Need some explanations about exposure compensation

[Tom3]

I need to understand something:

the exposure being a combination of the ISO, shutter speed and aperture, at which point does the exposure compensation work?

Is it merely post processing from the original data before being saved to jpg? I havent' tried but, in that case, does it even do something to the raw picture?

 

[rufus5150]

Exposure compensation depends on what mode you're in. (The following assumes you're using a fixed ISO because I've no idea how auto-iso works.)

If you're in Aperture priority, adjusting the exposure compensation will increase or decrease the shutter speed.

If you're in Shutter priority mode, adjusting the exposure compensation will increase or decrease the aperture.

If you're in 'P' mode (on canon cameras, at least), it will try to recalculate both the aperture and shutter speed to maintain its 'optimal' parameters for getting you a reliable shot.

It is definitely not done after the image has been captured. It directly affects your exposure settings when the image is taken.

 

[Turnerea]

I need to understand something:

the exposure being a combination of the ISO, shutter speed and aperture, at which point does the exposure compensation work?

Is it merely post processing from the original data before being saved to jpg? I havent' tried but, in that case, does it even do something to the raw picture?

It depends on what mode you are in. Assuming you aren't using some function that allows auto-ISO, then your ISO is set. Then if you are in Av (aperture priority) the camera takes your exposure compensation into consideration when calculating the shutter speed. The same, but just switched for Tv (shutter priority). In manual exposure compensation is not used, as you are choosing both aperture and shutter speed... and the ISO is set as well. So you basically dial in whatever compensation you'd like in manual, hence its flexibility...

 

[kundalini]

In manual exposure compensation is not used, as you are choosing both aperture and shutter speed... and the ISO is set as well. So you basically dial in whatever compensation you'd like in manual, hence its flexibility...

The bold above is incorrect. The camera is trying to meter for 18% grey. If you're shooting snow or coal (in manual), then if you don't add or subtract (+/-) compensation, then each subject will be grey.

Basically, if your subject is darker than the background, add EV (+) and likewise in reverse, take away EV (-) if your subject is brighter than the background.

 

[rufus5150]

I don't even have a way to get to the exposure compensation values when I'm in manual mode. The main wheel modifies the shutter speed, the shift-main-wheel modifies the aperture. I can certainly under-expose or over-expose in 3rds of stops, but the EV just becomes a process of reading the meter.

Other cameras may differ, but that statement is certainly true for mine (rebel xti)

 

[tsaraleksi]

The bold above is incorrect. The camera is trying to meter for 18% grey. If you're shooting snow or coal (in manual), then if you don't add or subtract (+/-) compensation, then each subject will be grey.

Basically, if your subject is darker than the background, add EV (+) and likewise in reverse, take away EV (-) if your subject is brighter than the background.

While this is true, a lot of people get confused about the use of EC in manual mode, not really understanding the way that the you have to simply pick the exposure you like best, as opposed to the way it works in the other modes.

 

[kundalini]

Sorry rufus...... shudda stated this was for a Nikon, but I figured the functionality was universal. My bad.

 

[Tom3]

so, if I understand correctly, it merely change whichever setting is not locked, in all modes but manual, in order to adjust the exposure.

however, I do not understand what happensa in manual? i guess it could change the iso settings, but what does it do if everything is manual, incuding iso?

 

[Photog]

Now I'm confused! In manual mode then, if your camera has an option to change EC, surely this is effectively just changing the calibration on the meter - shifting it left/right, and then you are the one who compensates for this different metering by adjusting shutter speed/aperture? Yes/no?

 

[Turnerea]

Maybe this functionality is different in Nikon, but the fundamentals will remain the same.

In manual mode you have full control, so you can get the same results of having used exposure compensation with Av or Tv, but you're not really using it "exposure compensation"- you are dialing in whatever exposure you want directly- not compensating a definite number + or - from the reading like you do in Av or Tv mode.

To the original poster- your statement about what happens in Av and Tv is correct- just adjust the one you aren't setting. Hope this helps clear up what happens in Manual... I'm an engineer too... I think about it this way- when I'm using exposure compensation that's one equation used to pin down the three variables (aperature, shutter speed, iso). When in manual you don't have this equation relating aperture+shutter speed, so you need to dial in both the aperture AND shutter speed to make up for losing one equation....

 

[Kegger]

I just use it to tone down exposure on my camera, as it shoots to the left as it is. So -.07 EC evens everything out. So you can look at it as a fine tune for the sensor.

 

[Tom3]

ok, this seem to make sense now.

I'll do some tests to see what it does in full manual; maybe it doesn't do anything then on my camera (Nikon D200)

 

[Big Mike]

Shooting in manual or any of the auto modes isn't any different in terms of exposure.

If you adjust the EC to be one stop above the meter or if you set your manual settings to be one stop above the meter...the exposure is exactly the same.

A shot taken at F8, 1/125 & ISO 100 will be the same, no matter what mode it is in.

 

[Turnerea]

Shooting in manual or any of the auto modes isn't any different in terms of exposure.

If you adjust the EC to be one stop above the meter or if you set your manual settings to be one stop above the meter...the exposure is exactly the same.

A shot taken at F8, 1/125 & ISO 100 will be the same, no matter what mode it is in.

Very true... I was just trying to separate the use of "exposure compensation" from manual mode. At least how my Canon works, "exposure compensation" is you telling the camera: deviate from your meter reading +/- "this much". Whereas you don't do this in manual mode- you just dial in whatever you want directly.

The comment before about +1 for snow, -1 for coal... very true- just two different ways to achieve it. Either set the exposure compensation and use Av or Tv mode, or use manual mode, and in choosing your aperture/shutter speed, choose it so it corresponds to +1 or -1, or whatever you need.

 

[Tom3]

A shot taken at F8, 1/125 & ISO 100 will be the same, no matter what mode it is in.

I think I need to rephrase the question:

if I set F8, 1/125 & ISO 100, in manual mode with nothing automatic; then, I select EC +1, what does the camera do?