Questions on "FE Lock" and "Depth of Field Preview"


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AlvicTay

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Hi guys

Some questions when i'm going through the 300D manual.

1. When and what is the use "FE Lock"?
2. When and what is the use of "Depth of Field Preview" button?

Pls help... Thanks!


Cheers
 

nickmak

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FE lock: To lock the shutter speed to allow u to recompose your shot

Depth of Field Preview: When u use a higher f-stop, u can preview the DOF by pressing the button...

Hope this helps!
 

sumball

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nickmak said:
FE lock: To lock the shutter speed to allow u to recompose your shot
Hope this helps!
I would say FE lock will lock your setting such as speed, aperture. i.e. it wont change though the lighting condition has changed when u recompose your shot.

Correct me if I am wrong. ;p
 

Bluestrike

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sumball said:
I would say FE lock will lock your setting such as speed, aperture. i.e. it wont change though the lighting condition has changed when u recompose your shot.

Correct me if I am wrong. ;p
FE Lock; Flash Exposure Lock.
With the AF pt on the subject, press the button and have the flash fired. It will then "remember" the power and duration of the flash thru the calculation etc etc. Then recompose. Even if the AF pt is not at the subject but now aiming at the background, the ETTL will not meter the background but instead uses the "memory" setting and fire. In this way, it ensure that the subject is properly lighted up.

This is from my understanding of FEL.
 

ST1100

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FEL works as stated by Bluestrike above. The one described by sumball is 'exposure lock' (vs flash exposure lock). IIRC they are the same button on the 300D/10D. Some other Canon bodies have them as two seperate buttons.

When you take a flash shot, the flash will meter from the entire scene. If the scene is predominantly black or predominantly white (eg typical wedding dinner scene), the metering will be thrown off. FEL will cause the flash to take a reading from the point either under the the centre area or active AF point - it is up to the photographer to choose wisely which point to meter the flash. Camera assumes the point chosen is middle tone and will adjust the output of the flash *for that chosen point*.
 

AlvicTay

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Thanks guys!

How abt the DOF Preview? Can anyone pls explain more?


Cheers
 

dkw

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AlvicTay said:
Thanks guys!

How abt the DOF Preview? Can anyone pls explain more?


Cheers
According to what I understand, when you look through the viewfinder, prior to triggering the shutter, the lens aperture is actually wide open to allow in maximum light for you to compose the shot and AF to work. This is regardless of whatever aperture setting you use. Try it, stop down the aperture while looking through the viewfinder. If the aperture is stopping down, the image will get darker and darker (it doesn't!). When you trigger the shutter, the aperture will now assume the size you set, the mirror is lifted and shutter opens. By pressing the DOF preview button, the aperture will stop down to your setting, and allow you to visualise the amount of DOF available for that particular setting. Given the small VF on the 300D, I have found this feature next to useless, though somebody on this forum may be able to give you some ideas how to use it fruitfully.

Comments/corrections welcome.

Cheers,
 

bsplenden

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dkw said:
According to what I understand, when you look through the viewfinder, prior to triggering the shutter, the lens aperture is actually wide open to allow in maximum light for you to compose the shot and AF to work. This is regardless of whatever aperture setting you use. Try it, stop down the aperture while looking through the viewfinder. If the aperture is stopping down, the image will get darker and darker (it doesn't!). When you trigger the shutter, the aperture will now assume the size you set, the mirror is lifted and shutter opens. By pressing the DOF preview button, the aperture will stop down to your setting, and allow you to visualise the amount of DOF available for that particular setting. Given the small VF on the 300D, I have found this feature next to useless, though somebody on this forum may be able to give you some ideas how to use it fruitfully.

Comments/corrections welcome.

Cheers,
i never knew how to use this function... don't understand how to use it. can anyone help... when i have a smaller aperture and i press the DOF preview button, my viewfinder becomes darker in poor lighting conditions... so how does this tells me the DOF?
 

goering

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The image you see when you look through the viewfinder is with the lens wide open. This is to enable the viewfinder to be as bright as possible.

When you hold down the DOF preview button, the lens will actually stop down to enable you to look through the lens at whatever f/stop you have chosen. You should be able to see what is out of focus in the foreground and background and how much in-between is in focus.

To clarify further, suppose your lens has a max aperture of f4 and you
compose a shot at f/5.6, what you see in the viewfinder is still wide open but when you press the DOF button, it will stop the lens down to f/5.6 and you can see what f/5.6 will look like in the viewfinder

The main issue to this is that the smaller the lens opening, the darker the image and the harder it is to see anything. Because of this, many of the better lenses have the DOF scale on the lens itself. Those distance markings on the lens are for the DOF scale
 

goering

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dkw said:
Given the small VF on the 300D, I have found this feature next to useless, though somebody on this forum may be able to give you some ideas how to use it fruitfully.

Comments/corrections welcome.

Cheers,
There was a tip from another forum

Hold the DOF button down with the lens at it's widest aperture, and then slowly stop down to your desired setting. This allows your eyes to adjust a little easier to the decreased light, plus it's easier to see what comes in to focus at what aperture, especially on smaller viewfinders
 

Bluestrike

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DOF; Depth of Field.

QUOTE from Canon EF lenses website.
The area in front of and behind a focused subject in which the photographed image appears sharp. In other words, the depth of sharpness to the front of sharpness to the front and rear of the subject where image blur in the film plane falls within the limits of the permissible circle of confusion. Depth of field varies according to the lens' focal length, aperture value and shooting distance, so if these values are known, a rough estimate of the depth of field can be calculated using the following formulas:

More others terms can be found here

Depend on the situation, sometime when we do not or not sure if the Aperature setting that we have can cover the whole subject IE; have the whole face in focus and not only the nose etc etc etc. we can use the DOF button to check that. That is only a rough guide.
 

AlvicTay

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I think georing has a very good explanation! Thanks!
 

sumball

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ST1100 said:
FEL works as stated by Bluestrike above. The one described by sumball is 'exposure lock' (vs flash exposure lock). IIRC they are the same button on the 300D/10D. Some other Canon bodies have them as two seperate buttons.

When you take a flash shot, the flash will meter from the entire scene. If the scene is predominantly black or predominantly white (eg typical wedding dinner scene), the metering will be thrown off. FEL will cause the flash to take a reading from the point either under the the centre area or active AF point - it is up to the photographer to choose wisely which point to meter the flash. Camera assumes the point chosen is middle tone and will adjust the output of the flash *for that chosen point*.
Oh, so sorry... yes I always got confused by this * button found at my Canon body... Anyway, normally I will meter where I want to meter then just switch to manual mode and set my aperture and speed. :D
 

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