what does exposure compensation really do?

[roshani]

It is becoming force of nature to tweak my exposure compensation dial to get my image where I'd like it, but the more I think about what it does, I realized I am not really sure.

I kinda figured it might be one of two things. It could truly be changing the aperture for me, though if I am at f4 on my 24-105 f4, then there's not much more to open. So thus I kinda figure perhaps it's just a sensor sensitivity thing more like an iso setting. I guess this second thing would be analogous to the old film days when you could push 100 iso film to 400?

This brings to the second point. I often shoot aperture priority or shutter priority depending on what I am shooting to get assist on exposure from my camera meter. If I am at f8 and say 1/250th. If I feel I need to tweak my exposure, which is better, go to full manual and tweak from the settings I just gave, or use my trusty exposure compensation dial?

thanks in advance!

[Jake]

If you are in aperture priority then the EC will change your shutter speed + or -. If you are in shutter priority then it will change you aperture + or -. If you are maxed out on your aperture(wide open) when you are on shutter priority, then the EC wont do much at all on the + side.
The Canon cameras won't adjust the ISO with EC. At least not the 20D or 5D. I'm not sure about the 1 series.

If I'm using flash, then my cameras are on manuel 100% of the time. If I'm shooting available light then I'm about 50% aperture priority and 50% manual.

[kenw]

The simplest way to keep the T and A you want but still tweak is to adjust the ISO. As Jake mentioned, EC won't do ISO for you. I shoot in Tv predominantly (lots of moving things...), so the EC normally adjusts the Av (Aperture). If it tweaks it out of my comfort zone, I'll goose the ISO until I can have my cake (Tv) and eat it (Av) too.....

[Dobick]

The way that I understand it (may be completely off base)

Exposure compensation merely adjust the sensitivity of the meter. It doesn't really change any of the settings...

Let's say that you are outside shooting an 18% grey wall in direct sunlight. With no EC you would meter on the wall, and your camera would tell you that the preferred setting for proper exposure would be 1/125, f/16, at ISO 100. If you adjust the EC down a stop, it is either going to tell you to be at 1/250:f/16 or 1/125:f/22. It merely changes the way that it meters the scene, not really any of the actual settings.

[roshani]

thx guys.

Jake never thought of it the way you stated, aperture is fixed EC tweeks shutter speed. Feel kinda like a do do now that I see the response though, kinda like a duh moment, i.e. thats how i tweek my exposure normally in full manual!

[venchka]

Originally Posted by Dobick

The way that I understand it (may be completely off base)

Exposure compensation merely adjust the sensitivity of the meter. It doesn't really change any of the settings...

Let's say that you are outside shooting an 18% grey wall in direct sunlight. With no EC you would meter on the wall, and your camera would tell you that the preferred setting for proper exposure would be 1/125, f/16, at ISO 100. If you adjust the EC down a stop, it is either going to tell you to be at 1/250:f/16 or 1/125:f/22. It merely changes the way that it meters the scene, not really any of the actual settings.

Not quite Grasshopper. EC actually changes one of the variables, shutter speed or aperture. If the body also does auto bracketing, you can set the camera to shoot +, 0, - by however much you want. On my ancient bodies, one goes in 1/2 stops up/down to a total of 2 stops. The other body goes in 1/3 stops up/down to either 2 or 3 stops, don't remember exactly.

[Dobick]

But you can shoot in manual, and still dial in EC, in which case it doesn't really change the settings? So in my above example of sunny 16 rule, your camera would still be set at 1/125:f/16, but the exposure bar would be showing that you are under or over exposed based on the EC dialed in, but would not change any of the settings.

If you are shooting Av or Tv, you are necessarily allowing the camera to make the choice based on the internal camera meter, regardless of whether you have EC adjusted or not, so the criteria which the camera makes the choice on changes, not the way in which it chooses.

Semantic difference maybe... I think we are saying the same thing.

[venchka]

Say what????????????? Grinning.

I reckon. All I know is, on my EOS-1 I can use Aperture Priority and spin the big knob on the back and run the exposure index pointer up and down the 3 stops over/under exposure scale beside the image in the viewfinder. And see what f-stop & shutter speed is set by looking below the image.

[Rick]

This is worth reading....

http://www.earthboundlight.com/photo...pensation.html

Rick