Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-26-2009, 03:44 AM   #16
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by spinmar Quote
CoC for k20D is different.....
For optimum quality, I always calculate with a circle of (least) confusion of 0.01mm. That does account for the fact, that the pixels are not seamlessly placed on the sensor, but that there are non-photosensitive bridges between them. Though there are few lenses, that are able to match that really strong criterion.

Ben

02-26-2009, 10:36 AM   #17
Veteran Member




Join Date: Sep 2007
Location: USA
Posts: 1,812
QuoteOriginally posted by spinmar Quote
CoC for k20D is different.....
I am not too sure about that.

Obviously the sensor pixel site size is different -
but the Circle of Confusion in photography (Wikipedia link) is not necessarily about pixel size -

QUOTE from Wikipedia -
" 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). With this definition, the CoC in the original image depends on three factors:
  1. Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2000, 52), is approximately 25 cm. At this distance , a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.
  2. Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. A comfortable viewing distance is also one at which the angle of view is approximately 60 (Ray 2000, 52); at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8″10″ image. It often may be reasonable to assume that, for whole-image viewing, an image larger than 8″10″ will be viewed at a distance greater than 25 cm, for which a larger CoC may be acceptable.
  3. Enlargement from the original image (the focal plane image on the film or image sensor) to the final image (print, usually). If an 810 original image is contact printed, there is no enlargement, and the CoC for the original image is the same as that in the final image. However, if the long dimension of a 35 mm image is enlarged to approximately 25 cm (10 inches), the enlargement is approximately 7, and the CoC for the original image is 0.2 mm / 7, or 0.029 mm.
All three factors are accommodated with this formula:
CoC Diameter Limit (mm) = anticipated viewing distance (cm) / desired print resolution (lp/mm) for a 25 cm viewing distance / anticipated enlargement factor / 25 For example, to support a print resolution equivalent to 5 lp/mm for a 25 cm viewing distance when the anticipated viewing distance is 50 cm and the anticipated enlargement factor is 8:
CoC Diameter Limit = 50 / 5 / 8 / 25 = 0.05 mm Since the final image size is not usually known at the time of taking a photograph, it is common to assume a standard size such as 25 cm width, along with a conventional final-image CoC of 0.2 mm, which is 1/1250 of the image width. Conventions in terms of the diagonal measure are also commonly used. The DoF computed using these conventions will need to be adjusted if the original image is cropped before enlarging to the final image size, or if the size and viewing assumptions are altered.
Using the so-called “Zeiss formula” the circle of confusion is sometimes calculated as d/1730 where d is the diagonal measure of the original image (the camera format). For full-frame 35 mm format (24 mm 36 mm, 43 mm diagonal) this comes out to be 0.024 mm. A more widely used CoC is d/1500, or 0.029 mm for full-frame 35 mm format, which corresponds to resolving 5 lines per millimeter on a print of 30 cm diagonal. Values of 0.030 mm and 0.033 mm are also common for full-frame 35 mm format. For practical purposes, d/1730, a final-image CoC of 0.2 mm, and d/1500 give very similar results. "


Crop taken from Wikipedia -


Notice they provide CoC for most common sensor sizes - regardless of pixel count/density.
02-26-2009, 01:38 PM   #18
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by UnknownVT Quote
I am not too sure about that.

Obviously the sensor pixel site size is different -
but the Circle of Confusion in photography (Wikipedia link) is not necessarily about pixel size -

QUOTE from Wikipedia -
" 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). With this definition, the CoC in the original image depends on three factors:
[LIST=1][*]Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2000, 52), is approximately 25 cm. At this distance , a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.....
It seems to me there are two reasonable definitions regarding DOF's Circle of Confusion. The one described in your discussion is about the largest CoC needed to see a certain depth resolution on a print or display. This display CoC is referred back to the sensor; it is reduced in size by whatever the appropriate demagnification is appropriate for the overall sensor & display dimensions. For a constant display specification this implies a CoC inversely proportional to sensor dimension.

The CoC above is what the display requires; it does not consider the sensor's actual capabilities. The smallest possible CoC on the other hand is fixed by the physical characteristics of the sensor regardless of the display's needs. Pixel spacing clearly provides a lower limit to sensor CoC; actual limits are larger than this theoretical limit due to anti-aliasing filters, etc.

The existence of two reasonable limits to CoC causes much difficulty in discussions like this.

Dave
02-26-2009, 01:49 PM   #19
Veteran Member




Join Date: Sep 2007
Location: USA
Posts: 1,812
QuoteOriginally posted by newarts Quote
The existence of two reasonable limits to CoC causes much difficulty in discussions like this.
Sorry it isn't.
There is a definition for CoC -
and that is what's being used for the HyperFocal distance and DoF.

Pixel size/pitch is not relevant, other than not having enough pixels for the enlargement.

Otherwise Hyperfocal distance (and DoF) would have been computed for the grain size in film (being the equivalent resolution limit) - and it isn't, it is the CoC - which is the limit of "resolution" that the eye can see -
pixel size doesn't come into it - other than the limit to which one can enlarge the image without image breakdown.

02-26-2009, 02:09 PM   #20
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by UnknownVT Quote
Sorry it isn't.....

Pixel size/pitch is not relevant, other than not having enough pixels for the enlargement....

.... - other than the limit to which one can enlarge the image without image breakdown.
Which is exactly what I said. Without such qualification it is not possible to say how large a print can be made (or how far the data from a sensor can be cropped) to meet a given viewing criterion.

I repeat; sensor characteristics fix the lower limit of CoC.

Your quote from Wikipedia seems to include this notion.
QuoteQuote:
The DoF computed using these conventions will need to be adjusted if the original image is cropped before enlarging to the final image size, or if the size and viewing assumptions are altered.
Dave

Last edited by newarts; 02-26-2009 at 02:18 PM.
02-26-2009, 03:38 PM   #21
Veteran Member




Join Date: Sep 2007
Location: USA
Posts: 1,812
QuoteOriginally posted by newarts Quote
Which is exactly what I said. Without such qualification it is not possible to say how large a print can be made (or how far the data from a sensor can be cropped) to meet a given viewing criterion.
I repeat; sensor characteristics fix the lower limit of CoC.
I think we are talking cross purposes.

The quote from Wikipedia is about the magnitude of the enlargement - ie: if cropped and printed to say 10x8 - it is not the same magnification as a 10x8 enlargement from a full frame - pretty obvious.

The reference to the viewing distance is mainly for larger prints when viewing at closer than the "normal" distance - then the viewing is more critical, so the CoC criteria changes.

Of course the final print size determines the CoC used in the calculation - but that is INDEPENDENT of the number of pixels - other than the limit to which an image can be enlarged.

Please read how DoF and Hyperfocal distance are calculated.

Please read the entire CoC Wikipedia entry and see if pixels are even mentioned for the determination of CoC.

The CoC used is the limit that the eye can resolve on the print/image size (at what is a "normal" viewing distance) - and scaled to the actual "CoC" on the sensor - so if the CoC is smaller than the pixel size - then we are at the image limit - that is exactly the same as I have been saying that the pixel size is only relevant when it is the limit if there is a breakdown of the image due to the lack of pixels.

Film was used in photography long before digital chips - the hyperfocal distance, DoF and CoC were deterimed without any regard to grain size or resolution of the film or film/lens combination for centuries and taught as such in academia - digital photography is NO different - other than using a sensor chip instead of film to record the image.
02-26-2009, 03:58 PM   #22
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by UnknownVT Quote
I think we are talking cross purposes.

The quote from Wikipedia is about the magnitude of the enlargement - ie: if cropped and printed to say 10x8 - it is not the same magnification as a 10x8 enlargement from a full frame - pretty obvious.

The reference to the viewing distance is mainly for larger prints when viewing at closer than the "normal" distance - then the viewing is more critical, so the CoC criteria changes.

Of course the final print size determines the CoC used in the calculation - but that is INDEPENDENT of the number of pixels - other than the limit to which an image can be enlarged.

Please read how DoF and Hyperfocal distance are calculated.

Please read the entire CoC Wikipedia entry and see if pixels are even mentioned for the determination of CoC.

The CoC used is the limit that the eye can resolve on the print/image size (at what is a "normal" viewing distance) - and scaled to the actual "CoC" on the sensor - so if the CoC is smaller than the pixel size - then we are at the image limit - that is exactly the same as I have been saying that the pixel size is only relevant when it is the limit if there is a breakdown of the image due to the lack of pixels.

Film was used in photography long before digital chips - the hyperfocal distance, DoF and CoC were deterimed without any regard to grain size or resolution of the film or film/lens combination for centuries and taught as such in academia - digital photography is NO different - other than using a sensor chip instead of film to record the image.

Wikipedia has sometimes nicely informed articles, sometimes not. It is not the holy grail of knowledge. The circle of (least) confusion as used for film is a measure which was made with respect to that medium. It needs adaption to a new medium, namely digital sensors, simply because they work very differently from film. We are not longer dealing with a random distribution of image forming silver halides or dye clouds, but with a static rectangular matrix of pixels, which on top have non-image forming intermediate structures between them. So it makes sense to include the pixels and their size into the definition for the circle of confusion.

The circle of confusion - I think, I should emphasize that - is not a law of physics, but simply an applied measure. The laws of physics, that are relevant for our issue, define the size of the airy disc - not that of the circle of confusion. So we are free, to find a new definition, which can be applied adequately to the digital pixel matrix we call a sensor.

Taking pixel sizes of app. 6 - 9 nm into account and leaving some space around them for the supporting structures (read-out pipes, gates etc.), using a desirable circle of confusion of 0.01nm seems very sensible to me. I have been discussing this issue long and wide in other forums as well with physicists and photogs alike and found so far no reason, why this would not be a sensible measure - quite to the contrary. And to my knowledge, this desirable 0.01 nm circle of confusion is also supported by quite a few other people in the industry.

Ben
02-26-2009, 04:09 PM   #23
Veteran Member




Join Date: Sep 2007
Location: USA
Posts: 1,812
QuoteOriginally posted by Ben_Edict Quote
Wikipedia has sometimes nicely informed articles, sometimes not. It is not the holy grail of knowledge.
I merely used Wikipedia as a convenient reference - please then refer to any Physics text book or photographic book on CoC.


QuoteOriginally posted by Ben_Edict Quote
Taking pixel sizes of app. 6 - 9 nm into account and leaving some space around them for the supporting structures (read-out pipes, gates etc.), using a desirable circle of confusion of 0.01nm seems very sensible to me. I have been discussing this issue long and wide in other forums as well with physicists and photogs alike and found so far no reason, why this would not be a sensible measure - quite to the contrary. And to my knowledge, this desirable 0.01 nm circle of confusion is also supported by quite a few other people in the industry.
Really - please provide references - the common CoC used for 35mm film is 0.029mm and for an APS-C sensor is 0.018mm -

The "0.01 nm" CoC you gave - that's nano metres (10 to the power of -9) right? -
that is a magnitude of 1/1,000,000th when compared to mm - milli-metres!
Are you sure?

02-27-2009, 03:47 AM   #24
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by UnknownVT Quote
I merely used Wikipedia as a convenient reference - please then refer to any Physics text book or photographic book on CoC.




Really - please provide references - the common CoC used for 35mm film is 0.029mm and for an APS-C sensor is 0.018mm -

The "0.01 nm" CoC you gave - that's nano metres (10 to the power of -9) right? -
that is a magnitude of 1/1,000,000th when compared to mm - milli-metres!
Are you sure?
Sorry, for the typo. I am used to use nm so I simply typed it instead of mm - maybe just because I used nm before for the pixel size...

Ben
02-27-2009, 04:01 AM   #25
Veteran Member
Ben_Edict's Avatar

Join Date: Jul 2007
Location: SouthWest "Regio"
Photos: Albums
Posts: 3,303
QuoteOriginally posted by UnknownVT Quote
Really - please provide references - the common CoC used for 35mm film is 0.029mm and for an APS-C sensor is 0.018mm -
I don't care too much about what is given for APS-C sensors, as usually these definitions are based on a simplistic assumption: they divide the sensor sizes through the pixel count.

But this is only half the story, as it simply overlooks, that the pixels are smaller, than this simple division would give as a result. I apply a factor 2 smaller desirable circle of confusion, because the single pixel is much smaller and it is very desirably to keep the size of a point source basically within one pixel. This is a much harder measure than was necessary with film, as the rectangular matrix of the sensor make a point source, spread above several pixels much more visible, because it necessarily is spread over 4 pixels, if it is larger than 1 pixel.

As I wrote above: the circle of least confusion is not a physical constant, but a simple definition, based on experience and aimed at a certain application (enlargement). Whether I apply a harder definition or not must not concern you. You can use whatever satisfies your needs and expectation. And I use, what I find acceptable for my needs.

regards
Ben
02-27-2009, 04:05 AM   #26
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteQuote:
Please read how DoF and Hyperfocal distance are calculated.
No need, I am quite familiar with the underlying models.

QuoteQuote:
Please read the entire CoC Wikipedia entry and see if pixels are even mentioned for the determination of CoC.
I take your word, but that does not mean the Wiki is complete.

QuoteQuote:
....- so if the CoC is smaller than the pixel size - then we are at the image limit - that is exactly the same as I have been saying that the pixel size is only relevant when it is the limit if there is a breakdown of the image due to the lack of pixels.....
We are in complete agreement. What you have described as the "image limit" is by your description the lower limit to the CoC "if the CoC is smaller than the pixel size - then we are at the image limit"; the CoC at this lower limit is independent of the display system.

Dave
02-27-2009, 11:17 AM   #27
Veteran Member




Join Date: Sep 2007
Location: USA
Posts: 1,812
QuoteOriginally posted by newarts Quote
We are in complete agreement. What you have described as the "image limit" is by your description the lower limit to the CoC "if the CoC is smaller than the pixel size - then we are at the image limit"; the CoC at this lower limit is independent of the display system.
Thanks, I do not mean to prolong this -

If you'll allow me to go back to basic fundamentals for a moment -

CoC is more about human physiology than it is about technology (sensors or pixel count).

The way the CoC is derived is by figuring out what the eye can resolve - this is the actual CoC on print.

Then it is simply figuring out the amount of magnification required to get that print size. eg: for simplicity let's say it's a 10x enlargement - then the CoC on the original image (be it on film or sensor) has to be 1/10 the size that the eye can just resolve on print.

That's it - nothing to do with pixel size, count or film grain resolution limit etc.
02-27-2009, 02:21 PM   #28
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by UnknownVT Quote
Thanks, I do not mean to prolong this -

If you'll allow me to go back to basic fundamentals for a moment -

CoC is more about human physiology than it is about technology (sensors or pixel count)....

That's it - nothing to do with pixel size, count or film grain resolution limit etc.

Yes, that's the starting point for one way to describe the geometric optics relating to depth of field, but it doesn't complete the story.

Once the CoC term is put into the equations, one must state the qualification that there is a lower limit to it that defines the domain of validity for the relationship. Without such qualification the relationships imply there is no enlargement limit for a camera system.

Your own language says there is a lower limit to CoC that occurs when there is insufficient sensor pixel density.

But I suppose this argument is more about purity of terminology origins vs utility of geometric optics & descriptive mathematics applied thereto.

In fairness, it should be pointed out that the limits to depth of field are most likely better described by near field equations & "Depth of Focus" concepts. It turns out the geometric optics description of the focal point of an image being the intersection of two straight lines is incorrect. The actual image of an in-focus point is roughly an ellipsoid elongated in the direction of the optic axis.

Here's a figure from Olympus showing the shape of an "in-focus" point; The left image is for standard optics; the optic axis is vertical: (PSF is "Point Spread Function" - the image of an infinitesimal point in space)



Notice that the length of the focal disk along the optic axis is a few times its diameter.
This length is purely a function of near field interaction of light waves at a focal plane and has nothing to do with human perception of a print nor pixels on a sensor; it determines the obtainable resolution of a lens based image in the depth direction.

Dave

PS in real life I think one runs into the pixel spacing limit to image resolution (in x, y, and z directions) before the diffraction based limits shown above (but I'm not certain of the details.)

Last edited by newarts; 02-27-2009 at 02:31 PM.
02-27-2009, 02:37 PM   #29
Veteran Member




Join Date: Sep 2007
Location: USA
Posts: 1,812
QuoteOriginally posted by newarts Quote
Notice that the length of the focal disk along the optic axis is a few times its diameter.
This length is purely a function of near field interaction of light waves at a focal plane and has nothing to do with human perception of a print nor pixels on a sensor; it determines the obtainable resolution of a lens based image in the depth direction.
Dave we're at cross-purposes again.

CoC is about what we can see and therefore what we will find acceptable "in focus" for any DoF or hyperfocal distance -

What you've shown is the non-linearity of an actual imaging system.

There is nothing that relates the two -
I do acknowledge less than ideal/non-linear (ie: faulty) and limits to an imaging system may limit any derivation
- but this is hardly what we were looking at -
let's just take the really silly example of a single pixel sensor - it would be absolutely nonsesensical to try to calculate the CoC for DoF or hyperfocal distance for that sensor since one cannot really capture any photographic image as we understand it.

However getting back on topic -
to calculate the hyperfocal distance for practical usage -
one uses the CoC for the sensor dimensions - and that simply is using human physiology - ie: the eye's limit of resolution - by definition - assuming an adequate imaging system (ie: enough pixels to produce an acceptable image in the first place)
- so in practice the CoC is not dependent on the pixel size or whether they are circular or not.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, distance, dof, dslr, focus, length, meters, photography, scale
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
What focal length for a manual zoom? janstew Pentax SLR Lens Discussion 24 01-09-2011 08:26 AM
How Can You Easily Tell How far a Given Focal Length will Zoom? jaieger Troubleshooting and Beginner Help 20 07-18-2010 09:47 AM
focus with zoom, then change focal length? WMBP Pentax DSLR Discussion 21 08-08-2009 10:25 AM
Best Mid Length Zoom ? seacapt Pentax SLR Lens Discussion 7 03-25-2009 03:19 PM
SR Focal Length Input for a Manual Zoom Lens? frank Pentax SLR Lens Discussion 13 03-15-2009 03:04 PM



All times are GMT -7. The time now is 07:47 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top