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Old Jun 12, 2005, 5:18 AM   #1
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Hi, a new member here.

I recently bought a EF 50mm USM f1.4 lens for both my 20d and used to for some portraits. The photos looked fine when viewed on the camera's LCD, sharp and in focus.

In photoshop, again the photos look sharp, however, when I zoomed in the sitter's face looked slightly out of focus almost as if it had been taken with a soft-focus lens.

Zooming in on the camera's LCD also showed the same effect.

Since then I have compared photos taken using other lens and the 18-55mm EF-S lens produces a much sharper image, but another USM lens also seemed to be slightly out of focus.

Now my question is because the EF lenses are attached slightly further away than the EF-S lens? Or is it something more serious?

The 50mm lens photos were taken on the manual setting at ISO100, in in-door light and at f-spot of between 1.4 and 2.

The problem is easily corrected in Photoshop, and the photos printed at about A5 without the soft-focus being noticeable.

Any thoughts and suggestions, much appreciated.

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Old Jun 12, 2005, 5:39 AM   #2
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An aperture of f1.4 gives a very shallow DOF.

If you post some pictures here we could have a look, but the DOF is so shallow at those apertures that you might easily have one eye in focus and one out of focus if the person is looking at a 45-degree angle to you.

http://www.dofmaster.com/dofjs.html

On the 20D/XT for example at a distance of 6ft your DOF is a little less than 1 inch in front and behind your focus point.
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Old Jun 12, 2005, 5:47 AM   #3
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IMO this is not an issue: "Now my question is because the EF lenses are attached slightly further away than the EF-S lens? Or is it something more serious?"

Folks change this distance even greater when they attach an extension tube...
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