Old Aug 15, 2006, 10:08 PM   #1
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how often do you use it in comparison to changing ISO or shutter speed?

if shooting in low light, you decrease the SS, or increase the ISO(800+),
action shots you increase SS and/or ISO.

so why bother with exp.comp?

if you do fiddle diddle with it, the ISO and SS change, thus you lose control.

I've noticed if even using -5 in bright sun, the photos are dark; +5 overexposed.

Thus, exp.comp _might_ be useful on P&S cameras with no manual aperture or shutter priority.
It is_very_ useful if shooting macro up close with the flash; if set to -2, prevents
over-exposure. Ifcourse, using zoom might do the same.

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Old Aug 15, 2006, 10:27 PM   #2
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romphotog wrote:
I've noticed if even using -5 in bright sun, the photos are dark; +5 overexposed.
That's what it's supposed to do. ;-)

It's not a substitute for making changes to things like ISO speed (which increases the sensitivity of a sensor to light, so that you can use faster shutter speeds or smaller apertures for the same exposure for a given lighting condition).

You use Exposure Compensation to give you a brighter or darker exposure.

Exposure Compensation lets you alter the way a camera's autoexposure/metering algorithms expose an image (brighten or darken it compared to the way the camera metered the scene). It's one of my most frequently used settings on most cameras.

A +EV value gives you a brighter exposure. The camera uses a slower shutter speed and/or larger aperture (smaller f/stop number) to get a brighter exposure, compared to what the camera's autoexposure/metering algorithms would have selected.

A -EV value gives you a darker exposure. The camera uses a faster shutter speed and/or smaller aperture (higher f/stop number) to get a darker exposure, compared to what the camera's autoexposure/metering algorithms would have selected.

If you're in Av Mode (Aperture Priority) and use Exposure Compensation, the camera will vary the shutter speed (since you're setting the aperture). If you're using Tv (Shutter Priority) mode and use Exposure Compensation, the camera will vary the Aperture (since you're controlling the shutter speed).

If you're in Auto (or other similar modes), the camera may vary aperture or shutter speed when you use Exposure Compensation. In low light, since your aperture is already wide open, it varies shutter speed if you use a -EV setting.

Correct Exposure comes down to the amount of light, the ISO speed, the shutter speed, and the aperture. A variety of combinations will produce identical exposure.

You only use Exposure Compensation if you want a brighter or darker image compared to what the camera's metering would normally give you in the same conditions.

An example of when you may want to use a +EV setting is for a backlit subject, where the subject would normally be much darker than the rest of the image. Since the camera has a limited dynamic range, it doesn't know that you want the dark subject exposed properly (at the expense of the rest of the image). So, you can make the darker subject brighter for correct exposure (which might cause the rest of the scene to be overexposed some).

If your subject is much brighter than the rest of the image, you may want to use a -EV setting for Exposure Compensation so that your subject is not overexposed (making the rest of the image darker, too).

The camera has a limited range of bright to dark that it can capture. So, it makes choices so that most of the iimage is correctly exposed, depending on your metering mode. Sometimes that may not be what you want. That's where exposure compensation comes in.

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Old Nov 15, 2006, 9:44 AM   #3
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I just want to re-phrase what Jim explained about exposure compensation, in "layman terms" that amateurs may understand easier:

When you are shooting someone standing in front of a bright background (eg. with the sunbehind his/her), the camera's light meter is "fooled" thinking the whole scene is very bright, therefore trying to reduce the amount of light hitting the sensor (or film if it is a film camera). The camera does not know the person is the subject of the shot, so by reducing the overall light level of the shot, the subject becomes too dark.

This is the situation when you have to compensate this shortcoming of the light meter by "increasing the light level" (+EV)of the subject so that it become brighter in the shot (the background, of course, will be too bright, but you don't really care about that).

This is the part where most amateurs misunderstand about exposure compensation, when they take the words "increasing the light level" literally. What you are doing is only to manipulate thereading of the light meter - you are NOT actually changing the lightcapturing sensitivity of the camera.

The reverse ("decreasing the light level" or -EV) is true when the background is much darker than the subject.

If you don't want to mess around with exposure compensation, you may get away with using "spot" metering (or "center weighed" metering), when you try to measure just the light level of the subject in the center. This may not work perfectly when the subject is too small, or the difference in light levels between the subject and background is extreme.

If youdo not makeexposure compensation in difficult lighting conditions, you may partly correct the exposure with photo editing software ("brightness" or "gamma correction") - the problem is, it is never as good as using exposure compensation in the first place, because what has been captured by the camera is what is in the picture. When you artificially boost dark areas, it may give you a "washed out" look with faded colors. If you tone down areas which are too bright, you may notrecover the original color which is drenched in the brightnessof the original picture. This relates to the "dynamic range" of the sensor that Jim described in his explanation.

Setting exposure compensation comes only with experience (practice) and trial-and-error - good thing this is the digital age so that we don't have to waste money developing many suboptimal pictures nowadays!
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Old Nov 15, 2006, 11:47 AM   #4
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Shooting in a snow scene requires about +1.0EV to keep the snow white and the subject better exposed. Otherwise the snow appears gray.
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Old Nov 15, 2006, 12:00 PM   #5
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I agree with JimC (like I often do). Exposure compensation is a *requirement* for me, if a camera doesn't have it I wouldn't buy it.

I use it in exactly the situation that others have described. I photograph wildlife, and when the subject is backlit, I have to adjust the exposure compensation so that the animal is properly exposed (and just accept that the background will be wrong.)

Until sensors get better at capturing a wider range of light to dark, this is a good way to get the shots you want.

Yes, I could use a spot meter (which I have on my 1D MkII N) and it would get it right in those situations... until I recompose without locking exposure. If I don't lock esposure it will get it wrong.

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Old Nov 15, 2006, 10:07 PM   #6
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Exposure compensation is best used referring to the histogram. And mostly to back your histogram from the right edge to keep from blowing highlights.

Spot metering is better in most backlight situations unless you have an excellent EVF so you can get good feedback of your EV correction. Unless your subject is very small in the scene, spot metering works fine and the shot will be metered for the face or whatever backlit subject you want properly exposed. Of course if the subject isn't in the center of the image you have to pre-meter using spot metering.

Bob is correct about the EV correction you want to use for snow. It is also sometimes useful for a very bright beach. But it is counterintuitive for some people to increase the exposure in snow. There are situations with a large black object in the scene where you might want to reduce the EV. Unless you understand why, it is probably better to use the snow or beach mode if the camera has one. Or pre-meter on your subject using spot metering.

Some cameras have a tendency to slightly overexpose and blow highlights. Many people always use something like - 0.7 EV to make sure the highlights aren't blown and make any adjustments necessary later in their image editing software.

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