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02-25-2008, 11:04 AM   #16
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QuoteOriginally posted by Gooshin Quote
but a lens with an aperture ring that clicks into pre-defined (and extensively tested) aperture positions would have much more credibility than a fully electronically controlled lens.
Yes, I agree.

02-25-2008, 11:27 AM   #17
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Here is a more complete row.
Quite noisy, because it is already quite dark.



Larger copy:
http://www.informatik.uni-bremen.de/foto-ag/Bilder/Vergleich-2.jpg
02-25-2008, 12:01 PM   #18
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cool!

definetly a difference in sizing after F4, almost like the FA is "in the middle" between the DA lines,

perhaps this is due to the 8 blades vs 9 blades?
02-25-2008, 05:26 PM   #19
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QuoteOriginally posted by Gooshin Quote
no, circle of confusion is bokeh...
Sorry, but it isn't. From the same site I linked to too:

"In photography, the circle of confusion diameter limit (“CoC”) is sometimes defined as the largest blur circle that will still be perceived by the human eye as a point when viewed at a distance of 25 cm (and variations thereon)."

When was the last time you heard of someone enthusing over the pointyness of their lens' bokeh? (Well, actually, it happens all the time, except it's called "resolution" in those arguments) Bokeh and CoC are opposites: one is when the projected point of light still appears as a point of light, and the other is when the point of light doesn't appear as a point of light at all.

02-25-2008, 05:40 PM   #20
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QuoteOriginally posted by Jerry Thirsty Quote
Sorry, but it isn't. From the same site I linked to too:

"In photography, the circle of confusion diameter limit (“CoC”) is sometimes defined as the largest blur circle that will still be perceived by the human eye as a point when viewed at a distance of 25 cm (and variations thereon)."

When was the last time you heard of someone enthusing over the pointyness of their lens' bokeh? (Well, actually, it happens all the time, except it's called "resolution" in those arguments) Bokeh and CoC are opposites: one is when the projected point of light still appears as a point of light, and the other is when the point of light doesn't appear as a point of light at all.
Exactly, CoC is only used to determine theoretical DOF. CoC is generally accepted to change with capture format for the same lens since the magnification required to produce the same print size will differ. Bokeh is the Japanese name for the perceived quality of out of focus areas of the image.
02-25-2008, 06:04 PM   #21
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okay.. how does bokeh manifest itself, in technical terms?
02-25-2008, 07:01 PM   #22
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QuoteOriginally posted by Gooshin Quote
okay.. how does bokeh manifest itself, in technical terms?
It's a perceived quality, it's not technically defined so no one has produced an objective method of assessment. Good bokeh to one artist maybe bad bokeh to another.

Last edited by distudio; 02-25-2008 at 10:16 PM.
02-25-2008, 10:12 PM   #23
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The circle size should change by the factor (√2)/2 = .707 per full stop.

02-25-2008, 10:25 PM   #24
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QuoteOriginally posted by distudio Quote
It's a perceived quality, it's not technically defined so no one has produced an objective method of assessment. Good bokeh to one artist maybe bad bokeh to another.
But, there are a few objective factors: generally, neutral disks are regarded as more pleasing than dots with bright centers, which are in turn nicer than donut shapes or bright-edged circles.
02-25-2008, 10:43 PM   #25
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QuoteOriginally posted by mattdm Quote
But, there are a few objective factors: generally, neutral disks are regarded as more pleasing than dots with bright centers, which are in turn nicer than donut shapes or bright-edged circles.
The point is that it depends who the viewer is as to what they deem as nicer.
02-26-2008, 12:40 AM   #26
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QuoteOriginally posted by Gooshin Quote
definetly a difference in sizing after F4, almost like the A is "in the middle" between the DA lines,
perhaps this is due to the 8 blades vs 9 blades?
I have two ideas what the cause may be,
  • it could have to do with the internal focussing of the DA*. If the focal length is only 180-190mm instead of 200mm, the circles will be smaller. The distance was about 3m, so this could be possible.
  • I have the suspicion, not sure though, that the size of the circle is also dependent of the position of the aperture within the lens.
Anybody knows more about this?
02-26-2008, 04:10 AM   #27
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QuoteOriginally posted by distudio Quote
Exactly, CoC is only used to determine theoretical DOF. CoC is generally accepted to change with capture format for the same lens since the magnification required to produce the same print size will differ. Bokeh is the Japanese name for the perceived quality of out of focus areas of the image.
You've nailed it as far as I'm concerned, but I'd add that...

1.) Circle of confusion is also generally accepted to change with presentation size and format as well. The Coc used to determine DoF for a 50" print will be very different from the Coc used to determine DoF for a web image. You basically said as much ("required to produce the same print size"), but I figured it was worth clarifying.

2.) Coc will change from lens to lens, even if it doesn't seem like it should. Quality of optics, aperture blades, and a number of other factors will create a difference.

3. That point sources will bloom into larger circles when out of focus to produce bokeh is related to circle of confusion, and the whole subject is pretty difficult to grasp if you aren't accustomed to thinking about optical science.

4. I'm getting the feeling that the original poster was actually asking about bokeh, not CoC.

Will
02-26-2008, 04:20 AM   #28
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...and on the subject of bokeh, judging from the test shots here, bokeh is most pleasing (to me) and most round wide open. The aperture shape becomes visible once the lens is stopped down at all, and thus at f/4 the FA looks nicer... it is wide open. 8 blades or not, wide open it looks better than the 9 blades of the DA. At 5.6, to me, the nine-bladed aperture becomes superior, which I would expect it to continue to do. How the lens holds up to diffraction, however, could change that I suppose.

I typically prefer as many blades as possible, so I was glad to see this test (I've never done one) showing that "feature" of using a slower lens wide open.

I'm remembering some old Zeiss primes I used to use when shooting 16mm motion picture film that had three-bladed irises, and man was that some nasty looking bokeh.

Will
02-26-2008, 04:54 AM   #29
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QuoteOriginally posted by wiyum Quote

4. I'm getting the feeling that the original poster was actually asking about bokeh, not CoC.
Not only that, I'm guessing the OP is sorry they asked!

A few links for anyone who wants to do further reading in a more authoritative source than Wikipedia (from shortest to longest... funny how their page titles are the inverse of their actual length):

Circle of Confusion: Optical: Glossary: Learn: Digital Photography Review <-- DP Review

Understanding Depth of Field in Photography <-- Cambridge in Colour

Digital Depth of Field <-- Bob Atkins

bokeh <-- Luminous Landscape (the article, despite the title, uses the unfortunate "boke" transliteration of "bokeh")
02-26-2008, 06:35 AM   #30
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QuoteOriginally posted by distudio Quote
It's a perceived quality, it's not technically defined so no one has produced an objective method of assessment. Good bokeh to one artist maybe bad bokeh to another.
i'm not talking quality!

i'm asking you how it is CREATED, what within the lens is responsible for bokeh manifestation?
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