Busting the FF vs Crop DoF Bokeh Myth

Started Jul 27, 2009 | Discussions thread
Cheburashka Regular Member • Posts: 297
Re: try outdoors

coldbivy wrote:

Sorry, but you are wrong. Indoors or outdoors. Think of it this way. The same lens is projecting the same image circle at the plane of the sensor. The "crop" sensor is smaller, but in the same location as the FF sensor. The "crop" sensor is seeing the exact same image with the same DOF and bokeh, it is simply cropping the image compared to the FF sensor (that is why it is called a crop sensor). The ONLY thing confusing the results presented here is the pixel density. If we repeated the experiment with two cameras with identical pixel density, you'd see that the OP is correct. (I think a 30D and a 5DII should be very close to the same pixel density).

Pixel density has nothing to do with DOF:


It is important to note that the DOF depends neither on the number of pixels that make up the image nor the sharpness of the lens. This misconception comes from the fact that more pixels and/or sharper lenses usually resolve more detail. However, the resolved detail is independent of the DOF. A simple way to visualize the difference between DOF and resolved detail is to apply a Gaussian Blur to an image. While the blurred image will have less detail, the depth from the focal point that is considered to be in focus will be unaffected. So, while DOF, sharpness, and detail are all intertwined, they are independent quantities. A good way to understand this is to imagine an image taken of the same scene from the same position with the same framing and aperture using cameras with very different pixel counts. Now resample both images to the same dimensions so that they just fit on your computer monitor. The DOFs will be the same. It would be no different when printing the images, so long as they were printed with the same dimensions. So, just as detail cannot be changed with sharpening, DOF cannot be changed with more detail.

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