Archived posting to the Leica Users Group, 2003/04/24
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At 11:08 PM -0500 4/24/03, Clive Moss wrote:
>On Fri, 25 Apr 2003 10:10:43 +0800, Red Dawn <reddawn@singnet.com.sg> wrote:
>
>...
>>
>>u got me wrong. Wat i was comparing was using a Canon 50mm f1.4 lens on a
>>digital SLR like the EOS 10D, where the effective focal length would be 50 x
>>1.6 = 80mm, versus usng a true 80mm lens like the Summilux R 80 f1.4 on a
>>Canon EOS 1v film body, or a R8 for that matter.
>>
>>BOTH configurations will have the same angle of view, and will be able to
>>frame the same subject with the same composition and magnification, and
>>produce pictures with the same DOF.
>>
>>Hence this thing about digital not being able to get enough shallow DOF is
>>simply a fallacy. With digital SLRs that are not full frame, you got to
>>change your mindset - a 50mm lens is NO LONGER a 50mm lens and does not give
>>a field of view of a normal 50mm lens anymore!!!!!!...
>
>Forget about digital, for a moment. The concept of "effective focal
>length" is kinda bogus. The focal length of a 50mm lens is 50mm.
>Period (to be repetitive). Take a picture with a 50mm lens on a
>regular 35mm camera with a 24x36 image frame, and crop it down to
>the field of a digital sensor, what you have is a cropped image from
>a 50mm lens. Cropping does not change the focal length, effective or
>otherwise. Now, do not move the camera (assume it is on a tripod).
>Remove the 50mm lens and put on the 80mm lens (or use a zoom lens
>:-)). You get an image with the same composition, 1.6x (or so)
>larger -- but with reduced depth of field, based on my memory and
>experience.
>
>I have in the last few minutes tried an approximation to this
>experiment using a Canon G3, and zooming instead of changing lenses.
>Guess what -- the results validate the theory. Without moving the
>camera, the depth of field at the longer focal length was
>dramatically less then that at the shorter length, after adjusting
>the images to the same apparent size. Gee -- why am I surprised? I
>was a mathematician!
>
>Try it yourself using your own camera and lenses. You will be convinced.
>
>--
>Clive
Exactly!
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* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com
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