Exposure Compensation How to use?!?!

[RbrtPtikLeoSeny]

Alright, I just got my 20D a few days ago and I'm trying to learn how to shoot full manual, and or using AV and Tv, problem is, I don't understand this -2-0-+2 exposure thing..... first of all, when shooting manual sometimes I get it perfectly at 0, and the image still comes out ****ty, and then I set the settings so it's way past -2 and it comes out great! Having trouble with this...

and, when do I need a negetive exposure, when do I need a positive? when do I need a perfect 0?

In AV mode I notice the scroll wheel lets me play with the exposure thingy, and automatically adjusts the shutter speed....... I just.... don't get any of this exposure stuff..... please, help me!!!!:lol:

[Jim_T]

Exposure compensation is just that.... A way of COMPENSATING when the camera's automatic exposure isn't doing what you want.

The AutoExposure in the EOS camera is good, but it's not PERFECT.. There are occasions when the metering gets fooled..

One example is when photograhing a small dark object against a bright sky.. The metering sees a lot of bright sky and meters for a very bright scene.. As a result, the small dark object turns out black.. Underexposed..

To compensate for this, you add compensation (+).. In Tv mode, it will widen the aperture and in Av mode it will lengthen the shutter speed.... There is no simple rule.. If adding one 'notch' of exposure compensation isn't enough, then add another..

Conversely, if you're shooting a bright white object against a very dark background, the camera will meter for all the dark and the white will be overexposed.. In this case you have to dial (-) compensation as required... (See another recent thread in this forum about an overexposed wedding dress)

The numbers are stops.. You can add or remove up to 2 stops of the exposure the camera's autoexposure chose...

[blue_max]

Just for another way of explaining it if it helps –
The camera expects to see an average scene and looks at most of the light hitting the sensor. If it is very bright, it will reduce the exposure and visa versa.

If your intended subject appears darker or lighter than the average of the general scene, then they will be wrongly exposed. The exposure compensation tells the camera that although it looks very light (or dark), don't worry about it. The scene will be wrongly exposed, but the subject will be fine.

You might expect that technology would be able to read your mind about what is of interest in the scene, but sadly only the photographer truly knows that. An alternative is to review your shots and spot the ones that the camera got wrong and be wary next time you shoot in a similar enviroment – or at least bracket the exposure.

Graham

[Steven M. Anthony]

Another situation where exposure compensation comes in handy is a snow-filled scene (like at a ski race or snowboard competition). Since the meter in the camera is aiming to rendure a neutral gray scene, it will underexpose the snow and leave it looking gray instead of white. Dialing in some compensation will help get the snow white again.

[RbrtPtikLeoSeny]

Thanks, that really helps. So, if I'm taking a picture of a flower or something, where the flower, and the background seem to be the same brightness, I should get the exposure at 0?

This is just so confusing for me. For example today I was shooting a picture of my brother inside, low light condition.... The camera wanted me to use f/1.8 ISO H and 1/30th second shutter speed to get a properly exposed picture without flash. So, I popped the flash up, manually set it to ISO 1600 f/5.6 and 1/250th shutter speed with the flash, and it came out fantastic! But during the shot the exposure was at -2 and blinking... so I'm like.....????????? Does it not factor in the flash or something?

[robertwgross]

Does it not factor in the flash or something?

Exactly.

When you shoot in one of the standard exposure modes, the camera does not know what the flash is going to make of it. It can know that the flash is present, but it doesn't know how things are going to be exposed. Then, you push the button, and the pre-flash pop happens at low intensity. That light reflects off the subject and comes back for metering. The meter makes a last second adjustment to shutter or aperture, and then the main flash pop happens.

---Bob Gross---

[robertwgross]

Exposure compensation is taught as a topic in just about every decent camera class. It works just about the same for film or digital, so everybody needs to learn it once.

---Bob Gross---

[Poco]

I would also add that if you don't get the exposure stuff you should probably stay away from the manual setting (M) for a while. Let the camera figure out the automatic adjustments based on either you setting the aperture (Av) or the shutter speed (Tv) and, if the result is too dark then set the exposure compensation higher, if it is too dark set it lower. Then learn by what the camera chooses. After a while you will understand what all the settings mean and be able to really take advantage of the manual settings.

I'm still learning myself and have not had a good reason to ever use the fully manual mode. The only case where I would (and I know other people have other reasons) is if I wanted to lock the settings across multiple photos like for a panoramic or something.

[tim]

Thanks, that really helps. So, if I'm taking a picture of a flower or something, where the flower, and the background seem to be the same brightness, I should get the exposure at 0?

This is just so confusing for me. For example today I was shooting a picture of my brother inside, low light condition.... The camera wanted me to use f/1.8 ISO H and 1/30th second shutter speed to get a properly exposed picture without flash. So, I popped the flash up, manually set it to ISO 1600 f/5.6 and 1/250th shutter speed with the flash, and it came out fantastic! But during the shot the exposure was at -2 and blinking... so I'm like.....????????? Does it not factor in the flash or something?

There are a bunch of concepts around this that you need to know, around how exposure works, how flashes work, how flash exposure compensation works, etc. I can't claim to be an expert, but I can get good photos in most circumstances now. btw the answer to your first question above is "no", and the answer to your second is "yes".

Now this is my view, and probably oversimplifies things, but it's a start. The camera makes the assumption that every scene is 18% grey - that is, it's closer to pure black than pure white. This turns out to be a reasonable assumption a lot of the time, but not always. For example, if you're on a snowy mountain taking a picture of your friend who's dressed in all black, them taking up 1/4 of the frame, the scene will be around 75% grey. To get the scene to be 18% grey, the camera doesn't open the shutter for as long, so the whites end up looking grey. Using exposure compensation you'd set EC to around +2, to tell it to assume the scene is two stops lighter than 17% grey - I can't do the calculations so i'll let someone more knowledgable do them, but the end effect is your snow will come out looking white.

You can try this out at home, by taking photos of objects in front of a white wall. Put something dark in the way, and take photos with just that object and the white wall in the background. Make the dark object take up maybe 10%, 25%, 50%, 75%, and 90% of the frame, and look at the histogram to see what happens.

Next is flash exposure. Actually i'm not even going to go into that right now, flash photography's even more complex and it's best to learn things one at a time.

Hope that helps rather than confuses, and if anyone can see flaws in what i've said please let me know and/or correct them.

[RbrtPtikLeoSeny]

Thanks! Yea, I should stay away from full manual for now. I just like to challenge myself...... anyway my camera came with a bunch of free photography classes I can attend on saturday mornings each week for a lil while. So, I'll definately go do that and hopefully I'll learn at least the basics of this stuff there.

This is a start though! Now I have a better idea of what the exposure compensation does. So, thank you all for that!

If anyone else has something to add. Please feel free to do so.

[Rokkorfan]

There are two different subjects that are being discussed here. One is normal exposure compensation (EC), and the other is Flash Exposure Compensation (FEC). I will deal with these seperately.

When taking an exposure the camera meters the scene and sets the exposure to obtain what it considers to be a correctly exposed shot. Most shots comprise a mixture of tones, and accordingly the camera is set to provide correct exposure for an arbitrarily decided average of these tones, called 18% gray. This is the same tone as a kodak gray card (which is designed for metering). Hence, if your subject is of average tonality it will be approximately 18% gray, and a good exposure will result.

However, let's say you are taking a photo of a white cup on a white table. The camera does not know what you are photographing, and hence it tries to get the exposure to be correct for a mid-toned (18% gray) scene. As a result it assumes that the light level is high, and it will reduce the exposure to achieve an 18% gray subject. This means your shot will turn out gray. Same goes if you are taking a photo of a black dog on a black rug. The camera assumes that it is a gray subject in low light, and will overexpose the subject. Your dog comes out gray, not black.

For these reasons you use the EC control to adjust exposure. You know that it is a white cup and a white cloth, so you add an extra 1.5 stops to the exposure, the camera then takes a shot correctly exposed. Same for the black dog, except you take off 1.5 stops. You can conduct this test yourself quite simply: In constant lighting conditions shoot a grey card, a black page and a white page. In each circumstance the camera will adjust the exposure to obtain a gray photo. Next shoot again and adjust the EC to achieve correct exposure - you will see that the shots now look correct. Experiment with the amount of EC required to achieve perfect exposure.

Note that this is only for shots that have a majority of light or dark tones - in most normal cases the camera will expose correctly.

FLASH EXPOSURE COMPENSATION

FEC in Canon bodies works similarly to normal exposure comp. The camera actually emits a pre-flash which is metered prior to exposure, and based upon the light reflected to it it will make an adjustment to the amount of light emitted by the main flash for correct exposure. Accordingly you can set your manual exposure anywhere (under the camera's sync speed) and the flash will emit the correct amount of light for a well exposed shot.

You use FEC primarily when you wish to adjust the amount of flash for aesthetic reasons. For example, let's say you are using fill flash in daylight. With no exposure compensation the camera will tell the flash to emit enough light to correctly expose the scene for flash. However, this will result in unnatural shots, as the flash becomes the principal light source. Accordingly in these circumstances you adjust your FEC down 1.5 stops to give a subtle fill to the face (again, experimentation is the key).

CANON FLASH MODES

When shooting in AV or TV with flash the camera will try to obtain enough light for a correctly lit ambient light photo, even when the flash is on. This can result in blurred shots, due to camera shake. Hence some photographers shoot flash in manual mode, setting the shutter speed and aperture to whatever suits them, in the knowledge that even though their ambient exposure may be low, the flash will simply emit enough light for a correct exposure. This gives them more control over the level of ambient light in the shot, and also means they can control the depth of field. Other photographers (particularly beginners or people with less time to mess about) will set the camera to P mode, where the shutter speed is restricted to a minimum of 1/60 second when using flash - hence reducing the risk of camera shake.

In these circumstances, when shooting a predominantly white subject the photographer must add FEC to get a correctly exposed shot.

TYPICAL ISSUE FOR BEGINNERS

Situation: You take a shot of people in the dark outside in P mode - the faces come out all overexposed.
Reason: The scene is darker than usual due to the night - the flash tries to light the background, and so emits a big burst which overexposes exeryone's face.
Solution 1: You recognise that the scene is darker than 18% gray, and so you set EC down 1 or 1.5 stops.
Solution 2: Using a tripod you set the camera to AV. The camera uses a long exposure to correctly expose the background, and a flash to correctly expose the people in the foreground. You must use FEC to reduce the light on peoples faces so they aren't washed out - say minus 1.5 stops.

Cheers,

Antony