What changes when you dial in exposure compensation?

MatBin

MatBin

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matt
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Puzzling me this one.
I have for instance a 400mm lens wide open, Iso set to 3200 and shutter speed set to 1/1000 but I have dialed in 2 stops of exposure compensation (I need the shot over exposed as there are masses of open blue sky around the subject matter), so the question is does the Iso setting get pushed 2 stops (i.e. up to 12800) or does the shutter speed get dropped to stops (i.e down to 1/250)?
I cant see the aperture changing as it's already wide open, wonder if stopping it down would change how the camera adjusts the exposure.
Info in the shot in Zoom Browser says 1/1000, f5.6 and Iso 3200.
Canon 5d3 with a 400mm prime lens, would the mode make any difference (i.e. aperture or shutter priority).

Anyone got any idea?

Matt
 
The opposite to what mode you are in. If you're in Aperture priority then the shutter speed would be adjusted and vice versa. This is obviously happening in the metering stage so nothing really 'changes' as such.
 
LeeRatters said:
The opposite to what mode you are in. If you're in Aperture priority then the shutter speed would be adjusted and vice versa. This is obviously happening in the metering stage so nothing really 'changes' as such.
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But if I am in Shutter priority and the lens is wide open i.e at F5.6 then the lens aperture cant open any wider and given the exposure is "correct" despite all the blue sky something has to change
 
If you want to understand this try photographing a subject in manual with a metered shutter speed and same aperture in 'manual' and use the EV +/- dial only.
 
Blank_Canvas said:
If you want to understand this try photographing a subject in manual with a metered shutter speed and same aperture in 'manual' and use the EV +/- dial only.
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I understand what the effects of Exp Compensation are, what I cant establish is what changes in the camera operation if I am in Shutter priority mode with a wide open lens, but thanks anyway.
 
Experiment and see! Set to no EC, see what shutter speed the camera decides on with the lens wide open in Av mode then dial in the EC and see what the shutter speed is. In Tv mode, set the EC to 0 again then choose the fastest shutter speed that you can while staying within the lens's widest setting then dial in some EC. Not sure what would change if the ISO was set at a chosen rather than auto value, hopefully you'll report back!
 
I think you'll find the exposure won't change beyond your lowest settings. If you think about it, your lens is wide open, you are asking for more light and you've set your shutter. The only remaining variable is the iso. If you have auto iso on, that'll bump up in proportion to your shutter speed once you've hit wide open aperture. As Blank_Canvas says, have a play in manual.
 
Makes sensor more sensitive
 
MatBin said:
I understand what the effects of Exp Compensation are, what I cant establish is what changes in the camera operation if I am in Shutter priority mode with a wide open lens, but thanks anyway.
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Surely your camera shows you what changes both in the vf and in the exif.
 
It depends on the camera model (I have 0 experience w/ a 5D3), the mode it's in, and if ISO is in auto. But the camera's behavior does not change in any way. The only thing EC does is tell the camera that it's metering is "wrong" so it will adjust for that if it can. The "adjustment" will be exactly the same as if the metered exposure changed w/o EC.
 
Had a bit of a play in the sunshine this afternoon, think I know what is going on now.
First off I set Shutter priority (Tv) with no EC and got F5.6 meter value, I had set the Iso manually, got a "correctly " exposed shot, then dialled in 2 stops over exposure, VF telling me I'm going to under expose (flashing f5.6 at me), picture came out correctly exposed, that is same as first shot. So it looks like the camera does nothing if the lens is maxed out and Iso is manually set.
I guess yesterday 2 stops under exposed got the lens down to f5.6 and the meter thought that was ok i.e. 2 stops away from what it thought was correct.

Then I had a play with auto Iso in Tv mode.
Looks like the camera meters and sets aperture to what it thinks is the correct value in Tv mode i.e. wide open as its first decision, then up the Iso if wide open wont give correct exposure, then finally pushes the Iso up a further 2 stops to give the over exposure I said I wanted.

So for birds in flight I reckon I can set the shutter speed to what I want, set auto Iso on, set 2 stops over expose and the lens will be set as wide open if needs be and the Iso will be set by the camera to what would have been correct without EC being set.

Sun went down, so I will try that some time soon.

Mind you if I had a Nikon or a 1 DX I could set aperture and shutter speed manually, auto Iso and add EC as required, that way I would set the dof I wanted, apparently 5D3 cant do that.


Matt
 
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But if in manual and you've set the iso @100 f2.8 and 1/125 of a second....... If you adjust the ev it will change the exposure........ BUT HOW?
 
sk66 said:
Nope, it's moving the exposure meter indication/display... *You* have to change the exposure to recenter it.
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But what's it changing in camera to make it under or over exposed....
 
Mark twiglet said:
But what's it changing in camera to make it under or over exposed....
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Nothing if the camera is set to full manual... if you are seeing the exposure change, then one of the exposure settings is being changed by the camera (i.e. you are not in full manual).

If you are in full manual, the meter is telling you that it thinks the scene is going to be over/under exposed. And that's because you told it to with EC.

EC is really just a "meter offset"...
 
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I would suggest watching a few videos on the use of exposure compensation to fully understand how it works in Aperture Priority & Shutter Priority, & also to see how ISO relates to the equation based on whether it's set to auto or not.

As Steven says you cannot make use of exposure compensation when in full Manual mode without physically adjusting the setting(s) yourself - manually.
The camera will only adjust settings in one of the auto/semi auto modes.
 
MatBin said:
So for birds in flight I reckon I can set the shutter speed to what I want, set auto Iso on, set 2 stops over expose and the lens will be set as wide open if needs be and the Iso will be set by the camera to what would have been correct without EC being set.
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I don't think so...
Once the aperture has maxed out then the ISO should increase... at all times the exposure should be 2 stops over what it would have been without EC.

I personally don't like using S/Tv mode specifically because it adjusts the aperture first. I almost always would rather have the ISO increase some before I give up sharpness/DOF; especially for BIF.

Here's how I set my Nikons for BIF (at least some Canons behave the same I believe):
I set the camera to aperture priority.
In the menus I set the max allowable ISO and enable auto ISO.
In the same menu I set the minimum allowable SS I want (2x FL typically).
Metering mode and EC are set depending on the subject/scene difficulty... (i.e. spot metering w/w-o EC if easier/better camera).
AF set to dynamic mode/ continuous (AI servo).

When set this way the aperture remains fixed for sharpness/DOF. Based upon the metering the camera will first keep ISO minimum and SS high. As the situation/lighting changes the camera will first decrease the SS to the minimum setting (based on FL/subject/etc). Once it's reached the minimum SS setting, it will then increase the ISO towards the max setting (i.e. ISO 1600 if set). And once it's reached the max ISO setting it will then decrease the SS below the minimum setting.

At this point it's time to start making tradeoffs. Maybe a little subject/wing/BG blur due to lower SS is ok. But if it's not I can open the aperture to bump the SS back up. If I get to an aperture where DOF/sharpness is unacceptable I can increase the ISO setting. And at some point you just run out of acceptable options...
 
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Steve hi, I agree for most people aperture drives the equatíon, But, in my case shutter priority drives it because I find it very hard to hand hold a slow shutter speed and get a non blurred image and the 5D3 won't let me set a fast enough minimum shutter speed ( e.g 1/1500) so I do that by selecting TV and let the lens max out, a 400 f5.6 is sharp enough wide open and I can live with the dof (everything is a compromise after all) then let the ISO sort itself out with EC set at +2 to ensure the background doesn't override the meter.
So we difer in our philosophy in auto mode, but I doubt we will fallout over it
Thanks for your input, if I find my method fails I will try yours.
Matt
 
Exposure compensation just changes the meter sensitivity.

What changes are made depends what mode you are in. If in shutter priority, it will either increase or decrease your aperture accordingly. If in aperture priority it will increase or decrease your shutter speed accordingly. For example, if you're in aperture priority and at f5.6, and your camera is setting 1/125th, then setting +1 exposure compensation will force the camera to use 1/60th. It won't change the aperture, because you're in aperture priority... that's YOUR job.


If in manual, it actually does nothing whatsoever to the settings (unless auto ISO is set)... it will just give you a meter reading that will over/under expose by as much as you want. Even if auto ISO is set, it will not change ISO until it has no other option.


It won't alter ISO, or do anything else... unless you are in a programme mode or have Auto ISO set, and even then, it will only alter ISO when it has no choice - i.e, already at 1/8000th or already at maximum/minimum aperture... but ONLY if you have auto ISO set.


Simple as that.
 
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@Pookeyhead has it spot on.
With one proviso. If you've got the settings maxed already, then changing the exp comp will make no difference.

I fell foul of exactly that on an occasion (I'll blame it on the beer).
I'd set the ISO manually, I was in shutter priority as I wanted to avoid camera shake on a non IS zoom.
Chimped the shot and thought... Hmm, that could do with a a little more light, so moved the Exp Comp to the right, chimped the next, hmm more light needed and kept going until I had +3 Exp comp with no difference.
It then dawned on me that I'd already been at max aperture, so there was nothing the camera could do.

Lessons learnt here were. The camera Will change the settings if it can, won't if it can't and maybe less beer was required. ;)
 
LC2 said:
@Pookeyhead has it spot on.
With one proviso. If you've got the settings maxed already, then changing the exp comp will make no difference.
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Only if you don't have auto ISO set, or ISO is also maxed out


LC2 said:
I fell foul of exactly that on an occasion (I'll blame it on the beer).
I'd set the ISO manually, I was in shutter priority as I wanted to avoid camera shake on a non IS zoom.
Chimped the shot and thought... Hmm, that could do with a a little more light, so moved the Exp Comp to the right, chimped the next, hmm more light needed and kept going until I had +3 Exp comp with no difference.
It then dawned on me that I'd already been at max aperture, so there was nothing the camera could do.
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It could have changed ISO if auto ISO was set. In which case it would have started increasing ISO once shutter speed/aperture was maxed out.
 
Pookeyhead said:
Only if you don't have auto ISO set, or ISO is also maxed out

It could have changed ISO if auto ISO was set. In which case it would have started increasing ISO once shutter speed/aperture was maxed out.
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Absolutely Agree... As i said though, ISO was also set manually.

I guess the point I'm making is that exp comp doesn't do anything magical that you can't do with the settings yourself and any changes it makes will be reflected in the exif.
 
LC2 said:
Absolutely Agree... As i said though, ISO was also set manually.

I guess the point I'm making is that exp comp doesn't do anything magical that you can't do with the settings yourself and any changes it makes will be reflected in the exif.
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This is true. When in manual, it's actually a pretty pointless exercise actually. If you are aware that you NEED exposure compensation, then you can just set the exposure to read +/= whatever on the meter scale when you're making your settings and it does the same thing. When in manual.. using exposure compensation is just adding one more thing to do. If you know you need to open up a stop, just set your camera so it reads +1 on the meter. Why bother setting +1 Exp Comp.. THEN metering to read 0. LOL. Stupid.

It comes into it's own only when using the semi-auto modes.
 
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MatBin said:
I understand what the effects of Exp Compensation are, what I cant establish is what changes in the camera operation if I am in Shutter priority mode with a wide open lens, but thanks anyway.
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Try it and see, look at the exif to see what changes. About six shots out the window should suffice.
 
This is where what Canon call Safety Shift (not sure what other brands call it) will come in to play. If that is enabled in the custom functions, it allow the camera to override your settings if other options aren't available. So if you're in fixed ISO, and Shutter Priority, but maximum aperture isn't enough, it'll override your requested shutter speed and/or ISO so it can deliver the desired exposure. If Safety Shift is disabled, the camera will just get as close as it can and you won't quite achieve the level of requested EC. I think by default it is normally disabled for Canon cameras?

edit: the 5D3 has three options for safety shift: off, Tv/Av (ie. override shutter in Tv or aperture in Av) and ISO (override fixed ISO).
 
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The W said:
edit: the 5D3 has three options for safety shift: off, Tv/Av (ie. override shutter in Tv or aperture in Av) and ISO (override fixed ISO).
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Could be interesting, might try it.
 
Going right back to the beginning I would ask what metering mode your using? I would be using spot metering for shooting birds in flight that way your automatically going to meter for the birds itself and not the sky around it.
 
Mark twiglet said:
But what's it changing in camera to make it under or over exposed....
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The meter reading. If the meter reads x but you have +2 stops of compensation, the adjusted meter reading is x - 2. It then adjusts the camera depending on which mode you are in based on the assumption that there is 2 stops less light than there actually is.


Steve.
 
Pookeyhead said:
This is true. When in manual, it's actually a pretty pointless exercise actually. If you are aware that you NEED exposure compensation, then you can just set the exposure to read +/= whatever on the meter scale when you're making your settings and it does the same thing. When in manual.. using exposure compensation is just adding one more thing to do. If you know you need to open up a stop, just set your camera so it reads +1 on the meter. Why bother setting +1 Exp Comp.. THEN metering to read 0. LOL. Stupid.

It comes into it's own only when using the semi-auto modes.
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Depends on the camera... some can adjust ISO with EC while in manual mode... and it also depends on the subject/situation as to whether that would actually be a benefit.

magicaxeman said:
I would be using spot metering for shooting birds in flight that way your automatically going to meter for the birds itself and not the sky around it.
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Very dependent on the particular bird (speed) and skill, as well as AF tracking... If you can't reliably keep a focus point on the bird then spot metering won't help. I've photographed birds where it was very hard to even get/keep them in the viewfinder (i.e. swallows).
 
My understanding is that with exposure compensation the camera metering 'looks' for a mid-grey. If the whole scene is brighter than mid-tone grey as in a snow scene, the result is grey snow! If you are in a dark place, then the camera tries to 'brighten' the scene and can ruin the atmosphere. So, if the scene is very bright, use +, if its quite dark use -. If its a scene with bright sky and dark foreground, it isn't going to achieve much. Meter for the important bit.
 
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