How exactly does EV compensation work

[kirbinster]

I know that ev compensation adjusts for how the camera meters a shot so that you can increase or decrease the exposure, but what exactly does it do. Let's say I have the camera set to manual mode and set it at 1/125th of a second af f/8 and ISO 200, if I dial in +1.0 ev or -1.0 ev what exactly is being adjusted to change the exposure?

[wulf]

How do you dial it in when you are in manual mode? On my D40, a metering lens will show the effects of my adjustments and whether the camera thinks the image is properly exposed or not but I can't be in manual AND have the camera take control of exposure.

Wulf

[SusanH1970]

In a nutshell, it underexposes or overexposes a photo. For instance, if you're photographing a snow scene, it's usually a good idea to overexpose it a bit. The human eye sees the snow as white, but the camera sees it as grey. Over exposing will make the snow look white in the photo.

Underexposing is good if you're shooting something with a lot of dark colors or black, for example, a group of guys in a wedding, wearing black tuxedos, near a black limo.

I'm sure someone with more experience with this can add a lot more info.

[jprime84]

I dont think it is changing the physical properties of the light traveling to the sensor if thats what you mean. Not sure exactly though

[BryanC]

It depends on the particular camera, but generally, in auto it adjusts the aperture or shutter speed, or both. If shooting in aperture priority, it will adjust the shutter speed. If in shutter priority, it will adjust the aperature. In full manual, you can't use the EV comp, since both aperature and shutter are controlled manually.

[kirbinster]

Thanks Susan, I understand all that --- what I am asking is the actually mechanics of how the ev comp works.

Wulf - don't recall about the D40 as I gave mine to my dad, but on my D80 and D300 I can go to manual mode and dial in a set shutter speed and f-stop and then also press the ev button and dial in an exposure comp value from +5.0 down to -5.0. My question is what (if anything) does this actually do when in manual mode?

[SusanH1970]

Oh, okay, now I see what you're asking. I'm sure you already know about what I previously posted. I was unclear on what you were asking till I read the other replies. So just ignore what I said.

[vandergus]

Well, if you're in manual mode, it won't change the actual exposure at all (unless you have auto-iso on). It will just change the reading that the meter shows in the viewfinder.

[WenRob]

I'm by no means an expert but I use the EV in manual on my D90 all the time. Usually indoors I up it to +.03-+.07. It brightens my exposure just that little bit without affecting my Aperture or Shutter Speed. When it's super bright inside I lower it so I don't get hot spots on cheeks and foreheads. Again in manual and it doesn't affect what I've dialed in. Exactly how it works, I have zero idea but I use it quite a bit for inside shots, especially if I don't want widen my aperture. Hope this makes sense and I don't sound like a complete idiot.

[Jim Bryant]

Most all digital cameras have an Exposure Value (EV) Compensation setting. This setting is needed because the camera can sometimes make incorrect assumptions about the lighting of a photo. Changing the EV will make sure your photos are always correctly exposed.

Why Do We Need Exposure Value Compensation?

Your camera is calibrated to expose images correctly for scenes that have a mix of dark and light areas. This works well in most situations because our images normally tend to have brighter areas (sky) and darker areas (shadows). On Auto, the camera chooses a brightness setting around mid way between the brightest and darkest areas and makes sure that area is correctly exposed.

This causes problems, however, when all of your image is very bright (like a white sandy beach or snow), or very dark (like deep green forest scenes). For very bright scenes, like at the snow, the camera thinks the very bright part should be the ‘mid point’. This causes the snow to appear gray (because it’s mid way between white and black). Similarly for darker images.

The snow in this image looks grey because there is too much ‘white’ in the image. This fools the camera’s settings

How To Use EV Compensation

EV Compensation helps to fix this by telling the camera to expose at a higher or lower setting than it thinks is right. For very bright settings (like the snow or beach), set an EV value as a positive number (+1/3, +1 etc). For very dark scenes, choose a negative EV number.

Now, I know what you’re thinking - that doesn’t make sense! If the subject is very bright, don’t I need to set a lower EV (negative number) to make sure the image is exposed correctly?

Well, no. It’s the opposite. It helps to think of what the resulting image will look like. In the snow, where there are lots of bright areas, the camera will choose a mid point in the bright area, so the snow will look gray in the resulting image. To fix that and make the snow white (as it should be), we need to brighten the image. Thus we need to increase the exposure and use a positive number.

The same with very dark subjects. The camera will choose a very dark point as the mid-point so everything will appear too bright in the image. We need to lower the exposure (negative number) to compensate.

Setting the EV to +1 fixes the gray snow. It’s now bright white.
Thanks to forum member snowfall1127 for the use of this image.

Exposure Bracketing

Even if you know the direction (+ or -) to set the EV, it’s harder to judge how much to compensate. My suggestion is to try different values and check using the LCD screen after each until your photo looks right (not too many very light or dark points).

Some cameras can even do this automatically (Called Auto Exposure Bracketing). I don’t recommend using this as YOU will be a much better judge of a correctly exposed image than your camera.

EV –2, EV –1, EV 0
Normal Exposur
EV +1, EV +2
Use Your Camera’s Scene Modes

If you don’t want to worry about exposure value, check to see if your camera has scene modes. The Beach and Snow scene mode automatically sets the appropriate EV compensation so these images won’t appear too dark.

For Sunset/Sunrise
Surprisingly, changing EV is a great way to capture stunning sunsets. The sun tends to mess with the exposure as it’s a very very bright spot (even at sunset). The camera tries to compensate and sets a higher exposure. This darkens the rest of the image and destroys any of the colors in the sky.

To get the colors back, set the EV to +1 or +2. This will increase the exposure which will lighten the rest of the image, and bring the colors back!
Summary

Use Exposure Value Compensation when your scene is all very bright, or all very dark. Use positive numbers for bright scenes and negative numbers for dark scenes. Experiment with different numbers until your image is correctly exposed.