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05-10-2009, 08:05 PM   #1
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exposure compensation

Hey there i recently realized that while I often use exposure compensation i don't actually know what the camera is changing in order to get these different results.

As far as i have noticed changing the exposure compensation does not affect the shutter speed or aperture, nor does it change the ISO setting, so what is being changed?

05-10-2009, 08:33 PM   #2
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The camera's logic on which of those it will change will vary according to the scenario, and what your setup is, it has to change one of those items to do the compensation - either ISO, Aperture, or Shutter speed has to change in order to change the exposure.

For instance if you are in Av mode, the camera can't change the Aperture - it considers it fixed... Now if you have ISO set to a specific value (say ISO 200) rather than Auto-ISO, the camera will consider that fixed as well and so will compensate the exposure with the shutter speed.

However if OTOH you have Auto ISO set to the range from 100-1600, and you are using Av mode, the camera may decide to alter the ISO rather than the shutter speed (for instance the camera will attempt to keep the shutter speed above a certain value to try to keep camera-shake from harming your pictures.
05-10-2009, 08:36 PM   #3
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It's a very clever algorithm that detects which setting you are currently looking at in the viewfinder, and then changes one of the other two so you won't notice.
05-11-2009, 02:33 AM   #4
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What is exposure compensation?

I'm only aware of exposure value - EV.

What am I missing?

05-11-2009, 04:21 AM   #5
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Same thing, different words.
05-11-2009, 07:58 AM   #6
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Nope, EC and EV are NOT the same thing.

Exposure value - Wikipedia, the free encyclopedia

Exposure compensation - Wikipedia, the free encyclopedia

In a nutshell, the camera' meter determines an EV, but if you select EC, the camera will deviate from its selected EV...

Clear as mud?

In Av mode, multi-segment metering, you select f/4, ISO200 and point the camera at a scene. The camera picks 1/500. So f/4, ISO200, 1/500s gives you a particular EV. You disagree with the camera and would like the shot to be one stop brighter, so you select +1 EC, the camera will now shoot at 1/250s, which would give you a different EV (one more EV than what the camera "wanted" to use)

I'm too busy to calculate the actual EVs, but the formula should be on that link I posted above.

QuoteOriginally posted by flyer Quote
Same thing, different words.
05-11-2009, 10:50 AM   #7
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EV = units of measurement used by exposure compenation.

Seen in this way, EC is like "speed", EV is like "miles per hour". EC is *what* we measure or control, EV are the units we express it in.
05-11-2009, 11:45 AM   #8
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Put another way:

EV is an absolute value representing the amount of light reflected by a given scene.

EC is a settable value that lets you tell the camera to expose over or under the measured EV.

05-11-2009, 01:02 PM   #9
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QuoteOriginally posted by OregonJim Quote
Put another way:

EV is an absolute value representing the amount of light reflected by a given scene.

EC is a settable value that lets you tell the camera to expose over or under the measured EV.
In other words "exposure compensation" (EC) is accomplished by manipulating "exposure values" (EV) as expressed in EV units.

The term "exposure compensation" seems to me to be an over-inflated term that any photographer does intuitively in the normal course of taking photos.

For instance I use five different fixed aperture lens' f/5, 6.2, 7.0, 8.3 and f/12 in AV mode. Not a one of them gives me a "normal" exposure if set to a EV value of 0. All of them must be calibrated to the camera's exposure system by using an EV value of something other than an EV of 0. For instance one must be set to an EV value of -1 and another to an EV value of +.7. It never occurred to me that I was performing "exposure compensation". BTW EV values can be set on my 1958 Rollie.

Wikipedia says it well:
"In photography, some cameras include exposure compensation as a feature to allow the user to adjust the automatically calculated exposure. Compensation can be either positive (additional exposure) or negative (reduced exposure), and is commonly available in third- or half-step[1] increments, usually up to two or three steps in either direction; some digital cameras allow a greater range. Camera exposure compensation is commonly stated in terms of exposure value (EV); 1 EV is equal to one exposure step."

Interestingly the term "exposure compensation" is never used in the K20D manual except in reference to the use of flash.
05-11-2009, 03:10 PM   #10
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QuoteOriginally posted by wildman Quote
Interestingly the term "exposure compensation" is never used in the K20D manual except in reference to the use of flash.
The Pentax manuals call it "EV compensation".
05-11-2009, 04:44 PM   #11
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QuoteOriginally posted by egordon99 Quote
Nope, EC and EV are NOT the same thing.

Exposure value - Wikipedia, the free encyclopedia

Exposure compensation - Wikipedia, the free encyclopedia

In a nutshell, the camera' meter determines an EV, but if you select EC, the camera will deviate from its selected EV...

Clear as mud?

In Av mode, multi-segment metering, you select f/4, ISO200 and point the camera at a scene. The camera picks 1/500. So f/4, ISO200, 1/500s gives you a particular EV. You disagree with the camera and would like the shot to be one stop brighter, so you select +1 EC, the camera will now shoot at 1/250s, which would give you a different EV (one more EV than what the camera "wanted" to use)

I'm too busy to calculate the actual EVs, but the formula should be on that link I posted above.
The way Wildman stated his post made me believe that this was the answer he was looking for. I know that EV and EC are not the same thing, but in this context, it was what Wildman was looking for.
05-11-2009, 10:03 PM   #12
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QuoteOriginally posted by flyer Quote
The way Wildman stated his post made me believe that this was the answer he was looking for. I know that EV and EC are not the same thing, but in this context, it was what Wildman was looking for.
Kinda like AV, SV and TAV, all are adjustable just like EV -C

I understand what you were refering to!
05-11-2009, 10:52 PM   #13
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QuoteOriginally posted by wildman Quote
The term "exposure compensation" seems to me to be an over-inflated term that any photographer does intuitively in the normal course of taking photos.

For instance I use five different fixed aperture lens' f/5, 6.2, 7.0, 8.3 and f/12 in AV mode. Not a one of them gives me a "normal" exposure if set to a EV value of 0. All of them must be calibrated to the camera's exposure system by using an EV value of something other than an EV of 0. For instance one must be set to an EV value of -1 and another to an EV value of +.7. It never occurred to me that I was performing "exposure compensation".
I wouldn't call it "normal". You are doing it because of a design deficiency specific to the K10/K20 metering system. These cameras do not meter correctly with lenses that don't communicate aperture information. That's why you have to manually compensate.

On my K200 and *ist DL, EC is set to zero regardless of the lens/aperture in use. The metering is always accurate. I only change EC if I'm in Av mode and I want to intentionally alter the exposure (snow/sand, backlit subject, etc). That's the way it's *supposed* to work.

Last edited by OregonJim; 05-11-2009 at 10:57 PM.
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