What is really the use of ev?

[Prachin]

I guess its not that great question to ask..however i have been trying to knnow what does really EV helps in photography...i saw people writing Exposure Bias..+1,+2... but i couldnot get whats it use..where..when and what condition it is required to use..
i will be glad to know about its uses..thankyou
Prachin
Nikon D40
http://www.flickr.com/photos/34881236@N02/

[kirbinster]

I'll leave it to others to give you the detailed technical explanation - here is the simple one. Let's say the camera pickes an exposure for you in program mode that is 1/125th of a second at f 5.6, but when you take the picture you notice it is underexposed. You can bump the exposure compensation up to say +1.0 ev to correct for this. If it was over exposed you could go down on the exposure compensation. There are many reasons why the in-camera metering might get it wrong, but this give you an easy way to adjust to make the picture more pleasing to you. How is that for simple?

[dcclark]

Another simplified answer: "exposure" is really a one-dimensional measure: it tells you how much light could get onto the camera's sensor. This depends on your shutter speed, aperture, and ISO, but changing any one of these only allows in more or less light. (For example, double the shutter speed and move your aperture open by 1 stop -- you'll have the same amount of light coming in. We're ignoring questions like depth of field for the purposes of this...)

So, "EV" = "Exposure Value" measures how much light comes in to your camera. It abstracts away the ideas of shutter speed, aperture, etc. and just represents amount of light. So, there are many different camera settings which could produce the same EV: for example, ISO 100, shutter 1/100, and aperture f/2.0 would give the same EV as ISO 100, shutter 1/50, and aperture f/2.8.

So, the purpose of EV is to give a more absolute idea of how much light comes in to the camera, ignoring the details of the exact settings. Changing the EV in software means changing the photo to look like more or less light came in, usually by brightening or darkening.

[Doug Pardee]

You would use exposure compensation to make photos brighter or darker than the camera's Automatic Exposure system would normally choose to make them.

To be picky: Ev is the unit measure for exposure compensation. Kind of like seconds are the unit measure for your microwave timer. "Ev" stands for "Exposure value". It's about the only surviving legacy from the APEX system. More trivia: the Ev scale for exposure compensation is backward from the APEX usage of the term Ev.

[B..]

Originally Posted by Prachin

I guess its not that great question to ask..however i have been trying to knnow what does really EV helps in photography...i saw people writing Exposure Bias..+1,+2... but i couldnot get whats it use..where..when and what condition it is required to use..
i will be glad to know about its uses..thankyou
Prachin
Nikon D40
http://www.flickr.com/photos/34881236@N02/

Example 1: Taking a photo of snow or beach. The overall brightness of the image will be high, but your camera will try to make "bright" look like 18% gray. So you'll want to set to overexpose so that the snow or sand looks really bright.

Example 2: Taking a photo of something in a shadow. The overall brightness of the image will be low, but your camera will try to make "bright" look like 18% gray. So you'll want to set to underexpose so that the shadows will look really dark.

(If you use spot exposure metering, then the above doesn't necessarily apply ... just make sure your 'spot' includes only what you want to come out at around 18% gray.)

A third hint from a photo expedition I went on ... we were taking outdoor photos in the late afternoon. Our leader suggested that a tiny bit of underexposure would redden the photos and give them a bit more drama.

B

[kencaleno]

Here's a table showing Exposure values for each aperture/shutter speed combination:

Exposure Value zero (EV 0) corresponds to exposure time of 1 second and aperture of f/1.0 . EV 1 is either 1/2 seconds and f/1.0 or 1 second and f/1.4 , etc.

Other EV numbers can be found in the following table:


a p e r t u r e v a l u e
1.0 1.4 2.0 2.8 4.0 5.6 8.0 11 16 22 32 45 64
s 1 0 1 2 3 4 5 6 7 8 9 10 11 12
h 2 1 2 3 4 5 6 7 8 9 10 11 12 13
u 4 2 3 4 5 6 7 8 9 10 11 12 13 14
t 8 3 4 5 6 7 8 9 10 11 12 13 14 15
t 15 4 5 6 7 8 9 10 11 12 13 14 15 16
e 30 5 6 7 8 9 10 11 12 13 14 15 16 17
r 60 6 7 8 9 10 11 12 13 14 15 16 17 18
125 7 8 9 10 11 12 13 14 15 16 17 18 19
s 250 8 9 10 11 12 13 14 15 16 17 18 19 20
p 500 9 10 11 12 13 14 15 16 17 18 19 20 21
e 1000 10 11 12 13 14 15 16 17 18 19 20 21 22
e 2000 11 12 13 14 15 16 17 18 19 20 21 22 23
d 4000 12 13 14 15 16 17 18 19 20 21 22 23 24

[RoyL]

EV comes into play when the camera can be fooled, ei, predominantly white (like snow) or dark area's. The camera will come up with an incorrect exposure reading because it see's everything as 18% grey, so if you are shooting a snow scene you may have to adjust by -2 Stops to get white snow, or +2 to get true dark color. Sort of. If you did not do this then you would end up with underexposed (snow) or overexposed (dark area) images.

Then you can also make adjustments for creative work. And then everything that everyone else has said.