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T2i - Exposure and Press Shutter Button Halfway Down

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Steve Crow
T2i - Exposure and Press Shutter Button Halfway Down
on Jul 30, 2010 at 7:57:03 pm

I am not understanding what is happening when, while in Movie Mode I press the shutter button halfway down.

What I see is that the marker below the exposure compensation ruler blinks.

What I have been doing is if this marker is showing an "overexposure" like +2 I use the AV+/- button and the scroll wheel to move the marker back to the middle...is that what I am supposed to do or am I misunderstanding how it works.

Basically - is this how the camera is "hinting" me to "correct" my exposure


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Michael Sacci
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Jul 31, 2010 at 12:07:50 am

Yes that is what it is telling you.


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Steve Crow
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Jul 31, 2010 at 12:56:09 am

Thanks Michael, I hope you don't mind some additional questions about exposure.

First off, what does the camera consider "correct" exposure? How does it arrive at the conclusion that I am over, under or just right exposed? I consider exposure to be mostly an artistic, versus a technical choice, but the camera must have some measurement-driven formula to decide what is "correct" exposure and what is not.

I did some quick experiments to find out in more detail what is actually going on when I move the marker of the exposure compensation ruler back to middle.

In my experiment I found that the camera changed my shutter speed in order to get the exposure IT wanted. I, however, wanted to keep my shutter speed as is so I instead changed the ISO or aperture to get the same effect as what the camera wanted.

Do you think it would ever change the ISO or f-stop as I move the marker or does it only change the shutter speed?

Last Question, if I want to purposely under expose a shot for example, do I again use the same AV button and scroll wheel combo but this time move the marker to the left of the middle of the ruler by one or two or three stops?


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Andrew McKee
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Jul 31, 2010 at 10:38:08 am

A camera doesn't know what your scene is like. Any exposure reading will just be based on the average brightness it is detecting and so should always be taken with a pinch of salt. If a camera is in automatic mode then it will automatically adjust the aperture, shutter speed and iso to get as close to that "correct" exposure as possible. You can usually effect what it changes, by going into a different mode. Aperture priority mode, for example, will maintain your selected aperture and just change shutter speed and ISO. Ideally you should be in full manual mode (certainly for video work) and that choose what balance of aperture, shutter speed and ISO is right for you scene (although generally video work usually keep shutter at half your frame rate for consistency of motion blur).

Andy


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Bill Doyle
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Jul 31, 2010 at 3:48:40 pm

Steve,

Your best bet is to shoot everything in manual so that you have full control. In addition, you should set the shutter to double the setting of your frame rate. (If your using 24P, use a 1/50 shutter.)

Bill


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Steve Crow
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Jul 31, 2010 at 6:02:37 pm

Yes I agree with everything Bill and Andy said. But when I shoot in full manual mode and use the AV button/scroll wheel combo to adjust my exposure to what the camera is suggesting, it changed the shutter speed.

Being in video mode on full manual I didn't have aperture priority or any other mode like that in operation so it's interesting to me that the camera opted to change shutter speed (which I changed back by the way)

In other circumstances would the camera have changed the ISO or aperture? I may have already been at the lowest ISO when this test was conducted - so maybe it has some kind of order it goes though to change the exposure like "first try ISO, if you can't do that try shutter speed and if that can't be changed then adjust the aperture."

Like I said, I don't know the camera's logic I am just trying to understand it.


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Michael Sacci
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Aug 1, 2010 at 1:04:40 am

I would hope that the camera would never change the shuttle speed. For video that is off limits. As stated above anything other than double the frame rate produces an effect to the video, so unless you want a look it need to be locked down.

This is why I variable ND filter is a must for video work when you have no control over the lighting.

THe only time I would use auto is if I would just shooting fun stuff.


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Darrell Beck
Re: T2i - Exposure and Press Shutter Button Halfway Down
on Aug 2, 2010 at 12:04:13 am

When you press the shutter half way down in video mode, the camera is looking for contrast to auto focus. If it does not have enough, it is going to increase the gain (iso) to aid in focusing. When it is complete, it will return to your setting.

I do use the exposure guide on the bottom of the screen, but only as a guide. I really wish this camera had zebra or a histagram.


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