Help settle an argument: bokeh/COF

[pbryant]

Hi all,

I'm hoping the pros on these boards can help settle a friendly *ahem* debate 'twixt myself and another photographer.

The disagreement centers on the proper term for the bright spots that appear in a shot with pronounced, high contrast bokeh (for example a dusk scene where the subject is on a balcony with city lights in the background).

I come from a more traditional background, and am comfortable (happy, even) with the calculations for DOF, acceptable COC, and the like. To me then, the term "circle of confusion" means one thing (as relates to photography): the diameter of the largest acceptable blur circle, when viewing an image under normal circumstances. Nitpick as necessary, but it gets the point across.

To my partner, "circle of confusion" is a term to describe the "halos" that appear around the lights in the scenario mentioned above.

See: http://weheartit.com/images/thumbs/20080427231748.jpg

So who's right? To me it's a clear misappropriation of optical nomenclature, but I'm certainly open to correction from the experts here. But we need an answer, before someone gets bonked with the 200 f/4.

Thanks so much!
Paul

 

[Moglex]

Check Here.

Should tell you all you need to know.

 

[pbryant]

Thanks Moglex,

I'm familiar with that article, and have actually used it as evidence in our ongoing discussion.

I was looking more for a consensus as to whether the term has become a colloquialism for the aforementioned "halos."

edit: do they even -have- a name? What do you call them?

Thanks again,
Paul

 

[Helen B]

The circle of confusion is simply the image of an object point, whether the image is in the plane of best focus or not. It only applies to depth of field calculations when it is given a limit. Your definition of CoC is really the definition of maximum acceptable CoC.

Best,
Helen

 

[Bifurcator]

...the aforementioned "halos."

do they even -have- a name? What do you call them?

Blurred lights.

 

[pbryant]

Ha... Helen, Bifurcator, hanks for your help, and for the laugh.

Helen, I've been reading the forum for a long time, and have seen you involved some pretty technically intense discussions... I appreciate you weighing in.

Cheers all! Time to crash.
P.

 

[Sark]

The circle of confusion is simply the image of an object point, whether the image is in the plane of best focus or not. It only applies to depth of field calculations when it is given a limit. Your definition of CoC is really the definition of maximum acceptable CoC.

Best,
Helen

I was always lead to believe a circle that fell within the 0.2mm limit in print was the "largest permissable/acceptable circle of confusion", and a circle that fell outside the 0.2mm limit was simply a "circle of confusion". There is certainly evidence to support this if you google. Not that that is always entirely relevent, or accurate.

Sark

 

[Helen B]

Any image of an object point that is not itself a point can be called a circle of confusion - it doesn't matter whether it is inside a limit or outside it. The limit that is used for a DoF or other sharpness quality criterion does not have to be 0.2 mm on a print, it can be whatever is appropriate for the application.

As well as the special case of the maximum acceptable CoC, there is also the special case of the least circle of confusion - the smallest 'circle' (they are rarely truly circular) that a lens can produce in the plane of best focus.

As an aside, one of my favourite books is Hollis Frampton's Circles of Confusion - though it isn't about geometric optics. How many greens are there in grass? Far more important.

Best,
Helen

 

[AndrewG]

...and who the hell came up with 'bokeh'? What a horrible word; I understand it's Japanese but is this a recent affectation; it certainly wasn't in use a few years ago.