EOS 300/Rebel 2000 depth of field button

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After reading answers to previous similar questions, I'm still not 100% on the depth of field button on my EOS 300. When I use a small aperture and press the depth of field button, the picture appears darker. Does this mean that if I take this photo, it will turn out this dark?

Also, how do the multiple exposure photos work? Is it just the subject in focus which is imprinted each time, or is each whole picture imprinted onto the same section of film?

-- Jodi (dalle777@yahoo.com), December 29, 2001

Answers

1) No, the picture will not turn out dark. The shutter will remain open longer to allow the correct amount of light for a correct exposure to reach the film.

2) The entire picture is exposed. A 35mm camera is incapable of doing anything else. Thus, to correctly expose the film, you will need to use exposure compensation so that each individual picture is under-exposed. However, multiple exposures are very, very rarely useful.

-- Isaac Sibson (isibson@hotmail.com), December 29, 2001.


1) That is exactly how the lens will be at the moment of exposure. Normally, when you look through the viewfinder you are looking through the lens with it's aperture blades in the open position (f/3.5 for example). This is done so that you get a nice, bright view. However, when you trip the shutter button it is then that the aperture blades close down to the actual setting set by you or your camera (f/8, f/11, f/16, etc.). This action is occuring every time you shoot a picture. Pressing the depth of field preview button simply causes the aperture blades to close down as they would at the time of exposure, without actually taking the picture. Remember that exposure is a factor of both aperture size and shutter speed. When using a small aperture (f/16), as you can see there is less light coming through the lens, hence the darkened viewfinder. Therefore, a longer shutter speed is necessary to compensate for this. In aperture priority mode, the camera will automatically assign the appropriate shutter speed for the selected aperture size to give you the correct exposure.

2) With multiple exposure photos, the whole image is imprinted onto the same section. How would it be possible to only imprint the subject in focus and ignore the rest of the image? You may be thinking of multiple exposures done with flash photography. In those cases, you can have the background very dark and only the foreground subject illuminated. Because the background is so dark, it doesn't imprint on the film. Only the illuminated subject does. When the illuminated subject moves to a different position for another shot, he/she is again imprinted on the film but the dark background does not. Eventually, you can have multiple images of the illuminated subject against a darkened background.

-- PeterP (pphan01@hotmail.com), December 29, 2001.


The thing everyone's missed from point 1) is that when you push the DOF button the viewfinder shows the areas of the picture that will be in focus when the picture is exposed.

Roughly speaking the larger the f number the more of the picture will be in focus (more accuratly the depth of field widens about the focusing point; this is what DoF preview shows you). You just have to squint a bit in the darkness to see it!

-- David Cuthbertson (david.cuthbertson@btinternet.com), January 15, 2002.


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