Circle of Confusion

[JeremyLangford]

What it is?

[cowpix]

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

[Curtis N]

Ain't wiki great?

By reading that article, hopefully you can understand why different camera formats have different DOF properties, why DOF is more of a quantified concept than an absolute, and why DOF can't even be calculated until you decide what size print you're going to make.

Enough to make yer head spin. ;)

[JeremyLangford]

Ain't wiki great?

By reading that article, hopefully you can understand why different camera formats have different DOF properties, why DOF is more of a quantified concept than an absolute, and why DOF can't even be calculated until you decide what size print you're going to make.

Enough to make yer head spin. ;)

holy crap. Ive got a lot to learn. Anyone got some ausome DOF tutorials that they learned off of?

[Curtis N]

Lots of info here, and an online calculator
http://dofmaster.com

Otherwise, wiki is your friend. ;)

But once you determine your camera format and print size (8x10 is sort of the standard), then it all comes down to distance, focal length and aperture. It's not so complex when you narrow things down to those factors you can control. And sometimes you can't control any of them!

[JeremyLangford]

I dont get why print size would matter

[jra]

I dont get why print size would matter
The larger the print, the larger the "circle of confusion". Therefore what would appear sharp in a smaller print will appear OOF on a larger print making the DOF appear more shallow.

[Curtis N]

I dont get why print size would matterTake a look at your own avatar. It looks sharp, from your nose clear back behind your ear. But I bet if you look at the original high-rez version on your monitor at 100%, you'll see the hair behind your ear is not quite sharp (assuming you used a wide aperture and focused on your nose).

DOF quantifies how far an object can be from the focused distance and still look "acceptibly sharp." When you make a print bigger, those areas that are almost in focus become noticeably out of focus.

[Wilt]

Anything in perfect focus is registered as a perfect point (or collection of points). Anything not in perfect focus become a circle with a diameter; the larger the diameter, the more we perceive it to be out of focus. If we magnify everything 4x, the circles increase in size less than if we magnify everything to 20x; at 20x our eyes can more easily determine that all the circles are not points, so more appears to be 'out of focus' at the larger magnification.

Note that the above does also have correlation to viewing distance. So if we increase the viewing distance of the 20x print by 5X, it appears to have the same amount in/out of focus as the 4x print viewed from 1x viewing distance. If you stood right up to the the roadside billboard illustration, you would see what appears to be a horribly focused shot!

This all has to do with the fact that our visual acuity has a finite limit in terms of the angular displacement of any detail which we can perceive. The 4X print viewed at 3' has the same angular displacement for all of its details as the 20X print viewed at 15'.

[oldsquawk]

Circle of Confusion...When 8 or more members of an Internet photography forum sit in a circle and exchange information found on the forum. ;)

[JeremyLangford]

So when light hits are sensor as your taking a picture with a person and a backround blur, Is there just a whole bunch of points that make up the person and a whole bunch of circles that make up the background?

Or is it more like this, where its basically one beam making up the whole picture?

http://i13.tinypic.com/66doujc.jpg

[Wilt]

A scene is not a series of points per se.

But if you took a photograph of a perfect point, in perfect focus, it would appear as a perfect point in the photo. Out of focus, it would appear as a circle whose size is dependent upon how far back from the print you are. Stand back far enough and that circle doesn't seem so big any more, so it seems to be in focus.

[oldsquawk]

But if you took a photograph of a perfect point, in perfect focus, it would appear as a perfect point in the photo.

Actually, this statement is not true. A perfect point of light cannot be recorded as a perfect point due to the laws of physics governing the wave nature of light. The in-focus image of a point of light will be recorded as a "circle of least confusion". The "circle of least confusion" will always be the smallest circle of confusion at the plane of focus.

[Wilt]

Actually, this statement is not true. A perfect point of light cannot be recorded as a perfect point due to the laws of physics governing the wave nature of light. The in-focus image of a point of light will be recorded as a "circle of least confusion". The "circle of least confusion" will always be the smallest circle of confusion at the plane of focus.

You remind me of a fraternity brother who would nitpick and argue points beyond the reasonable, to the absurd. :rolleyes:

For discussion purposes, there is no perfect point simply because the smallest we can resolve today is one pixel, and it is very high odds that any point coincides exactly with both the placement and the size of that pixel...the pixel spreads the size of the point to the full pixel width!:p

[JeremyLangford]

Ok, so when light exposes to our sensors, is it just a whole bunch of in focus and out of focus light points coming from objects, then through our lens, and then into the sensor?

Is it just a whole bunch of light triangles that can vary from any of these three examples?

http://i13.tinypic.com/66doujc.jpg

[Curtis N]

Yep.

You can study optics and and realize it's pretty darn complex, but where DOF is concerned, I think you're getting it.

[JeremyLangford]

sweet. Thanx a lot.

[JCR]

Aha now I understand why the word confusion is used :D

[mrkgoo]

Aha now I understand why the word confusion is used :D

I had to laugh at this :D

Jeremy, that diagram is the first one that has made me 'clik' in understanding corcles of confusion (a mere few seconds ago) - I always had the vague concept, but that kind of cements it for me.

The way I see it now is that it demonstrates what happens when a 'point' is in the DOF, behind it or in front. Anything else at the same distances, say a duck, would have the same 'blur' to it. Not necessarily a 'bunch of points'. Do I understand it correctly?