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Archive 2008 · Exposure Compensation -- Why?

alfarmer
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p.1 #1 · Exposure Compensation -- Why?

Ok, I just don't get it and nobody I know can explain it. So hopefully some FM expertise will help.

What's the point to having an Exposure Compensation setting? Why not simply adjust the ACTUAL exposure? Bracketing has a clear and obvious value, but dialing in some constant offset does nothing more than complicate the mental process during shooting. Why would anyone EVER want/need to do that?

Thanks,
ALF

Sep 05, 2008 at 02:41 AM

Pixel Perfect
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p.1 #2 · Exposure Compensation -- Why?

What you say is sort of true for a static subject in nonchanging light, but let's say you are shooting a moving subject that has a quickly changing exposure. You do not have time to set a correct exposure, but it maybe you don't want to blow white features and you know that say if the background is dark, if you dial in some negative EC say -2/3 stop, and shoot in evaluative, you can be pretty confident the highlights will be preserved. You could not hope to keep changing exposure to keep up in fast action with variable lighting.

Sep 05, 2008 at 02:46 AM

JDSA
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p.1 #3 · Exposure Compensation -- Why?

What? What actual exposure? Say your subject is a black man in a white jacket walking in the noon-time sun. You dial in a ton of exposure so you can get his facial features at the expense of the blown out jacket. Now he walking into the shade. You adjust.

You can do the olden-days alternative. Shoot completely manual. Take a meter reading before each shot. Set the camera and go (but don't cheat and look at the monitor).

Sep 05, 2008 at 02:57 AM

Cicopo
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p.1 #4 · Exposure Compensation -- Why?

It's the right tool for the job, in the simplest of terms. Too light reduce exposure, too dark increase it; OR use it to match YOUR idea of a correct exposure to your base settings, which is what I do. For my personal use of a digital camera that instantly shows me the results it's a Godsend. Way back in film days I either had to bracket, or go into my darkroom and cut off my test stip, process & evaluate. EC is my very best friend thank you.

Sep 05, 2008 at 02:58 AM

pixelman
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p.1 #5 · Exposure Compensation -- Why?

Become one with your f stops grasshopper and all will be revealed.

Sep 05, 2008 at 03:01 AM

designguy
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p.1 #6 · Exposure Compensation -- Why?

alfarmer wrote:
Ok, I just don't get it and nobody I know can explain it. So hopefully some FM expertise will help.

What's the point to having an Exposure Compensation setting? Why not simply adjust the ACTUAL exposure? Bracketing has a clear and obvious value, but dialing in some constant offset does nothing more than complicate the mental process during shooting. Why would anyone EVER want/need to do that?

Thanks,
ALF

sounds to me like you already have it figured out

Sep 05, 2008 at 03:07 AM

nathanlake
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p.1 #7 · Exposure Compensation -- Why?

I usually shoot AV in order to closely control the DOF. That means the shutter is automatically set and if it is blowing out whites I will compensate down 1/3 stop or so to save the highlights. This happens all the time with a backlit subject.

Edited on Sep 05, 2008 at 03:22 AM

Sep 05, 2008 at 03:22 AM

freaklikeme
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p.1 #8 · Exposure Compensation -- Why?

I'm a little confused about exposure compensation myself. Is in-camera exposure compensation any different than the exposure comp you can adjust in the raw conversion using PS or DPP (or any other converter, I assume)? If so, then what's the difference between using exposure comp and dialing in a higher or lower ISO, since they're both just software-based emulations of of what your image probably looked like had you made some physical change? Is it that exposure comp allows for a more finite control?

Edited on Sep 05, 2008 at 03:25 AM

Sep 05, 2008 at 03:24 AM

dan9
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p.1 #9 · Exposure Compensation -- Why?

Recommend you read up on the history of camera metering, and also on the speed rating of film.

"Exposure compensation" is a misnomer in many ways (which is not uncommon in photography terminology.)

For each photograph there is only one "exposure" ( = time x light intensity reaching sensor), unless of course one is doing multiple exposures on one frame (of film, or one digital file composite.)

"Compensation" has as one of its denotations the meaning of a particular adjustment in the development of a piece of film.

However, since you are likely using only digital we can skip that part...

Today, when most people say they are "compensating" they are really saying that they are aware of a particular trait of their exposure meter + exposure algorithm (within the computer that runs inside your automated camera) which, when used in certain situations, will not give them what they desire. So, when then encounter a situation in which they know their meter+camera program will fail them, they (having learnt by experience) tell the embedded computer to bias the exposure from the meter reading (in one direction or another.)

Sep 05, 2008 at 03:26 AM

freaklikeme
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p.1 #10 · Exposure Compensation -- Why?

JDSA wrote:
What? What actual exposure? Say your subject is a black man in a white jacket walking in the noon-time sun. You dial in a ton of exposure so you can get his facial features at the expense of the blown out jacket. Now he walking into the shade. You adjust.

I don't understand how exposure comp would save you in this scenario. Does it somehow compensate for only the highlights or shadows? How does it know which to compensate for?

Sep 05, 2008 at 03:31 AM

dan9
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p.1 #11 · Exposure Compensation -- Why?

freaklikeme wrote:
JDSA wrote:
What? What actual exposure? Say your subject is a black man in a white jacket walking in the noon-time sun. You dial in a ton of exposure so you can get his facial features at the expense of the blown out jacket. Now he walking into the shade. You adjust.

I don't understand how exposure comp would save you in this scenario. Does it somehow compensate for only the highlights or shadows? How does it know which to compensate for?

The given example needs more elaboration....

Since in digital the issue is blowing the highlights (similar to slide film, and the opposite of color print film), in this case one must first determine if you have to sacrifice the white coat or not. If you spot meter off of the white jacket, then the black man's face, it is likely that the difference will not be so great that today's DSLRs would fail totally (unlike say slide film.)

A traditional approach in the given example would go like this: Say you are using the Av program (because DOF is most important to you.) You spot meter off the white jacket, then dial in +2 to +2 and 1/3 stops of "exposure compensation" (which in this case will change the shutter speed), since a spot reading on a white jacket will end up giving you a grey jacket if you expose at the given meter reading.

THE ABOVE METHOD IS THE SAME WHETHER IN SHADE OR SUN. E.g., if you spot meter off the jacket while the subject is in the shade, you will still dial in the +2 compensation. If you don't, then the white jacket will turn out grey (and the ebony skin will turn out to be very dark and noisy (in digital)).

Sep 05, 2008 at 04:15 AM

EB-1
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p.1 #12 · Exposure Compensation -- Why?

Normally I only use EC if the camera has a bias one way or another compared to how I usually meter. For example I have to set the D80 to -1/3 or even -2/3.

EB

Sep 05, 2008 at 04:28 AM

mh2000
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p.1 #13 · Exposure Compensation -- Why?

maybe I missed this... but, the camera meters to make your scene neutral gray, no matter what you put in front of it. If you are shooting a snow scene, the camera will render it gray... which you know is wrong, you set EC to correct for this... say +2 or there abouts, the scene will now be closer to a snow white scene... same goes for black men in a coal mine... on minus this time. The camera doesn't know what it is shooting... you do.

Sep 05, 2008 at 04:31 AM

alfarmer
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p.1 #14 · Exposure Compensation -- Why?

Hmm. I'm not sure the point of my question is getting through to most responders, so let's assume always shooting in Aperture priority mode for a second.

When shooting snow or a white suite in daylight, I could certainly adjust exposre by +2 or -2. But it's MUCH easier and quicker to dial the big fat knob that adjusts shutter speed.

And this leads to the one scenio not mentioned thus far, and the one case I can think of for my personal usage of Exposure Compensation -- low light settings where adjusting the shutter speed or ISO might result in unacceptable blur or noise.

For "fast action" shooting, one person said it's quicker to set exposure comp. than to adjust anything else -- but I still say changing shutter speed or ISO is faster. Either way, if you need to make lighting/exposure adjustments up & down the court it will be difficult. That's ONE reason why some folks carry multiple cameras.

So with the specific example of shooting in Aperture priority mode, why would one rely on the Exposure Comp. function instead of simply cranking the shutter speed? I can't think of many.

EB's response was also educational and I tend to agree. If a camera has exposure issues in, say, Program mode (what I put it in when I hand it to someone else to take a picture), then a constant adjustment may be warranted. I wasn't thinking in terms of compensating for the technology itself with a little "Human AI", but it makes sense.

All I know is in 8+ years of digital photography of one kind or another, I've never had need of EC settings. Must be lucky with gear. :-)

ALF

Sep 05, 2008 at 05:39 AM

dan9
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p.1 #15 · Exposure Compensation -- Why?

alfarmer wrote:

So with the specific example of shooting in Aperture priority mode, why would one rely on the Exposure Comp. function instead of simply cranking the shutter speed? I can't think of many.

If you are want to "crank" the shutter speed, why are you working in Av priority mode? Sounds like you are causing yourself unnecessary confusion here.

If you want to control time per your wishes, shoot in Tv mode or M.
If you want to control aperture per your wishes, shoot in Av mode or M.

Use exposure compensation when you want to work in only one mode (Tv, Av, or P), and yet want to add your natural (not artificial) human intelligence to the rather limited skills of the in camera metering algorithm.

Sep 05, 2008 at 06:32 AM

reggie747
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p.1 #16 · Exposure Compensation -- Why?

ALF,

I may be missing something here but your last post says "assume always shooting in Aperture Priority" yet you make 4 references to shutter speed adjusting ??
This line in particular has got me..

So with the specific example of shooting in Aperture priority mode, why would one rely on the Exposure Comp. function instead of simply cranking the shutter speed? I can't think of many.

What gives here

Sep 05, 2008 at 06:44 AM

freaklikeme
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p.1 #17 · Exposure Compensation -- Why?

dan9 wrote:
The given example needs more elaboration....

Since in digital the issue is blowing the highlights (similar to slide film, and the opposite of color print film), in this case one must first determine if you have to sacrifice the white coat or not. If you spot meter off of the white jacket, then the black man's face, it is likely that the difference will not be so great that today's DSLRs would fail totally (unlike say slide film.)

A traditional approach in the given example would go like this: Say you are using the Av program (because DOF is most important to you.) You spot meter off the white jacket, then dial in +2 to +2 and 1/3 stops of "exposure compensation" (which in this case will change the shutter speed), since a spot reading on a white jacket will end up giving you a grey jacket if you expose at the given meter reading.

THE ABOVE METHOD IS THE SAME WHETHER IN SHADE OR SUN. E.g., if you spot meter off the jacket while the subject is in the shade, you will still dial in the +2 compensation. If you don't, then the white jacket will turn out grey (and the ebony skin will turn out to be very dark and noisy (in digital)).

No, it's obviously my question that requires further explanation. I'm not confused about compensating for different lighting in your exposure. I'm confused about how the function labeled "exposure compensation" within the digital camera could save you anything in the scenario described. If you have proper exposure on the face, then what does that specific function of the camera save you?

Are you saying the exposure compensation (the camera function) actually changes your shot settings? It lengthens the shutter speed in this scenario?

Edited on Sep 05, 2008 at 07:47 AM

Sep 05, 2008 at 07:44 AM

dhphoto
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p.1 #18 · Exposure Compensation -- Why?

freaklikeme wrote:

No, it's obviously my question that requires further explanation. I'm not confused about compensating for different lighting in your exposure. I'm confused about how the function labeled "exposure compensation" within the digital camera could save you anything in the scenario described. If you have proper exposure on the face, then what does that specific function of the camera save you?

Are you saying the exposure compensation (the camera function) actually changes your shot settings? It lengthens the shutter speed in this scenario?

Yes, of course.

Exposure compensation alters the camera's attempt at correct exposure (i.e. to render 18% grey) by an amount decided by the user.

The example given is not a good one as frankly there is no free lunch in this situation and the contrast range is just going to be beyond what the camera can handle, you need to lower the contrast, but here's another: If I want to photograph caucasian skin in daylight I know from experience I'm going to want +2/3 of a stop to render the skin the tone I want. If the overhead conditions change and the light becomes brighter or less bright it doesn't matter, as my exposure will continue to be +2/3 of a stop over the camera's default reading. It works very well indeed.

In answer to your question about whether it matters if you adjust exposure in-camera or in post processing yes it does, very much so. Beyond a very small exposure latitude in a RAW file (and none in a jpeg) any post processing will be detrimental to the file. It is just as vital to get exposure right in digital as it was with reversal film.

David

Sep 05, 2008 at 08:08 AM

Cableaddict
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p.1 #19 · Exposure Compensation -- Why?

alfarmer wrote:
When shooting snow or a white suite in daylight, I could certainly adjust exposre by +2 or -2. But it's MUCH easier and quicker to dial the big fat knob that adjusts shutter speed.

Alf, I think you make a pretty good point, but here's a maybe:

In AV mode, it's true you can use the big wheel to adjust the shutter speed, and it's the same result. However, you have to do this every time you take a shot. Suppose you are shooting a moving target, maybe a rock singer wearing a white shirt under a bright spotlight (a very tough exposure situation) and are also changing DOF a lot? EC is a one-time deal.

Same goes for some alternative lenses: I have a few that seem to "fool" the exposure meter, no matter what the subject. I know that with those lenses I have to set compensation, if I want to use the 5D's LCD meter as an exposure guide.

Of course, Canon in their infinite wisdom made EC as difficult as MLU, so really it's not more convenient. Also, using the big wheel gives more control over each shot, without having to navigate that bloody menu maze. Kind of a toss-up.

Edited on Sep 05, 2008 at 08:57 AM

Sep 05, 2008 at 08:55 AM

Beni
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p.1 #20 · Exposure Compensation -- Why?

Don't even begin to understand the question. If you are using Av mode then you are expecting the camera to choose the shutter speed AUTOMATICALLY, EC makes sure that the choice is correct. What Alf is asking apparently is why not shoot in manual. I'll tell you why, we don't all have time to meter, apply to the camera and shoot. When I shoot a wedding with a camera in Av I choose an aperture of f1.8 for example and expect the camera to do the rest. Because canon metering sucks in difficult lighting I have to help it along with EC. It's still a few worlds away from having to shoot everything in manual.

Sep 05, 2008 at 09:10 AM

Mike Farren
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p.1 #21 · Exposure Compensation -- Why?

reggie747 wrote:
ALF,

I may be missing something here but your last post says "assume always shooting in Aperture Priority" yet you make 4 references to shutter speed adjusting ??
This line in particular has got me..

So with the specific example of shooting in Aperture priority mode, why would one rely on the Exposure Comp. function instead of simply cranking the shutter speed? I can't think of many.

What gives here

Yeah this has got me bewildered too. As far as I know the only way to alter the shutter speed manually while in Av mode is to use exposure compensation.

Sep 05, 2008 at 10:07 AM

snurresprett
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p.1 #22 · Exposure Compensation -- Why?

alfarmer wrote:
Hmm. I'm not sure the point of my question is getting through to most responders, so let's assume always shooting in Aperture priority mode for a second.

When shooting snow or a white suite in daylight, I could certainly adjust exposre by +2 or -2. But it's MUCH easier and quicker to dial the big fat knob that adjusts shutter speed.
...
So with the specific example of shooting in Aperture priority mode, why would one rely on the Exposure Comp. function instead of simply cranking the shutter speed? I can't think of many.

Err... when shooting in Aperture Priority mode, you are basically telling the camera to set the shutter speed as it sees fit in order to achieve the metered exposure. It is not possible to explicitly set shutter speed yourself in AV mode. If you dial in exposure compensation, the camera will use a correspondingly slower or faster shutter speed than it would based purely on the meter. Or, to put it another way: When you "simply crank the shutter speed" in AV mode, you are in fact using exposure compensation!

So I don't think your question makes much sense at all, frankly. The purpose of having exposure comp available is of course simply that the meter isn't always right... but I guess we all know that already.

Sep 05, 2008 at 10:12 AM

Fred Relaix
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p.1 #23 · Exposure Compensation -- Why?

Mike Farren wrote:
reggie747 wrote:
ALF,

I may be missing something here but your last post says "assume always shooting in Aperture Priority" yet you make 4 references to shutter speed adjusting ??
This line in particular has got me..

So with the specific example of shooting in Aperture priority mode, why would one rely on the Exposure Comp. function instead of simply cranking the shutter speed? I can't think of many.

What gives here

Yeah this has got me bewildered too. As far as I know the only way to alter the shutter speed manually while in Av mode is to use exposure compensation.

This is correct, if you adjust EC, your shutter speed will vary while your exposure should not.
EC is also very important if you use spot metering for exposure because (in my case at least) I would often spot in the shadow where I want to get details (then I would go EC between -1 and -2), or spot meter in the highlights (ie +1 to +2) to not blow them. Also for night pictures, if you want to take a picture that looks like what you see with your eyes, (again in Av mode) you absolutly need to get your EC down to -1 to -2. I aften wish my 5D would go to +/-3 or even +/-5.

Sep 05, 2008 at 10:19 AM

Steve Spencer
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p.1 #24 · Exposure Compensation -- Why?

Let me take a crack at this. Let's say I am shooting birds in AV mode to control aperture so that I have just the depth of field that I want in the shot. This means the camera will select the shutter speed and I will select the aperture and ISO. I know from either experience or perhaps from looking at the histogram from a previous shot, however, that the shutter speed that the camera will select will be too fast leaving the bird underexposed. To get a longer exposure I dial in positive exposure compensation which will cause the shutter speed to be longer and the bird to be better exposed. I could of course do exactly the same thing by flipping to manual mode and changing to a longer shutter speed. If the the light is pretty consistent then the two methods are six of one half a dozen of another. If the light is changing a fair bit, however, then AV mode can be nicer. Let's say the sun is going in and out from behind the clouds and changing the brightness of the scene a fair bit. With AV I only need to change the exposure compensation once and the setting will work whether the sun is at full brightness or behind a cloud. With manual I will have to reset the shutter speed each time the sun goes behind the cloud and each time it come back out. I hope this makes sense.

Best wishes,

Steve

Sep 05, 2008 at 10:37 AM

astrolucida
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p.1 #25 · Exposure Compensation -- Why?

alfarmer wrote:
Hmm. I'm not sure the point of my question is getting through to most responders, so let's assume always shooting in Aperture priority mode for a second.

When shooting snow or a white suite in daylight, I could certainly adjust exposre by +2 or -2. But it's MUCH easier and quicker to dial the big fat knob that adjusts shutter speed.

Well, this is exactly how exposure compensation is changed in Canon DSLRs! So you are using exposure compensation. When the aperture is fixed in the Av mode, the only way to change the effective exposure is to change the shutter speed. Thus, e.g. dialing in +1 for exposure compensation (you can see it in the viewfinder, too), results in doubling the exposure time.

alfarmer wrote:
And this leads to the one scenio not mentioned thus far, and the one case I can think of for my personal usage of Exposure Compensation -- low light settings where adjusting the shutter speed or ISO might result in unacceptable blur or noise.

No, exposure compensation does not help that because it changes those exact parameters, resulting in exactly the same results as if you had manually selected the same settings. There is no exposure compensation function like the one you seem to be thinking of.

Let's summarize:
- exposure settings consist of aperture, shutter speed and ISO,
- for ISO you can either pick the value or use Auto (in some cameras),
- you can set both the aperture and the shutter speed if you use M mode,
- you can set the aperture in Av mode and the camera sets the shutter speed,
- you can set the shutter speed in Tv mode and the camera sets the aperture,
- the camera will set both shutter speed and aperture in P mode.

When the camera decides some of the values, it is basing that decision on the built-in exposure meter. If you want to change that decision, by a relative value, you dial in exposure compensation (-2 to +2 with 1/3 stop steps). If you want to set the absolute values, you use M mode. In that case, you will see, in relative terms, how the camera would set the exposure values, in the viewfinder.

Edited on Sep 05, 2008 at 11:52 AM

Sep 05, 2008 at 11:50 AM


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