DotTune: Video Tutorial for AF tuning without photographs

Started Feb 18, 2013 | Discussions thread
TOF guy
Forum ProPosts: 10,709Gear list
In reply to lock, Feb 23, 2013

lock wrote:

"When the circle of confusion becomes perceptible to our eyes, this region is said to be outside the depth of field and thus no longer "acceptably sharp."

"When does the circle of confusion become perceptible to our eyes? An acceptably sharp circle of confusion is loosely defined as one which would go unnoticed when enlarged to a standard 8x10 inch print, and observed from a standard viewing distance of about 1 foot."

At this viewing distance and print size, camera manufactures assume a circle of confusion is negligible if no larger than 0.01 inches (when enlarged). As a result, camera manufacturers use the 0.01 inch standard when providing lens depth of field markers (shown below for f/22 on a 50mm lens). In reality, a person with 20-20 vision or better can distinguish features 1/3 this size or smaller, and so the circle of confusion has to be even smaller than this to achieve acceptable sharpness throughout."

So it is a somewhat loosely defined yet standardized concept, but basically it depends on our perception as desribed in the last two sentences.

Add to this: "...DoF concept: it only accounts for the total DoF and not its distribution around the focal plane, even though both may contribute to the perception of sharpness"

DOF is based on the choice of a circle of confusion. A point which is not on the focal plane will become a motif which is two dimensional on the print. This point is within DOF if the blur is less than the circle of confusion. It is outside if the blur is bigger.

That's all there is to the definition of DOF (although some have come with more sophisticated definitions but they all come down to an objective set of conditions for which a subject is deemed within DOF).

Of course the numerical value of the CoC is based on the estimate about how small the blur can be to be unnoticed by our eyes.

It's in the sentences you point to although IMO they are misleading in the sense that they may let you believe that DOF is an actual prediction of perception.

Here is a better link .

Actually addressing perceptual vision is impossible through such simple concepts. Again "if the eyes are sharp and the ears noticeably OOF the picture looks sharp" but "if the ears are sharp and the eyes are very slightly misfocused the picture does not look sharp", perception of detail depends on contrast, depends on lighting conditions, on the individual's vision, on how much carotene you've eaten the day before etc. Try to put this into an equation.

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Thierry - posted as regular forum member

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