Exposure and Exposure Compensation?

[dmw16]

I have a question regarding the use of exposure compensation.

I have been doing some reading and I think I have reached a basic understanding of exposure. I understand why a snow or beach scene will typically be underexposed and why a black cat on a pile of coal will typically be overexposed.

However, what confuses me a little is exposure compensation (and it's probably a dumb question). Is the purpose of exposure compensation only to change how the light meter in the camera reads the scene? Or does it actually directly impact the photo being taken?

 

[PurdueRy]

I don't quite get what you mean by "directly impact the photo being taken" vs. the way the camera meters a scene as they are directly correlated. The camera tries to evenly expose the area metered. If you do spot metering on a black cat in front of a white background you will end up with a much brighter picture if you spot meter on the cat rather than do a evaluative measurement over the entire scene.

Exposure compensation adjusts the final result of the metering. So if you know your camera read a dark scene and is going to or did overexpose it, you can set your exposure compensation to -1 to reduce the exposure by 1/2. However, if you adjust this and then meter differently, your picture may not come out with 1 stop exposure compensation.

 

[dmw16]

Let's say I have a scene (let's say a snow scene) and the camera is telling me that at f/2.8 @ 1/50 that my shot will be properly exposed. However, knowing that typically snow scenes will underexpose without compensation, I adjust my Exposure Compensation to (let's say) +.7.

Will adding that +.7 actually change anything about how the camera captures the scene (assuming I don't change my f-stop or shutter speed)? Or does it just cause my meter to display that my scene is going to be underexposed so that I know to adjust my f-stop or shutter speed?

 

[corkyg]

Originally posted by: dmw16
... Will adding that +.7 actually change anything about how the camera captures the scene (assuming I don't change my f-stop or shutter speed)? ...

Yes. What you are doing is, in effect, recalibrating the system light meter. A setting of +.7 will change all your pictures to that degree until you recalibrate again.

 

[PurdueRy]

Originally posted by: dmw16
Let's say I have a scene (let's say a snow scene) and the camera is telling me that at f/2.8 @ 1/50 that my shot will be properly exposed. However, knowing that typically snow scenes will underexpose without compensation, I adjust my Exposure Compensation to (let's say) +.7.

Will adding that +.7 actually change anything about how the camera captures the scene (assuming I don't change my f-stop or shutter speed)? Or does it just cause my meter to display that my scene is going to be underexposed so that I know to adjust my f-stop or shutter speed?

That will cause your camera to change the shutter speed or aperture to compensate for the change you made. If you are in Av mode it will change the shutter speed, if you are in T mode it will change the aperture.

 

[extra]

Originally posted by: dmw16
Let's say I have a scene (let's say a snow scene) and the camera is telling me that at f/2.8 @ 1/50 that my shot will be properly exposed. However, knowing that typically snow scenes will underexpose without compensation, I adjust my Exposure Compensation to (let's say) +.7.

Will adding that +.7 actually change anything about how the camera captures the scene (assuming I don't change my f-stop or shutter speed)? Or does it just cause my meter to display that my scene is going to be underexposed so that I know to adjust my f-stop or shutter speed?

Adding exposure compensation doesn't change how your camera pictures the scene at all... it just changes the actual exposure you are giving the film or sensor.

So, for example:

You dial in that +.7 EC. The camera WILL lower the f-stop or lower the shutter speed. That is how it changes the exposure. It's basically a way to have some manual over-ride in the automatic modes. Exposure compensation in manual mode is basically meaningless as you are adjusting it anyway.

 

[twistedlogic]

Originally posted by: dmw16
Let's say I have a scene (let's say a snow scene) and the camera is telling me that at f/2.8 @ 1/50 that my shot will be properly exposed.

(assuming I don't change my f-stop or shutter speed)

As others have stated, exposure compensation will only take effect of your exposure settings in automatic modes (Program, Aperture, Shutter priority). In manual mode, you control exposure but the meter is still reading, giving you a an idea of how the camera would have metered it. Applying EV in manual mode will effect how the meter shows to you but will have no impact on your chosen exposure settings or your final image.

So in your example, the camera meters f/2.8, 1/50ss, buy dialing in the exposure compensation to +1 (1 stop) your shutter speed will double(or aperture will open up, depending on camera mode), letting in more light to get the exposure you prefer.

 

[dmw16]

Thanks for the info. I should have mentioned this was assuming I was in manual mode. Makes perfect sense now, thanks.

 

[PurdueRy]

Originally posted by: twistedlogic

Originally posted by: dmw16
Let's say I have a scene (let's say a snow scene) and the camera is telling me that at f/2.8 @ 1/50 that my shot will be properly exposed.

(assuming I don't change my f-stop or shutter speed)

As others have stated, exposure compensation will only take effect of your exposure settings in automatic modes (Program, Aperture, Shutter priority). In manual mode, you control exposure but the meter is still reading, giving you a an idea of how the camera would have metered it. Applying EV in manual mode will effect how the meter shows to you but will have no impact on your chosen exposure settings or your final image.

So in your example, the camera meters f/2.8, 1/50ss, buy dialing in the exposure compensation to +1 (1 stop) your shutter speed will double(or aperture will open up, depending on camera mode), letting in more light to get the exposure you prefer.

On my camera(50D) I believe that I can't even mess with exposure compensation in manual mode as it does not want to adjust the settings that the user has already given. Makes sense, I like your analogy that it's just a way of overriding a semi-auto mode.

 

[magomago]

Originally posted by: PurdueRy

Originally posted by: twistedlogic

Originally posted by: dmw16
Let's say I have a scene (let's say a snow scene) and the camera is telling me that at f/2.8 @ 1/50 that my shot will be properly exposed.

(assuming I don't change my f-stop or shutter speed)

As others have stated, exposure compensation will only take effect of your exposure settings in automatic modes (Program, Aperture, Shutter priority). In manual mode, you control exposure but the meter is still reading, giving you a an idea of how the camera would have metered it. Applying EV in manual mode will effect how the meter shows to you but will have no impact on your chosen exposure settings or your final image.

So in your example, the camera meters f/2.8, 1/50ss, buy dialing in the exposure compensation to +1 (1 stop) your shutter speed will double(or aperture will open up, depending on camera mode), letting in more light to get the exposure you prefer.

On my camera(50D) I believe that I can't even mess with exposure compensation in manual mode as it does not want to adjust the settings that the user has already given. Makes sense, I like your analogy that it's just a way of overriding a semi-auto mode.

*
I'm going to describe things as I've understood it. If I made a mistake, someone explain it to me, but I'm pretty sure that EC doesn't affect the meter. To me, I'm defining the meter as the part of the camera that reads the light to determine exposure.*

I can't understand how one would apply exposure compensation in manual mode at all. It isn't about over riding any user settings. What is it going to change? It can't change anything lol. Its manual mode. You define Aperture and Shutter Speed.
When I'm in manual, I just get meter read outs from my cam. So if I'm in manual and I'm shooting a nice snowy area, I know if I'm doing it right if my meter reads +1EV

As for the EC - think of it as a linear correction applied to the settings the meter reports that the CAMERA uses. The meter itself won't change or adjust what it read. For a given ISO, if the meter thinks that (lets use Av for example, although any other mode like Tv, TAv, Sv also apply) at f/4 it wants to use 1/60, it will think that no matter how much EC you apply.
The meter has its own read out independent of EC that is applied. It reports to the camera was it thinks the settings should be; but now, because you told the camera to overexpose (to be more precise - the camera thinks it is an over exposure because it has documents from the meter that tell it what the scene should be, but you know better than that), and it will adjust the information fed to it by the meter and this will determine the final settings that the picture is taken at - no changes to the meter will occur. Doing +1EV will cause the camera to take the meter readout and increase the shutter speed to 1/30.
That is how I understand it from a logic standpoint, and I can't see how applying EC actually changes how the metering is read. It only changes the final settings that are used to take the picture.

Let us explain a scenario:

Given:
- A setting with a huge black rock that covers a quarter of the frame
- Av mode with f/8 selected
- A Pentax

Players:
- Meter --> He reads the light to determine the exposure based on the method is he told to meter by (Spot, Center Averaged, Matrix)
- Smart User who knows how to apply EC --> this is you!
- Camera --> He reviews all the information given to him before you see the displayed selection in the viewfinder.

Start of Theatrical Preformance

Meter "I'm reading this scene....Fuck this shit, its hella dark. He also reported a forced aperture of f/8. Okay, looking at the light I think this should should have a 1/15 shutter speed.!"

*Meters hands his final assessment to the camera and the camera reads the report to find out that the selected settings is f/8 @ 1/15th.*

Camera says "Okay, this is what we are given boys, now lets hold on for final review!"

*the user, at the last second, realizes that big black object is MEANT to be black....so we need some negative compensation. Faster shutter so black appears as black.*

*the user dials in -2EV and says, "Oh my, I love Pentax!"*


Camera says, "Hold on boys, the big boss said we need to under expose by a stop! Why? Don't question him - he has a brain and you have nothing!"

Camera says, "Okay, we can't change our aperture, so lets adjust that shutter. F/8 @ 1/60th. Hey display Unit, update it to the settings I just reviewed. Alright boys we are good to go. Let us rock this shit! ATOT FTW"

Notice how in the discussion above the meter wasn't involved.

 

[PurdueRy]

magomago, that is correct. Pretty sure no one disagrees with what you are saying. Just stating that the 50D doesn't let you adjust EC in manual mode. The only way it could adjust the exposure without changing the Aperture or shutter speed would be to adjust ISO but it considers that a user setting as well and doesn't want to mess with it. So you could do the same thing as EC manually, its just not as fast to change typically.

 

[magomago]

Originally posted by: PurdueRy
magomago, that is correct. Pretty sure no one disagrees with what you are saying. Just stating that the 50D doesn't let you adjust EC in manual mode. The only way it could adjust the exposure without changing the Aperture or shutter speed would be to adjust ISO but it considers that a user setting as well and doesn't want to mess with it. So you could do the same thing as EC manually, its just not as fast to change typically.

Lol I still think we have a disconnect...but I have this feeling that it might come down to terminology and or technicality.
How can you diasble 'adjusting' EC in manual? It doesn't exist in manual. It isn't like its disabled or something...it just conceptually doesn't exist in manual.
If you want to apply exposure compensation, you have to compensate for something else. That is why EC only makes sense within a predetermined exposure read from the meter, because you are compensating for the meter. Once you go to Manual, you control it all...do you compensate for your self lol? Its called adjust the settings yourself.
The only thing you can get is meter read outs to see what the meter thinks --> but nothing will ever affect the actual settings you chose.

Btw I didn't mean to quote you specifically lol. It almost sounded like it sounded that in one of the semi-auto modes, it was being suggested that that EC actually caused the meter to re-determine the scene.

Again I may be totally missing things since I'm at work so excuse me if I'm just not understanding your point

 

[PurdueRy]

Originally posted by: magomago

Originally posted by: PurdueRy
magomago, that is correct. Pretty sure no one disagrees with what you are saying. Just stating that the 50D doesn't let you adjust EC in manual mode. The only way it could adjust the exposure without changing the Aperture or shutter speed would be to adjust ISO but it considers that a user setting as well and doesn't want to mess with it. So you could do the same thing as EC manually, its just not as fast to change typically.

Lol I still think we have a disconnect...but I have this feeling that it might come down to terminology and or technicality.
How can you diasble 'adjusting' EC in manual? It doesn't exist in manual. It isn't like its disabled or something...it just conceptually doesn't exist in manual.
If you want to apply exposure compensation, you have to compensate for something else. That is why EC only makes sense within a predetermined exposure read from the meter, because you are compensating for the meter. Once you go to Manual, you control it all...do you compensate for your self lol? Its called adjust the settings yourself.
The only thing you can get is meter read outs to see what the meter thinks --> but nothing will ever affect the actual settings you chose.

Btw I didn't mean to quote you specifically lol. It almost sounded like it sounded that in one of the semi-auto modes, it was being suggested that that EC actually caused the meter to re-determine the scene.

Again I may be totally missing things since I'm at work so excuse me if I'm just not understanding your point

I didn't say it was "disabled". Actually the way it behaves on my 50D is you can try to adjust it as you normally would and it moves a bit and swings right back for obvious reasons.

Trust me, I know why there is no exposure compensation in manual. I'm simply trying to explain to the OP why that is.

 

[Shimmishim]

If you understand exposure then you'd understand that it is a combination of ISO, shutter speed, and aperture.

Shooting in manual, you'd set your ISO, SS, and aperture.

The camera meters the scene based on these settings plus the metering mode (spot, evaluative, center, etc...).

As you stated the camera gets confused when you meter for a snowy scene or a dark scene because cameras try to make everything (black or white) into 18% grey.

EC doesn't exist in manual as somoene stated because you have full control over everything.

In Av mode, you set the aperture and the ISO but don't have control over the shutter speed. In order to change the shutter speed you have to use the exposure compensation function to manually adjust the shutter speed slower or faster.

In Tv mode, you set the shutter speed and the ISO but don't have control over the aperture. in order to change the aperture you have to use the exposure compensation function to manually adjust the aperture bigger or smaller.

This is how I've always understood it.

 

[twistedlogic]

*all references are to Nikon DSL-R, not sure how other manufactures implement EC

EC can have effect in manual mode. I don't understand what you guys mean by it "does not exist" in manual mode.

Will it change your SS or Aperture for you? No. But it will effect how your light meter appears to you, it will effect your ISO if auto-ISO is left on, and it will effect your flash TTL metering.

"If exposure compensation is set when using automatic SLRs (F5, F100, N80, D100, D2H, etc.) in the manual exposure mode, the actual aperture and shutter speed settings do not change as they do if one of the automatic exposure modes is selected. Instead, the metering scale in the camera's LCD readouts will be shifted by the amount of compensation set, and the photographer must then readjust the aperture and/or shutter speed setting to bring the meter back to the "0" indication to actually achieve the compensated exposure.

To illustrate this, assume you have set f/11 and 1/125 second and the meter scale indicates 0 for correct exposure. If you then set +1 EV compensation, the scale will move 1 EV to the negative side (because the current aperture and shutter settings are now one stop below your desired exposure). Therefore, to achieve the compensation in the actual exposure, you will need to open the aperture to f/8 or reduce the shutter speed to 1/60 second to bring the meter scale back to 0.

Although it is possible to use the exposure compensation feature in the manual mode, it is more practical to use it with the P, S, or A modes because the camera will make the exposure adjustment automatically. In the manual mode, it is much easier to simply shift the aperture or shutter speed by the desired amount directly if you wish to deviate from the metered exposure."