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Old Nov 7, 2008, 8:28 PM   #1
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Does the 40D exposure compensation really do anything? If I'm in AV or TV mode and dial in exp comp all the camera does is change the shutter speed or Aperature respectively. Just seems like a modified manual mode. Does not seem to be any compensating happening.

If I expose a shot and then change nothing but dial in +2 exp comp I end up with the exact same result. Same goes for -2 comp.

Is this how it's supposed to work?
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Old Nov 8, 2008, 5:15 AM   #2
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MurphyJP wrote:
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Does the 40D exposure compensation really do anything? If I'm in AV or TV mode and dial in exp comp all the camera does is change the shutter speed or Aperature respectively. Just seems like a modified manual mode. Does not seem to be any compensating happening.
Exposure Comp basically allows you to modify the auto mode of the camera. So it is more manual than Avor Tv but not fully manual.

Let me give this example.

If the camera in Av and you set f5.6 and the camera gives a shutter speed1/200th for what it believes to be a correct exposure.

If you now dial in +1 exposure compensation this will over expose from what the camera believes to be correct by one stop so the aperture will stay the same as you are setting that and the shutter speed is not 1/100th.

If you dial in -1 exposure compensation then you will under expose by one stop giving a shutter speed this time of 1/400th.

Going the other way in the same lighting conditions, you are now in Tv and set a shutter speed of 1/200th, this means the camera will select an aperture of f5.6.

If you dial in +1 the camera will selectan aperture of f4 letting one more stop of light in.

If you dial in -1 the camera will select an aperture of f8 thus it is darker by one stop.

Quote:
If I expose a shot and then change nothing but dial in +2 exp comp I end up with the exact same result. Same goes for -2 comp.

Is this how it's supposed to work?
This seems to disagree with what you said in the first part, if the shutter speed or aperture are changing while the one you set is remaining the same then you will have an altered exposure.

An easy way to do this is to shoot at a blank wall, piece of paper or something indoors on a tripod so things are not changing.

Go to aperture priority and select f5.6 and take a shot, this should be a proper exposure (as far as the camera is concerned, if you shoot a dark wall you will think it looks lighter than you would expect, if it is a white wall/paper then it will look grey but that is correct..... I can explain this later if needed but don't worry about that part for now).

Next shoot one at -1 and +1 then -2 and +2 and you will see firstly that the shutter speeds are changing as mentioned and the final result will be different too.

If this is not happening then something funny is happening but I'm sure you will be OK.

Let us know how you get on.

Mark
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Old Nov 8, 2008, 10:45 AM   #3
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Exposure compensation is very simple.

If you dial in +1 it will overexpose by one stop (compared to what it thinks the correct meter reading is).

If you dial in -1 it will underexpose by one stop.

Once you learn how your metering works in different situations it's a very easy way to adjust your exposure for situations where you know the metering will get it wrong.

I've been using Canon matrix metering for a long time. I know how it's going to respond to backlit situations, white skies, snow, etc. So it's very easy to dial in the EC I want.

In fact with digital the Canon metering tends to be a little conservative because they don't want to blow highlights in JPG shots. On my 5D I tend to dial in +2/3 as my default metering for RAW shooting.
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Old Nov 9, 2008, 10:43 AM   #4
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Thanks guys. I'll spend some time experimenting with your suggestions.

Always good advice here.
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Old Nov 9, 2008, 10:45 AM   #5
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You're welcome.

I'm interested to see if there is anything amiss so let us know.
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Old Nov 14, 2008, 7:17 PM   #6
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FWIW, many ofthe Canon shooters I know have EC set to -1/3 as SOP. The theory is that shadows are more easily saved than blown highlights.
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Old Nov 15, 2008, 9:27 PM   #7
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I've not come across the need for under exposing with the canon dSLR range for the reason peripatetic mentions. Are these landscape shooters you are talking about but even so generally canon protects highlighs which is why a lot of people think there is under exposure issues?
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Old Nov 15, 2008, 10:44 PM   #8
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If you are not seeing any change in your pictures using the compensation dial, then check the camera settings in the menu. By default the camera will always try to give you a correct exposure, over riding your settings. Thisfunction can be tunned off using the C/F settings in the menu.
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Old Nov 16, 2008, 6:30 AM   #9
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From a quick skim of Custom Functions for the 40D, I don't see anything that would cause the camera to override your Exposure Compensation settings in any of the modes being discussed where Exposure Compensation can be used (Av Mode, Tv mode, etc.).

If you're looking at Custom Function 1-1, when that's set to 0 versus 1, that's only telling it to use 1/3 stop versus 1/2 stop increments, not to ignore your Exposure Compensation settings.

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Old Nov 16, 2008, 4:08 PM   #10
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It's called Safety Shift, C.Fn 1-6 page 155, works in the Tv/AV modes. Safety shift will change the shutter or aperture as the camera sees fit to get a proper exposure.

JimC thanks forquestioning me (really), I've been meaning to look that function up in the manual and turn it off for months. Thanks to you I finally found it,guess I just neededa nudge.:G
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