What exactly is EV compensation & what (physical attribute) is it adjusting?

[ralliart12]

Hi fellows. Got a qn that has been puzzling me for a while now. I understand the effects of adjusting the following 3 attributes of a shot:

1. Aperture: adjusting the size of the aperture hole to constrain how much light enters the aperture at a single moment

2. Shutter speed: adjusting how long the shutter stays open, again to constrain the net amount of light that is captured/absorbed during a shot

3. ISO: adjusting how sensitive the sensor of the camera is, to the amount of light that it receives, at the expense of noise.

What I don't understand, is this "ev compensation" found on most cameras, that allows increments in both directions of 1/3 stops graduations. However, what is it really tweaking? I know it makes the final result brighter/darker, but is it achieving this by overriding any of the 3 attributes mentioned earlier, & if not, how does it make the photo brighter or darker without using those 3 attributes?

Thanx in advance.

 

[cmeptb72]

Depends on which camera shooting mode you're using...

Normally,

1) If you're using AV mode, the aperture setting is fixed whilst the shutter speed is affected

2) If you're using TV mode, the shutter speed is fixed whilst the aperture is affected

If you're setting the ISO manually, ISO setting shouldn't be affected by EV+/- compensation.

Cheers

 

[ralliart12]

Depends on which camera shooting mode you're using...

Normally,

1) If you're using AV mode, the aperture setting is fixed whilst the shutter speed is affected

2) If you're using TV mode, the shutter speed is fixed whilst the aperture is affected

If you're setting the ISO manually, ISO setting shouldn't be affected by EV+/- compensation.

Cheers

Hi, does your "...is affected" = "override" by EV compensation?

 

[Dream Merchant]

Think of EV as an absolute value.

Aperture and shutter speeds as variables.

ANY combination of aperture or shutter speed can be adjusted to obtain a certain exposure relative to an EV value/reading.

An 'automated' EV adjustment affects a camera's settings as cmeptb72 described.

 

[ziploc]

And to add to what cmeptb72 had mentioned:

3) If you're using P mode, either the shutter speed or the aperture or both are affected, and the camera will determine that.
4) If you're using M mode, none is affected - it will only affect the light meter displayed in your viewfinder.

To give you an example:
If you're shooting in aperture priority mode, and the exposure is at f/5.6 1/500s. If you dial in an EV compensation of +1 EV, the exposure set by the camera will now become f/5.6 1/250s (since aperture value is fixed, the camera will change the shutter speed).

 

[ziploc]

Hi, does your "...is affected" = "override" by EV compensation?

Not exactly "override", although you can call it that way. What happen is that the camera will add the EV compensation value to the metered value to get the final setting. So in my example above, original exposure metered by the camera is f/5.6 1/500s. After adding +1 EV (+1 stop) to the shutter speed, the resulting value becomes f/5.6 1/250s (1/500s -> 1/250s is +1 stop).

 

[ZerocoolAstra]

Actually, TS, if you had aimed your camera at a fixed spot and taken 2 consecutive shots with and without any EV compensation, and then analyzing the EXIF info on aperture, shutter speed, ISO speed, you would have arrived at the answer which ziploc has kindly explained to you.

 

[ralliart12]

And to add to what cmeptb72 had mentioned:

3) If you're using P mode, either the shutter speed or the aperture or both are affected, and the camera will determine that.
4) If you're using M mode, none is affected - it will only affect the light meter displayed in your viewfinder...

Really appreciate the additional information regarding the compensation behaviour in non-priority modes.

...To give you an example:
If you're shooting in aperture priority mode, and the exposure is at f/5.6 1/500s. If you dial in an EV compensation of +1 EV, the exposure set by the camera will now become f/5.6 1/250s (since aperture value is fixed, the camera will change the shutter speed).

This example is very clear. Thank you. Exactly what I'm looking for.

Not exactly "override", although you can call it that way. What happen is that the camera will add the EV compensation value to the metered value to get the final setting. So in my example above, original exposure metered by the camera is f/5.6 1/500s. After adding +1 EV (+1 stop) to the shutter speed, the resulting value becomes f/5.6 1/250s (1/500s -> 1/250s is +1 stop).

So, in the end, can I say the main idea for EV compensation is to adjust the brightness after the photographer has tweak aperture/shutter speed/ISO to achieve the effect he wants, i.e. after tweaking shutter speed to freeze action, or tweaking aperture to get bokeh, & I still wanna adjust the brightness, then I go do EV compensation?

Actually, TS, if you had aimed your camera at a fixed spot and taken 2 consecutive shots with and without any EV compensation, and then analyzing the EXIF info on aperture, shutter speed, ISO speed, you would have arrived at the answer which ziploc has kindly explained to you.

Got it; my bad. I didn't try this because I thought I wouldn't know what to look out for.

Lastly, any side-effects of EV compensation? I know ISO will affect noise levels, but if EV compensation has no down-side I suppose everyone will tweak it instead of ISO to achieve desired brightness?

 

[shahrulesa]

Well, you use EV for various reasons
- if your picture is too dark, than +EV to make it brighter
- Also, if you're shooting a dark subject (man in suits maybe), than reduce EV to make the black 'blacker'
- If you're shooting white dress perhaps, then increase EV to make the dress 'whiter'
- you can also use EV bracketing to do HDRs

 

[ziploc]

So, in the end, can I say the main idea for EV compensation is to adjust the brightness after the photographer has tweak aperture/shutter speed/ISO to achieve the effect he wants, i.e. after tweaking shutter speed to freeze action, or tweaking aperture to get bokeh, & I still wanna adjust the brightness, then I go do EV compensation?

Lastly, any side-effects of EV compensation? I know ISO will affect noise levels, but if EV compensation has no down-side I suppose everyone will tweak it instead of ISO to achieve desired brightness?

The main purpose of the EV compensation is to, as the name implies, compensate for the exposure metered by the camera. This is needed because, e.g. in spot metering mode, the camera is metering for 18% (mid) gray. If you spot meter e.g. snow, the camera will try to make the snow mid tone, and so the snow will end up mid gray instead of white. In order to compensate for this problem, you can dial in +1.5EV~+2EV to compensate for the exposure to make the snow white.

There is a handout I wrote quite some time ago when I conducted introductory photography courses for newbies. Perhaps you would like to take a look for more detailed explanations:

http://www.clubsnap.com/display.php?file=articles/photography101/photography101.html

Are there down-sides for EV compensation? Yes. For example, if you're shooting with a 200mm lens in A mode with the shutter speed at 1/250s. If you now dial in +1EV compensation, the shutter speed now drops to 1/125s which might be too slow to hand held the 200mm lens. And for the ISO example you mentioned, there is no such thing as a "free lunch". When the available light is limited, you only have 3 parameters to play with - aperture, shutter speed, ISO. If you do not want to increase the ISO, you will have to either open up the aperture or lower the shutter speed, which EV compensation is doing exactly. If the aperture is already at the widest or the shutter speed is at an unacceptably low level, you have no choice but to increase the ISO.

Hope that helps.

 

[Gangru]

I have always thought that EV compensation is way to manipulate your light meter to read the scene the way you want it.

Because the DSLR light meters read light based on middle grey, you can tell the meter to read the scene lesser than middle grey or above middle grey values.

For example : If you are shooting a sunset where you want your silhouettes to be blacker, you dial in a negative compensation, so as to fool the camera to read below middle grey..

Am I correct? Just to get my understanding clear.

 

[ziploc]

I have always thought that EV compensation is way to manipulate your light meter to read the scene the way you want it.

Because the DSLR light meters read light based on middle grey, you can tell the meter to read the scene lesser than middle grey or above middle grey values.

For example : If you are shooting a sunset where you want your silhouettes to be blacker, you dial in a negative compensation, so as to fool the camera to read below middle grey..

Am I correct? Just to get my understanding clear.

Yes that is correct, although I won't call it "fooling the camera".

 

[ZerocoolAstra]

I have always thought that EV compensation is way to manipulate your light meter to read the scene the way you want it.

Because the DSLR light meters read light based on middle grey, you can tell the meter to read the scene lesser than middle grey or above middle grey values.

For example : If you are shooting a sunset where you want your silhouettes to be blacker, you dial in a negative compensation, so as to fool the camera to read below middle grey..

Am I correct? Just to get my understanding clear.

It's not really fooling the camera, but rather, over-riding the pre-defined settings because the situation at hand is not... how do I say... a "default" kind of scene.

 

[FrancisGabriel]

Do we adjust the ev compensation when using a flash?

 

[ZerocoolAstra]

You can... but once again, it depends on what mode you're using.