CoC for EOS 20D w/ ef17-40L

[mike_digital]

to all the tech-guru's out there:

does anyone know the "Circle of Confusion" for the 20D ??
(or generally, a list for all Canon DSLR's ?)

a literature and internet search gave me various results:

some say an APS format chip like 10/20D has a CoC of 0.019mm.....
some say an analog APS cam has 0.025mm
some say that canon ef-lenses have a CoC of 0.035mm regardless of the sensor format....

so what's the truth ??

cheers mike

[Perfect_10]

dunno .. I'm now totally confused :lol: :lol:

[Andy_T]

Hmm ... if you want to be thoroughly confused, refer to this thread :lol:
http://photography-on-the.net/forum/showthread.php?t=2849&postdays=0&postorder=asc&sta rt=180

Or, directly proceed to the spreadsheet with the calculation for a lot of other cameras. You should be able to calculate the values for the 20D:

http://home.globalcrossing.net/~zilch0/tools/DigiSpecs.xls

Best regards,
Andy

[EXA1a]

to all the tech-guru's out there:

does anyone know the "Circle of Confusion" for the 20D ??
(or generally, a list for all Canon DSLR's ?)

a literature and internet search gave me various results:

some say an APS format chip like 10/20D has a CoC of 0.019mm.....
some say an analog APS cam has 0.025mm
some say that canon ef-lenses have a CoC of 0.035mm regardless of the sensor format....

so what's the truth ??

cheers mike
There is no truth. CoC depends of the viewing distance and your eye sight.
1. Generally, people use identical numbers for the diagonal of the viewed picture and the viewing distance, e.g. distance dis=200mm and diagonal dia=200mm
2. Generally, people use an average eye resolving power res=1/1400 of the viewing distance (e.g. you can resolve two points with a distance of 1/1400m=0.71mm from a distance of 1m)
3. Diagonal of a 1.6x sensor diaS=27mm

The formula:
CoC=res x diaS x dis/dia
The calculation:
CoC=1/1400 x 27mm=0.019mm

With a good eye sight, e.g. 1/2000 of the viewing distance, you get
CoC=1/2000 x 27mm=0.0135mm.
With a bad eye sight, e.g. 1/1000 of the viewing distance, you get
CoC=1/1000 x 27mm=0.027mm

--Jens--

[mike_digital]

WOW ! loads to read !

but here are some citations of infos i found:

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from:http://www.luminous-landscape.com/tutorials/understanding-series/dof.shtml

".......when establishing their depth of field tables and lens markings.
Canon, for example, confirms in their book EF Lens Work II, that they
use 0.035mm as their COF for all modern EF model lenses."

-----------------------------------------------------------------------------------

from:http://www.dofmaster.com/digital_coc.html

"The circles of confusion above were calculated using the formula:

CoC = (CoC for 35mm format) / (Digital camera lens focal length multiplier)

The focal length multiplier for a camera is specified by the manufacturer,
or is calculated using the formula:

Multiplier = (35mm equivalent lens focal length) / (Actual lens focal length)"

also scroll down to the Circle of Confusion Calculator !

-----------------------------------------------------------------------------------

so, i assume that if 17mm x 1.6 = ~27mm and Canon's 35mm format
circle of confusion is in fact 0.035mm than the closest guess to the "REAL"
CoC for the 20D w/ ef-lens is 0.022mm

???? what do you think ????

[EXA1a]

so, i assume that if 17mm x 1.6 = ~27mm and Canon's 35mm format
circle of confusion is in fact 0.035mm than the closest guess to the "REAL"
CoC for the 20D w/ ef-lens is 0.022mm

???? what do you think ????
As I pointed out, there is in fact not such a thing as a "real" CoC.

And, more importantly, LENSES don't have CoCs at all. But you need a certain CoC, which is sensor size-dependent, to create the DOF markings on the lens. This shows that the DOF markings of the EF lenses are not accurate anymore for 1.6x sensors.

--Jens--

[mike_digital]

all righty than !
--> the dof-markings on lenses aren't right !
or let's say the rest of them ;-)
thats one reason why most new lenses don't have markings anymore....


As I pointed out, there is in fact not such a thing as a "real" CoC.

yes i know about the only weak factor in that game: guess.....its the human eye.

but for printing out such "hyperfocal charts" like in my post above, you have to set a CoC ! ?!?
--> a lovely tool in the field for achieving best dof possible. especially for the landscape photographer.

guess i have to try different settings for different resolutions AKA printsize. ;-(

tschü,

mike
[/quote]

[hmhm]

The CoC is a quantitative expression of "how blurry is too blurry", or if you prefer, "how sharp is just barely sharp enough?"

Your requirements for "good enough" depend on how big you plan to print, from what distance you plan to view the prints, and your own subjective notion of "sharp enough".

The easy part of the question is to answer how CoC varies from one format to another, and that's "linearly, with format size". So a 20D with a CoC that's 1/1.6 the CoC used on a 35mm film camera would be considered "equivalent".

It you haven't got a clue where to start, you could do worse than to assume a 35mm film CoC of .025 and a corresponding 1.6x DSLR CoC of .017 . This really isn't an exact science, though, of course.
-harry

[Belmondo]

This is an interesting topic

I feel obliged to point out that nearly everyone in my circle is confused, especially on this subject.