[pure-silver] Re: Depth of Field (35mm vs. 4x5 or 8x10)
- From: Jim Brick <jim@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 29 Oct 2004 09:45:08 -0700
At 11:52 PM 10/28/2004, Michael Healy wrote:
>I'm wondering whether someone might be able to confirm or elaborate upon a
>couple
>questions I've been kicking around, regarding depth of field and lens length.
...
OK.
DOF. Determined by image magnification and f/stop.
A 100mm lens on a 4x5 has the exact same DOF as a 100mm lens on a 35mm
camera, when the two cameras are side-by-side photographing the same
subject. The problem is that the subject area covered by the 35mm camera is
duplicated on a 35mm size patch in the middle of the 4x5 film. The rest of
the 4x5 film has the rest of the world around the 35mm framed subject. A
100mm lens on a 4x5 is a wide angle lens. A 100mm lens on a 35mm camera is
a short telephoto. If you only use a 35mm patch of the 4x5 film, the
cameras produce exactly the same image.
To get the same magnification, a 4x5 camera with a 210mm lens must be 210'
from the subject when the 35mm camera and 100mm lens is 100' from the
subject. The DOF will be the same for both images, but what is seen by the
35mm camera is duplicated on a "35mm patch" on the 4x5 film. Might as well
just use the 35mm camera.
If you wish to put the exact same image filling the 4x5 film as you have
filling a 35mm frame, you have to move the 4x5 camera closer. If the 35mm
camera is 100' from the subject, you have to move your 4x5 camera with
210mm lens to 12.5' from the subject in order to fully frame the same
subject in both cameras. This is 16 times closer to the subject and is the
equivalent of losing four stops of DOF. Shoot at f/11 on both cameras, your
DOF on the 4x5 is equal to shooting at f/2.8 on the 35mm camera. Basically
a disaster.
To obtain the same DOF, you must stop down the 4x5 camera four stops
farther than the 35mm camera. F/11 in the 35mm camera with 100mm lens at
100' filling the 35mm frame with the subject is equivalent to F/64 on the
4x5 camera with a 210mm lens at 12.5' filling the 4x5 frame with the same
subject.
f/16 on the 35mm camera = f/90 on the 4x5.
f/32 on the 35mm camera = f/128 on the 4x5 camera.
For the same frame filling image with the same DOF on both cameras.
Jim
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