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Old Dec 25, 2008, 3:36 AM   #1
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Iboughta Leica[/b] R to EOS adapter from CAM.PLUS from Hong Kong on
ebay http://stores.ebay.co.uk/camplus-shop.

Itwas $13 and is a perfect fit for all lenses[/b]. It has a stop to
prevent overwinding the adapter ring onto the EOS mount. And nothing,
even the 19mm comes anywhwere near the EOS mirror. So I consider
myself lucky.

My question now is - as the Xsi 450D has the APS-C with the 1.6x factor,
does this change the DEPTH OF FIELD characteristic of whatever manual
lens is on it? Or is the image just simply 'cropped'

The 19mm (on a 35mm camera) is effectively fixed-focus depth of
field it's so large at anything above f4. On the 450D will it change
to that of a 28mm lens??


This is a pano of 4 shots with the Elmarit 35/ f2.8

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Old Dec 25, 2008, 1:08 PM   #2
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Yes, the image is simply cropped.

But, cropping an image changes the depth of field, much of the confusion and animosity arising in forums when DOF is discussed arises from not understanding that if you cut a print in half you have changed the DOF. This may sound weird and counter-intuitive, but is simply a fact derived from the mathematical definitions of CoC and DOF.

Quick summary: DOF is always calculated with reference to a given Circle of Confusion. This is the size at which a dot becomes percieved as a circle under certain conditions.

CoC is calculated with reference to the following parameters:
  1. Viewing distance[/*]
  2. Print size[/*]
  3. Visual acuity of the observer[/*]
  4. Enlargement from the original image
    [/*]
The standard CoC values for different formats are set with reference to a viewing distance of about 25cm with a print size of about 8x10.

Then once CoC is known you can calculate DOF with reference to the following variables:
  1. Focal length[/*]
  2. Aperture[/*]
  3. Distance to subject (focal point)[/*]
So when you crop (a print or negative or "crop" a sensor) you are changing the magnification required to get to the standard print size, which means you change the CoC, which has a knock-on consequence of changing DOF.

The commonly cited CoC for a crop canon camera is 0.019 mm.
The commonly cited CoC for a 35mm frame or FF camera is 0.03mm.

http://dofmaster.com has a calculator.

http://en.wikipedia.org/wiki/Circle_of_confusion

An 18mm lens will have the characteristics of an 18mm lens on ANY format, and will never act like a 28mm lens except with respect to field of view.

But as anyone from the film days can tell you an 80mm lens is a very different beast on a MF rig compared to an 80mm lens on 35mm.

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Old Jan 2, 2009, 5:01 PM   #3
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This is with the Leica Elmarit 90mm f2.8 lens, using RAW, monochrome with red filter effect and stepping up in-camera contrast and sharpness.

The circle of theLondon Eye on the horizon shows(even with jpeg) the steeltubes - about 2ft diameter - at a distance of 10 miles.


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Old Jan 8, 2009, 11:35 AM   #4
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This is the Leica Elmarit 90/ f2.8, -O.7 stop, 100 ASA with the EOS Xsi 450D back. Distance about 10m

cropped from the full 12M pixel jpeg.
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