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What is "Circle of confusion" Mean ?


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#1 deepak srinivasan

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Posted 13 February 2011 - 02:19 AM

I Wanted to know the meaning for the term "Circle of confusion". i googled and started reading a wikipedia article it was so much of sciene involved i dont want to go deep just for knowledge i want to know exactly what a Circle of confusion means. can some one pls explain it in simple terms ? ? ?

THANKS IN ADVANCE!
CHEERS :)
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#2 Simon Wyss

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Posted 13 February 2011 - 03:08 AM

That’s the circle of confusion: “i dont want to go deep just for knowledge i want to know exactly”

What is it you want?

To know exactly, circle of confusion is the ever present imperfection of an optical lens in projecting a point as a point.

The image of the point is a small circle or disk. Its diameter will be defined by the optical engineer. So far, you don’t want to go deep, do you?
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#3 Chris Millar

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Posted 13 February 2011 - 04:23 AM

Another slightly abstract way of thinking about it is in reverse...

If you place your eye in the film plane and look into a lens you'll see that if its out of focus (which all lens projections are, within a limit of acceptability) - anyway, its projecting more colors than just one, you might even see an inverted image of which all the colours of this image are integrated into the point on the film that your eye is simulating ...

So - lots of colours add up to make the colour of that point - but, how can you reverse engineer that distribution ? you can't ... it's 'confusing'

At the expense of a coherent image at another focal plane :rolleyes: data from the (out of focus) plane you are concerned with is lost
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#4 Chris Keth

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Posted 13 February 2011 - 08:56 AM

Your eyes will render a very small circle as a single point in your mind. The circle of confusion is the measured size of the largest circle on film that will trick your eyes into being rendered as a single point by your brain on the finished viewing format.
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#5 Adrian Sierkowski

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Posted 13 February 2011 - 09:05 AM

Or, as I think of it, how out of focus a small point can really be without looking out of focus ;)

It's a basis for a lot of things, can get a bit confusing, and if you really want to get it, I think you need to go into some detail....
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#6 Brian Rose

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Posted 13 February 2011 - 01:13 PM

I thought circle of confusion referred to those who buy HDSLRs and lens adapters to get that "depth of field look"! ;)
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#7 Adrian Sierkowski

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Posted 13 February 2011 - 01:26 PM

I thought it was a group of producers trying to put together a Alexa.
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#8 Damien Andre

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Posted 13 February 2011 - 02:38 PM

its when a point of light that when entering the lens, the cone of light doesnt land on the image plane at its point, causing it to be out of focus. on the image this results in what we call depth of field. the larger the aperture the larger the circle of confusion, allowing less to be in focus at a specific focal distance
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#9 deepak srinivasan

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Posted 15 February 2011 - 07:11 AM

Thanks all of you :)
you all really made me understand that its circle of "CONFUSION" :)lol.
After reading a bit of that confusing long articles about "Circle of confusion" i happened to watch a film in a cinema hall last evening and i came to a conclusion of exactly "Circle of confusion" means :)

i attached a picture in that the rounded areas are "Circle of confusion"
am i right ????

"i dint want to get deep into the theory part because it might further confuse me i just wanted to know what is a "Circle of confusion" in a frame thats all :)"

THANKS ALL OF YOU FOR YOUR REPLIES FRIENDS :)
KINDLY SEE THE PICTURE I POSTED :)

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#10 Damien Andre

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Posted 15 February 2011 - 10:58 AM

Thanks all of you :)
you all really made me understand that its circle of "CONFUSION" :)lol.
After reading a bit of that confusing long articles about "Circle of confusion" i happened to watch a film in a cinema hall last evening and i came to a conclusion of exactly "Circle of confusion" means :)

i attached a picture in that the rounded areas are "Circle of confusion"
am i right ????

"i dint want to get deep into the theory part because it might further confuse me i just wanted to know what is a "Circle of confusion" in a frame thats all :)"

THANKS ALL OF YOU FOR YOUR REPLIES FRIENDS :)
KINDLY SEE THE PICTURE I POSTED :)

from how i understand it, those spots are a result of the circle of confusion, but not itself the concept
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#11 Chris Millar

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Posted 15 February 2011 - 04:32 PM

Those spots are called 'bokeh' - they are about as closely related as any visual affect you'll see on film, but not 'circles of confusion'
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#12 K Borowski

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Posted 15 February 2011 - 05:11 PM

WRONG: If you'd understand the concept fully, you'd circle the whole frame and write down fractions of an inch (in the thousandths) or nanometers.


Circle of confusion is EVERYWHERE, not just on the East Coast IATSE test, but eery part of the frame imaged by a lens.
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#13 Chris Millar

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Posted 15 February 2011 - 06:02 PM

You're coming across a bit strong for someone who is learning Karl !

Circle of confusion is EVERYWHERE, not just on the East Coast IATSE test, but every part of the frame imaged by a lens.


Up until the relative point that the CoC is smaller than the mess of randomness induced by other non-optimal lens design factors. I think one of the hindrances in learning about them is that they are best learned 'sideways' to the image plane, looking at a frame you only see one slice of the full picture that is the throw of a lens - and to further fuddle things up a lens is throwing an integration of a bent 3D field of information, where CoC's are dealing with ideal point sources of light, which for all intents and purposes don't exist (forgetting those non-optimal lens design limiting factors myself now!).

Its very hard to communicate this stuff via text - much easier with a pencil and pad and in person


(oh, what's with all the caps in this thread ?)
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#14 Hal Smith

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Posted 15 February 2011 - 08:18 PM

A gathering of Chinese philosphers?

Oh...That's a Circle of Confucians.
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#15 Adrian Sierkowski

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Posted 15 February 2011 - 08:58 PM

ba dum crash ;)
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#16 Chris Millar

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Posted 15 February 2011 - 10:44 PM

da bum crash

Posted Image

Edited by Chris Millar, 15 February 2011 - 10:44 PM.

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#17 Ian Blewitt

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Posted 19 February 2011 - 12:57 AM

Bokeh. The better the lens, the closer they are to a perfect circle. If the lens used is a cheaper lens, you will get hexagons (or any variety of "-gons" also possible... haha)

Though I don't think that's related to circles of confusion at all.
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#18 Chris Millar

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Posted 19 February 2011 - 02:07 AM

Bokeh. The better the lens, the closer they are to a perfect circle. If the lens used is a cheaper lens, you will get hexagons (or any variety of "-gons" also possible... haha)

Though I don't think that's related to circles of confusion at all.


Thats just the shape of the aperture you're talking about - even with a 6 blade iris, you'll get a circle when its fully open ...

Bokeh is more a combination of that shape and then the shape of the profile of light fall off around that edge - there are lots of ways in which it can be fiddled...

A more intriguing example than most:

Posted Image


It might not be related to the technical term 'Circle of Confusion' as used in look up tables and what not but it certainly is related to the underlying concepts and reality of spatial distributions of light.
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