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02-26-2008, 07:04 AM   #31
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QuoteOriginally posted by Gooshin Quote
i'm not talking quality!

i'm asking you how it is CREATED, what within the lens is responsible for bokeh manifestation?
A Technical View of Bokeh by Harold M. Merklinger:

http://www.trenholm.org/hmmerk/ATVB.pdf

02-26-2008, 07:07 AM   #32
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QuoteOriginally posted by Gooshin Quote
i'm not talking quality!

i'm asking you how it is CREATED, what within the lens is responsible for bokeh manifestation?
Oops, we haven't answered that yet? It's the aperture -- which is why almost all pinhole cameras have the same creamy bokeh (unless they're specialty ones with non-round holes). See the Luminous Landscape link above for some REALLY funky bokeh.

[Edit: which is, in fact, a slightly abbreviated version of the Merklinger article Rob posted above.]

Last edited by amateur6; 02-26-2008 at 07:10 AM. Reason: See above.
02-26-2008, 07:11 AM   #33
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thats not the point.. i know that

i was bashed because i said that circle of confusion or how its derived, really, is just another way to look at bokeh and how its created....


its all the same thing we are talking about! :ugh:
02-26-2008, 07:23 AM   #34
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QuoteOriginally posted by Gooshin Quote
thats not the point.. i know that

i was bashed because i said that circle of confusion or how its derived, really, is just another way to look at bokeh and how its created....


its all the same thing we are talking about! :ugh:
The fact is that the CoC refers to a very specific slice of the OOF cone either side of the plane of focus that is used to approximate effective DOF. Bokeh is not just a function of aperture or its shape, it's those factors combined with the optical characteristics of the lens design, subject distance and the proximity of visible objects either side of the focus distance. So it's not the same.

02-26-2008, 07:24 AM   #35
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QuoteOriginally posted by distudio Quote
The fact is that the CoC refers to a very specific slice of the OOF cone either side of the plane of focus. Bokeh is not just a function of aperture it's that combined with the optical characteristics of the lens design, subject distance and the proximity of visible objects either side of the focus distance.
but if all we are talking about is a size comparizon in what (we assumed) to be identical lenses....

the point is, all roads lead to Rome.
02-26-2008, 07:27 AM   #36
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QuoteOriginally posted by Gooshin Quote
but if all we are talking about is a size comparizon in what (we assumed) to be identical lenses....

the point is, all roads lead to Rome.

LOL, now you're confusing me. ;-)
02-26-2008, 07:31 AM   #37
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QuoteOriginally posted by distudio Quote
LOL, now you're confusing me. ;-)

this is from the first post...

"A question for you optical experts out there. Will the circle of confusion (appearing in the rendering of out-of-focus areas) for a DA lens be the same size as that of an FF lens of the same focal length, focus distance, and all other variables being equal?"
02-26-2008, 07:52 AM   #38
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QuoteOriginally posted by Gooshin Quote
this is from the first post...

"A question for you optical experts out there. Will the circle of confusion (appearing in the rendering of out-of-focus areas) for a DA lens be the same size as that of an FF lens of the same focal length, focus distance, and all other variables being equal?"
Well it's obvious reading through the thread that the answer is a definite yes and no (it depends which variables you care to ignore because they aren't equal with differing formats).

Ultimately your question ignores the commonly acknowledged definitiuon for CoC:

Circle of confusion - Wikipedia, the free encyclopedia

Hence the circle of confusion that the thread has produced.

Cheers,

02-26-2008, 08:04 AM   #39
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QuoteOriginally posted by distudio Quote
Well it's obvious reading through the thread that the answer is a definite yes and no (it depends which variables you care to ignore because they aren't equal with differing formats).

Ultimately your question ignores the commonly acknowledged definitiuon for CoC:

Circle of confusion - Wikipedia, the free encyclopedia

Hence the circle of confusion that the thread has produced.

Cheers,
its not my question, its his question, and no one is confused but you, since instead of answering the question you decided to discuss semantics.
02-26-2008, 09:18 AM   #40
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Bokeh Article--Long Version

Has anyone seen the "long version" of the original Merklinger article from Photo Techniques? My original copy didn't survive a move a few years ago and I'm interested in reconnecting with this piece. The long version I'm referring to included photos of hub caps and tree branches to show the "double vision" effect--as I recall--Merklinger didn't use the term "double vision", that's my nontechnical memory at work. The abridged version with photos of the figurines has been posted in this forum several times, but I've yet to see the version I remember from the original magazine. It also seems to me that the original article delved into some of the "side issues" affecting bokeh that may resolve some of the coc and bokeh ideas being discussed in this forum...
02-26-2008, 01:59 PM   #41
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QuoteOriginally posted by Gooshin Quote
its not my question, its his question, and no one is confused but you, since instead of answering the question you decided to discuss semantics.
My apologies, I did mistake the origin of the question, but in this case the semantics are important, there's no point perpetuating ignorance.
02-26-2008, 05:49 PM   #42
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QuoteOriginally posted by d.bradley Quote
I ask because of this discussion:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/21500-comparis...8-200-4-a.html

and this image linked in that post:

I still cannot understand all the fuzz about.

Obviously, circle of confusion diameters are proportional to aperture which is defined to be f/x.

So, if a, b are the sizes of confusion circles at at f/4 and f/5.6, respectively, one gets

b = a *4/5.6 = 0.714 a

Taking the measure, the DA is fine whereas A has wrong aperture f/4.7, not f/5.6!

Why this is so, we can only speculate.... (I guess it is an AF error).


And of course, the size of the circle of confusion only depends on focal length, aperture, and distances to in-focus and out-of-focus subjects.

Bokeh, as it is used now in English and German language, seems to mean the rendition quality at a given size of circle of confusion, which is primarily determined by out-of-focus CA and shape/number of aperture blades.
02-26-2008, 07:43 PM   #43
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QuoteOriginally posted by falconeye Quote
So, if a, b are the sizes of confusion circles at at f/4 and f/5.6, respectively, one gets

b = a *4/5.6 = 0.714 a

Taking the measure, the DA is fine whereas A has wrong aperture f/4.7, not f/5.6!
F/5.6 is an approximation, it is closer to f/5.66 in reality. [ √2 * 4.0 ]

The F/4.7 measured could just mean some sticky aperture blades on the subject lens. I.e. not stopping down fast enough before the exposure is made.
02-26-2008, 07:46 PM   #44
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QuoteOriginally posted by Rickster Quote
F/5.6 is an approximation, it is closer to f/5.66 in reality. [ √2 * 4.0 ]

The F/4.7 measured could just mean some sticky aperture blades on the subject lens. I.e. not stopping down fast enough before the exposure is made.
which is probably the most logical conclusion, and one most unnerving.

would mirror lockup avoid such a situation if one was to use older lenses?
02-26-2008, 09:06 PM   #45
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QuoteOriginally posted by distudio Quote
in this case the semantics are important, there's no point perpetuating ignorance.
It seems like a losing battle to be fighting at this point though, doesn't it?

It seems many people are using the term "Circle of Confusion" to refer to "the diameter of an out of focus point source." Coc is properly described by that diameter, but the terms are in no way interchangeable. Circle of confusion is the largest possible diameter of that same out of focus point source that will still be viewed as acceptable focus when determining theoretical depth of field using depth of field calculators and the like. That diameter is usually quite small, and certainly much smaller than the samples we've been looking at.

I don't think anyone's harping on semantics here to be mean-spirited or to demonstrate superior knowledge in a bossy, know-it-all sort of way. These discussions bog down and become confusing (as we've demonstrated) when terms are misused, so it is better for everyone if they aren't. That's all.

Will
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