Dear Charlie, Philippe,I now see what I had not realized before. In plain language, I was wrong, and had jumped to an improper conclusion. Charlie has made clear what LFI danced around.
I believe that no matter what the size and physics of the sensor may be (film, one of several kinds of electro-optical sensor, etc.), the properties of the light impinging on the image plane is a function of the camera geometry and the lens. Period. I should have stopped there.
What I had not understood was that the DOF (as measured by a circle of confusion of arbitrary size) is not a function of the properties of that impinging light but is a function of what can be recorded by the sensor (film, one of several kinds of electro-optical sensor, etc.).
And now we come to the interplay of sensor dimensions (relative to the 35mm format, which gives rise to what I called the illusion of focal length extension, or crop factor) and the effects of pixel size within that sensor, on DOF.
And at this point I must leave the discussion to others, because I have no knowledge of that interplay. I will leave it to LFI and the physicists to explain that for us. I sense it is not a simple matter.
With grateful thanks to you both, Bill On Nov 13, 2007, at 5:12 AM, <chfalke@xxxxxxx> <chfalke@xxxxxxx> wrote:
Bill, You are right that format doesn't change the DOF for a given lens, but the degree of enlargement affects the permissable circle of confusion, so using a format half the size to make a print of a given size will reduce depth of field. The scales on lenses are based on an assumed circle of confusion based on prints from the full format. Charlie. ---- William Abbott <wbabbott3@xxxxxxxxxxx> wrote:On Nov 12, 2007, at 12:36 PM, Philippe Amard wrote:you might also consider that once on the DMR your lens is no longer70 or 90 but must be multiplied by the crop factor. Hence less of DoF.Philippe, Having given it some thought, I believe that the DOF is a function of lens focal length and aperture, both properties of the lens alone, and an assumed maximum circle of confusion. Thus, DOF is a property of the lens, and is uninfluenced by the camera or the size of the image detection and recording system. For example, if I load my R9 with film and mount a lens, the DOF will be a property of that lens. If I install a DMR, the same DOF will pertain, no matter what size of detector I mount. If the sensor is smaller than the film size, 24 X 36 mm, I will have a smaller image and have the illusion of a longer focal length lens, but the DOF will still be that associated with that same lens. That's the way I understand what is happening. All the best, Bill------ Unsubscribe or change to/from Digest Mode at: http://www3.telus.net/~telyt/lrflex.htm Archives are at: //www.freelists.org/archives/leicareflex/
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