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A Sfeir

New lenses and the future of FF

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I think this site should be set up to automatically delete an entire thread if the phrase "depth of field" and "crop" appear in the same post. We've beaten that subject to death....

Err, yes Andy, it appears to be the most complicated part of photographic theory. I thought I had written a definitive post on it about three years ago, Stephen has written a far superior treatise on the subject, many threads have thrashed this thing out, and still all the old misconceptions keep popping up. One consolation: The threads on how to run the Leica Company are even more persistent...

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....here in Holland, 'Depth' of field can also mean the pump has broken down!

 

I'm just the boy with his finger in the dyke, trying to hold back the flood of DoF theories...

 

8^)

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Probably the best explanation: (go to link for diagrams)

 

Understanding Depth of Field in Photography

 

Excerpt:

..."Depth of field is the range of distance within the subject that is acceptably sharp. The depth of field varies depending on camera type, aperture and focusing distance, although print size and viewing distance can influence our perception of it. This section is designed to give a better intuitive and technical understanding for photography, and provides a depth of field calculator to show how it varies with your camera settings.

 

Depth of Field Example Image Depth of Field

 

The depth of field does not abruptly change from sharp to unsharp, but instead occurs as a gradual transition. In fact, everything immediately in front of or in back of the focusing distance begins to lose sharpness-- even if this is not perceived by our eyes or by the resolution of the camera.

CIRCLE OF CONFUSION

 

Circle of Confusion Diagram

 

Since there is no critical point of transition, a more rigorous term called the "circle of confusion" is used to define how much a point needs to be blurred in order to be perceived as unsharp. 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." The circle of confusion above has been exaggerated for clarity; in reality this would be only a tiny fraction of the camera sensor's area.

 

Visualization: Circle of Confusion

 

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.

Depth of Field Markers on a Lens 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.

 

A different maximum circle of confusion also applies for each print size and viewing distance combination. In the earlier example of blurred dots, the circle of confusion is actually smaller than the resolution of your screen for the two dots on either side of the focal point, and so these are considered within the depth of field. Alternatively, the depth of field can be based on when the circle of confusion becomes larger than the size of your digital camera's pixels.

 

Note that depth of field only sets a maximum value for the circle of confusion, and does not describe what happens to regions once they become out of focus. These regions also called "bokeh," from Japanese (pronounced bo-ké). Two images with identical depth of field may have significantly different bokeh, as this depends on the shape of the lens diaphragm. In reality, the circle of confusion is usually not actually a circle, but is only approximated as such when it is very small. When it becomes large, most lenses will render it as a polygonal shape with 5-8 sides.

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I don't understand Difraction; for example, if you take the sensor resolution to infinitum do you still have difraction? if, you use the new 24/1.4 at 1.4 in this sensor with infinit small pixels, is there still difraction at some point? is the difraction of a 35/2.8 mf lens at 2.8 different to the difraction of a 35mm 35/2.8 also at 2.8?

 

If someone is pasient enough to give an answer to this questions, I'd be very much abliged.

 

Gero

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