DOF is nothing physical in itself. It depends on viewing size, too (i.e. size of COC), besides distance and focal length. Look here, equation 9 and 12: http://toothwalker.org/optics/dofderivation.html .Don Haines said:Mikehit said:Reach is a function of pixel pitch not sensor size. If the pixel density of 5DSR is (give or take) pretty similar to EM-1.2 they both have the same 'reach' with a 300mm lens.
FOV is irrelevant if you are focal length limited.
Exactly!
Look at the 1DX2, the 5DSR, and the 7D2....
Slap a 400F5.6 on each body, stand in the same spot and take a picture of the same object at F5.6....
Let's call the 1DX2 shot the "standard image" to compare against.....
The 5DSR image will have an identical field of view as the 1DX2 image and the DOF will be identical, but the image will be sampled more densely.
The 7D2 image will have only 62% of the field of view of the 1DX2 image, the DOF will be identical, and the image will be sampled more densely.
The fun part is the comparison between the 5DSR and the 7D2..... both cameras have the same pixel pitch and are approximately at the same level of sensor technology... If you crop the 5DSR image to the same field of view as the 7D2 image, the two images should be identical. Same DOF, same sampling density......
Lenses do not magically change properties when swapped onto different bodies. The optics do not change. The photon entering the lens does not know what sensor is at the far end of the lens and can not change it's path based on that.....
DOF does not change because you have moved between crop and FF. DOF changes when you walk closer (or further) from your subject (framing) or when you change the aperture of the lens.
As the COC is differently taken for both formats, DOF decreases for APSC in case of same focal length, aperture and distance, as we want the same relation between diagonal and COC, which is confirmed by a dof calculator, as long as you print to the same sized image!
Zeiss: "The size of the object field is reduced by the crop factor while the object-side light cones remain the same, as long as we use the same lens and do not change the aperture setting. That is why the points of the light cones may not be located so far from the focal plane if we want to maintain the same ratio of diagonal to circle of confusion. Reducing the size of the film format therefore reduces the depth of field by the crop factor."
Use http://dofmaster.com/dofjs.html to check it: e.g. 85mm/f2 at 5m distance. DOF = 27.2 cm (APSC) and 40.9cm (D800).
Only when viewing the APSC image at a smaller size related to the crop factor, your DOF will be the same. The important thing is the size of the COC relative to the size of the sensor, to get the impression that a point on the object side is projected within the COC to be still seen as a point in the image plane.
If you crop the FF image to APSC, you change the magnification which goes into the DOF equation as 1/M^2, influencing the perceived DOF (for same output size). The larger you display the image, the more obvious it will become that deviations from the "plane of perfect focus" are out of focus, and the smaller you display the image, the less obvious it will be. So what is appearing to the human eye to be in focus is dependent on viewing size (and therefore cropping and magnification) and distance to the print/image, which is used to define COC, which then determines the DOF.
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