Exposure Compensation - question

[PhillyPhoton]

Hello everyone,
So tonight Im trying to understand what exposure compensation does, so far all Ive adjusted is the ISO/AP/SP.
2 questions:

1) can anyone give me an example of when they have used exposure compensation ( I do know that it will adjust flash output so I can see it usefull there) but the manuel is confusing as to what it actually does when there is no flash

2) if its not affecting the ISO/AP/or SP how is it affecting the exposure, if other than the flash?


sorry about the newb question

 

[Overread]

Ok don't confuse yourself with flash just yet - focus on shots purely with the three key settings of Aperture, shutter speed and ISO. In a DSLR these are the only 3 settings that it has to control the exposure.

When you take a shot in aperture or shutter priority the camera controls one settings whilst you control the other two - the camera lets you choose those two settings and then meters the scene before selecting its setting value based on the meters reading of that scene. However the camera's meter can get fooled or you might want to do something creative away from the "ideal" exposure. An example is shooing in the snow, where the bright snow often comes up dull grey when the camera meters because its trying to make verything 18% grey in colour - so you'd use exposure compensation to tell the camera to overexpose the shot (thus set its one controlled setting to overexpose).
Another example is in strong sunlight where a little underexposure will help to try and keep highlights from blowing out.

When it comes to flash exposure its the same again; only this time you're telling the flash to under/overexpose its light output based on its meter reading of the scene and the settings you have set in the camera.

 

[PASM]

I try it when the camera is attempting to meter the scene but the histograms show clipping of data.

 

[PhillyPhoton]

Ok don't confuse yourself with flash just yet - focus on shots purely with the three key settings of Aperture, shutter speed and ISO. In a DSLR these are the only 3 settings that it has to control the exposure.

When you take a shot in aperture or shutter priority the camera controls one settings whilst you control the other two - the camera lets you choose those two settings and then meters the scene before selecting its setting value based on the meters reading of that scene. However the camera's meter can get fooled or you might want to do something creative away from the "ideal" exposure. An example is shooing in the snow, where the bright snow often comes up dull grey when the camera meters because its trying to make verything 18% grey in colour - so you'd use exposure compensation to tell the camera to overexpose the shot (thus set its one controlled setting to overexpose).

Another example is in strong sunlight where a little underexposure will help to try and keep highlights from blowing out.

When it comes to flash exposure its the same again; only this time you're telling the flash to under/overexpose its light output based on its meter reading of the scene and the settings you have set in the camera.

Ok, so say Im in aperture priority, and I want to decrease the exposure, when I decrease its just going to override the shutter speed (what the camera is controlling) and make it faster..is that correct?

 

[Overread]

Yes exactly; the camera will read the light - then take into account the exposure compensation and compensate its set value to meet that value. As in your example it would push the shutter speed faster, remembering of course that it will be underexposing the shot from the meters read value.

You would get the same as if you went into manual mode and balanced the settings with the meter needle pointing off the middle of the line (ie toward underexposure in this case)

 

[PhillyPhoton]

Thanks Overread,
Now that I understand that I really cant see me using it, in manuel mode as you say you can see the exposure meter and the shutter and aperature controls are right at your finger. I'll have to see if this comes in use. I think I'll end up using the flash compensation until I get the sb600.
thanks again
there's two more buttons I can check off the list :mrgreen:

 

[Edsport]

When taking pics of snow the camera sees it as being bright and will usually underexpose the image even though the camera is set to take a normal exposure. When taking photos of snow it's a good idea to set the camera to compensate by telling it to overexpose by +1 or so. This is just an example of when to use exposure compensation...

 

[PhillyPhoton]

When taking pics of snow the camera sees it as being bright and will usually underexpose the image even though the camera is set to take a normal exposure. When taking photos of snow it's a good idea to set the camera to compensate by telling it to overexpose by +1 or so. This is just an example of when to use exposure compensation...

thanks Edsport, Overread had mentioned that as well, going to keep that in mind.

 

[Phranquey]

When I'm doing bird shots, if I have one up in a tree with a bright background, it will come out as a silhouette under normal metering. Bump EC anywhere from +1 to +3, depending on the brightness, and it will overexpose the background while giving me a well exposed bird & branch.

 

[thatfornoobs]

If you were in say a bright room, you may turn the exposure compensation down, by using a lower ISO number, or faster/longer shutter speed in order to "compensate the exposure"!

 

[Garbz]

One thing to keep in mind is that the camera will only modify the aspect that is not fixed by you. Going through the modes:

P : Anyone's guess
A : Aperture and ISO fixed, shutterspeed is automatic.
S : Shutter speed and ISO fixed, aperture is automatic.
M - With auto ISO: Shutter speed and Aperture are fixed, ISO is automatic.
M : Everything is fixed. The camera will only automatically compensate it's internal light meter that you see through the viewfinder. So it will read how much you're over / under exposing based on the compensated value. But the picture won't change unless you change some setting yourself.

Overread's comment was also incredibly over simplified. The modern camera no longer exposes for 18% grey. In reality it uses a complex sensor and fancy algorithms to determine the exposure, or even in simple modes it will centre weight the reading or spot meter based on a focus point or something like that. But the underlying concern is that ultimately it's still just guessing, and exposure compensation allows it to continue guessing yet gives us control to bias it one way or the other.

 

[ann]

Recently I called Nikon to get the answer to this question "what value is changed with exposure compensation" i.e. fstop 4 shutter speed 125, what changes? After getting someone else on the phone (not the usual question for tech support) I was told neither but the change is made internally within the chip.

 

[Big Mike]

Thanks Overread,
Now that I understand that I really cant see me using it, in manuel mode as you say you can see the exposure meter and the shutter and aperature controls are right at your finger. I'll have to see if this comes in use. I think I'll end up using the flash compensation until I get the sb600.
thanks again
there's two more buttons I can check off the list :mrgreen:

Yes, if you shoot in manual mode (and know what you're doing), you don't need EC because you probably aren't adjusting the settings to get the 'needle' to the --0--.

Canon agrees, and that is why there is no EC when in manual mode. The button/dial that controls EC (in auto modes) just controls aperture when in manual mode.

Nikon, on the other hand, does allow the EC to be set while in manual mode...and in that situation, all it's really doing, is offsetting where your meter needle shows up.
For example, if you were shooting with a lot of snow in the scene, you would probably want to overexpose from the meter's suggested exposure value. Lets's say you wanted to shoot at +1. You could just adjust your settings until the needle was at +1, or you could dial in +1 EC, then adjust the settings to get the needle to --0--.
Seems silly to me...but that's Nikon for you

Recently I called Nikon to get the answer to this question "what value is changed with exposure compensation" i.e. fstop 4 shutter speed 125, what changes? After getting someone else on the phone (not the usual question for tech support) I was told neither but the change is made internally within the chip.

As per my explanation above, in manual mode (on a Nikon), EC doesn't actually change either of the exposure settings...but it does change the meter reading (where the needle falls). And then it's up to the user to choose which settings they want to alter, to get the needle back where they want it.
So I guess what they're saying, does make sense.

 

[ann]

I know that in manual mode it isn't needed, and it is just recently that Nikon will allow EC to work in all modes.

This question was asked in my beginner class and they are using aperture and shutter priority modes, not manual.

 

[Big Mike]

This question was asked in my beginner class and they are using aperture and shutter priority modes, not manual.

Well in A, it should change the shutter speed and in S, it should change the aperture. Doesn't it work that way?

In my DSLR class, one of the Nikon using students couldn't figure out why here settings were so different from the student next to her (taking shots in class, manual mode). Turns out that her EC was set to -3 or something like that.