Wednesday 22 April 2009

Canon EG-S focusing screen

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Another recent question:

Hi David,

Like you I enjoy using fast apertures for portraits. I am considering the EG-S focusing screen so I can see the DOF in the viewfinder. I understand you've used one on your old 5D (I think you mentioned it in another post). My question is as these are designed for lenses F2.8 or faster - does stopping one of these lenses down give you the darker image problem you would have if you used a default F4 or slower lens? Or does a darker image only apply if your lens is default F4 or above?

Thank you!


Hi Ricko,

The EG-S focusing screen is only designed to help you with manual focus. It makes it easier to see when a subject is properly focused. It won't give you any benefit in visualising DOF. To do this you'll still need to press the DOF preview button adjacent to the lens release button on the front of the camera.

When you look through the viewfinder the lens is always set to its widest aperture to allow the maximum amount of light in. It only stops down to the aperture you've selected for your exposure when you fully depress the shutter release button. Hence the reason that a DOF preview button is available (though I have to say I don't find it very useful).

The EG-S screen will transmit less light, hence it's recommended that you only use it with a lens with an aperture of f/2.8 or below. For slower lenses the viewfinder may be unacceptably dark.



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