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### AuthorTopic: Newbe question 35mm vs MF and dof  (Read 41801 times)

#### ErikKaffehr

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##### Re: Newbe question 35mm vs MF and dof (just another way of putting it)
« Reply #60 on: January 02, 2011, 04:36:49 am »

Hi,

Assuming that CoC corresponds to the diffused area that appears sharp to the eye, why do we need anything more than 1 Megapixel?

The area of 1/30 mm CoC is 1/30^2/4*pi -> 0.00087 mm^2

The area of a 24x36 mm sensor is 864 mm^2

So resolution on 24x36 is 999000 CoC sized pixels.

Essentially, the standard DoF scales are based on 1 Megapixel resolution.

Best regards
Erik
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Erik Kaffehr

#### Bart_van_der_Wolf

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##### Re: Newbe question 35mm vs MF and dof
« Reply #61 on: January 02, 2011, 06:51:48 am »

If I had to summarize what I think the crux of David's argument is, I think he is saying that DOF should be defined as a fixed standard by choosing a CoC that represents the smallest possible size of detail that was captured on the native format (ie. one film grain, one pixel, etc) and calling this the native "DOF" of the capture.

I agree, I also think that's the crux of David's argument. If so, then he is wrong. The smallest possible size of detail in the capture plane is called resolution, a 2-dimensional metric. Resolution scales inversely with magnification after capture. All accepted definitions of DOF do not scale with magnification after capture if the parameters needed to calculate it (focal length, and focus distance, and aperture value, and COC) are kept constant. However, it makes no sense to keep the COC constant for different viewing distances (= magnification after capture). The COC should be chosen for the intended viewing conditions.

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What Nick, Bart, myself, and all the industry definitions I've ever come across agree upon is that Depth of Field is a perceptual measurement. It is, in simple terms, the measurement of what looks sharp and what doesn't. Because this is a measurement of what we see, it is constantly in flux. We want to make it a calculable answer, so we try to nail down each one of the variables with assumptions about standard print size, normal viewing distances, average human visual acuity, etc. until we get a final "number" that is the DOF. But in reality if DOF is perceptual and only exists at the moment we are seeing the image in the real world, it's never going to be a constant. We just take a measurement of a point in time and set of viewing conditions, and calculate the answer from that.

The DOF formula gives variable answers because one of its parameters is variable. At capture, focal length is fixed, aperture value is fixed, object distance is fixed, pupil factor is fixed,  but COC is variable (dependent on the intended use). The DOF can only be calculated if also a COC is chosen. The COC is a subjective quantity of acceptable unsharpness, and therefore dependent on viewer (visual acuity) and viewing conditions (output magnification), and how tolerant the viewer is towards unsharpness (even that varies).

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I think we could draw this to a close if David would answer two straightforward questions from his perspective.

1) What is the definition of DOF?
2) Assuming DOF is a fixed property (requiring a specific CoC to be chosen), how do you select what specific CoC to use, and why?

Indeed.

Cheers,
Bart
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#### Nick Rains

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##### Re: Newbe question 35mm vs MF and dof
« Reply #62 on: January 02, 2011, 08:21:15 pm »

Thanks fellas, looks like this has been set to rest...
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Nick Rains
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#### David Klepacki

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##### Re: Newbe question 35mm vs MF and dof
« Reply #63 on: January 03, 2011, 02:28:42 am »

I think everyone in this conversation has a good grasp on the fundamentals at hand. Where we are all hanging up is that we can't quite determine what David believes the definition of Depth of Field to be, and because he keeps making pronouncements about what is or isn't true about DOF (often in contradiction to what the rest of us believe to be accurate) the conversation keeps going on and on.

I think we could draw this to a close if David would answer two straightforward questions from his perspective.

1) What is the definition of DOF?
2) Assuming DOF is a fixed property (requiring a specific CoC to be chosen), how do you select what specific CoC to use, and why?

I will try my best ...

1) My definition of photographic DOF is soley based on the classical physics of optics (e.g., the well-known lens equations).  These principles and formulas describe the rendering of a three-dimensional scene onto a two dimensional medium via a system of lenses.  The CoC of the medium used to record this rendering is what fixes the DOF, along with the other optical parameters.  It is my contention that once this scene is rendered onto this medium in this manner, the DOF is an invariant quantity thereafter.  In other words, it does not change when I print it or view it on a monitor or projection screen.  What does change when viewing under these different circumstances is strictly limited by the subjective depth perception of the individual viewer, which is typically affected by the resolution of the print itself, but the DOF of the captured image can never be said to have changed.

I do not agree that DOF is a subjective quantity, and I believe that its associated CoC can be established by objective measurements.  Rather, it is the viewing resolution that gives rise to subjective depth perception.  For example, two people examining the same print at the same viewing distance can disagree about their respective perception of depth in the photo.  In fact, in the extreme case where one of these persons has lost vision in one eye, such a person will be unable to see any depth at all, since depth perception requires binocular vision.  Nevertheless, the DOF of the image itself is always objectively defined (via the optical process of rendering the original 3D scene).

2)  I think I implicitly answered your question in my above answer.  The CoC must be chosen as that of the capture medium involved in the rendering, e.g., of the film or digital sensor.  Why?  Because it is objectively measurable and not subjective, and it is the appropriate quantity that is involved in the rendering process.

So for me, DOF does not depend on print size, but I guess others wish to believe that it does.
« Last Edit: January 03, 2011, 02:31:01 am by David Klepacki »
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#### Sheldon N

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##### Re: Newbe question 35mm vs MF and dof
« Reply #64 on: January 03, 2011, 02:59:19 am »

I will try my best ...

1) My definition of photographic DOF is soley based on the classical physics of optics (e.g., the well-known lens equations).  These principles and formulas describe the rendering of a three-dimensional scene onto a two dimensional medium via a system of lenses.  The CoC of the medium used to record this rendering is what fixes the DOF, along with the other optical parameters.

I appreciate the reply, but you haven't quite defined anything. There's nothing in the above that says "DOF is.....".

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It is my contention that once this scene is rendered onto this medium in this manner, the DOF is an invariant quantity thereafter.  In other words, it does not change when I print it or view it on a monitor or projection screen.  What does change when viewing under these different circumstances is strictly limited by the subjective depth perception of the individual viewer, which is typically affected by the resolution of the print itself, but the DOF of the captured image can never be said to have changed.

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I do not agree that DOF is a subjective quantity, and I believe that its associated CoC can be established by objective measurements.

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The CoC must be chosen as that of the capture medium involved in the rendering, e.g., of the film or digital sensor.  Why?  Because it is objectively measurable and not subjective, and it is the appropriate quantity that is involved in the rendering process.

So if I may rephrase your position...   DOF is the resolution of the photographic capture regardless of whether is it visible, because it is an objectively quantifiable measurement rather than a subjective measurement.

At this point it is clear that everyone in this discussion disagrees with your position regarding what Depth of Field is, that the general industry consensus disagrees with what your definition of DOF is, and that you are not open minded to reconsider your position or admit the possibility that you are wrong or could learn something from this discussion.

My opinion is that given the above, is that it's best to simply end the conversation rather than continue to go back and forth on this and waste everyone's time.
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#### ErikKaffehr

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##### Re: Newbe question 35mm vs MF and dof
« Reply #65 on: January 03, 2011, 03:48:28 am »

Hi,

Actually I can agree that DoF is ultimately dependent on medium. The question may be if the medium is the sensor or the print? With small pitch digital sensors the area of critical focus is very narrow. My experience is that it's best to forget about DoF, CoC and hyperfocal distance. Focus on what needs to be sharp and stop down as needed, or resort to Helicon Focus (or similar).

Why not check this? http://echophoto.dnsalias.net/ekr/index.php/photoarticles/29-handling-the-dof-trap?start=2

Best regards
Erik

I appreciate the reply, but you haven't quite defined anything. There's nothing in the above that says "DOF is.....".

So if I may rephrase your position...   DOF is the resolution of the photographic capture regardless of whether is it visible, because it is an objectively quantifiable measurement rather than a subjective measurement.

At this point it is clear that everyone in this discussion disagrees with your position regarding what Depth of Field is, that the general industry consensus disagrees with what your definition of DOF is, and that you are not open minded to reconsider your position or admit the possibility that you are wrong or could learn something from this discussion.

My opinion is that given the above, is that it's best to simply end the conversation rather than continue to go back and forth on this and waste everyone's time.

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Erik Kaffehr

#### Chris Livsey

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##### Re: Newbe question 35mm vs MF and dof
« Reply #66 on: January 03, 2011, 04:36:41 am »

Thanks fellas, looks like this has been set to rest...

nice try- no chance !! This one will run and run

ChrisL
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#### Nick Rains

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##### Re: Newbe question 35mm vs MF and dof
« Reply #67 on: January 03, 2011, 04:55:18 am »

In fact, in the extreme case where one of these persons has lost vision in one eye, such a person will be unable to see any depth at all, since depth perception requires binocular vision.

There is no real depth in a print, just the 2D illusion of the 3D depth of the subject. This depth relies on many factors, one of which is what is in focus and what is not. Perspective is another, as are converging lines, aerial perspective, colour tone and so on. What is does not rely on is stereo vision! This must be the source of your misunderstanding of what we have all been saying.

Oh, and your transparency viewing scenario was, as you requested, answered in great detail by Sheldon and myself.

Eric, yes, this may be true in principle, but in practice it's quite easy to understand that any magnification of CoCs (ie making a print bigger than the original capture) changes the original assumptions and thus necessitates recalculating the DOF. This is consistent across every source.

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Nick Rains
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#### David Klepacki

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##### Re: Newbe question 35mm vs MF and dof
« Reply #68 on: January 03, 2011, 11:34:26 am »

I appreciate the reply, but you haven't quite defined anything. There's nothing in the above that says "DOF is.....".

That's because I do not disagree with any of the definitions as found in any physics textbook on classical optics.  Why must I type out well-known formulas here?  This is just asking for more wasted time, something to which you are also objecting.  Also, in a previous response I already pointed you to a randomly found website that explicitly summarizes some of the formulas appropriate to photographic capture.  You should be able to find some yourself with simple searches.

At this point it is clear that everyone in this discussion disagrees with your position regarding what Depth of Field is, that the general industry consensus disagrees with what your definition of DOF is, and that you are not open minded to reconsider your position or admit the possibility that you are wrong or could learn something from this discussion.

This is simply not true and an unfair statement.  I have given serious consideration to your position and have analyzed it thoroughly to help you refine your own understanding of DOF.  Maybe you want to reflect a bit yourself on your own open-mindedness here.

To support my claims, I have given substantial verifiable evidence.  How you can you claim that the general industry disagrees with my definition of DOF when it has been established since the time of Isaac Newton?  The equations for DOF have been known and used for hundreds of years, and if it were not for these equations, then it would not be possible to have eyeglasses, telescopes, microscopes, or any photographic equipment whatsoever.  So, exactly which industry are you referring to in your comment here where you think there is disagreement with my definition of DOF and that of these other industries that agree with me?
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#### David Klepacki

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##### Re: Newbe question 35mm vs MF and dof
« Reply #69 on: January 03, 2011, 11:54:49 am »

There is no real depth in a print, just the 2D illusion of the 3D depth of the subject.

Nick, your statement confirms exactly what I have been saying all along.  DOF is defined in terms of real depth.  It is not something that is defined by any illusion of depth.  In other words, the equations of optics that define DOF have nothing to do with the illusion of depth as it would appear on the 2D captured medium.

So, I think you actually must agree with me on my original claim in this thread:  The DOF cannot depend on print size, since real depth (DOF) and illusion of depth (print) are two entirely different things.

Do you now see your misunderstanding?  The illusion of depth in the print depends on the DOF of the captured image, but the opposite is not true.
« Last Edit: January 03, 2011, 12:15:01 pm by David Klepacki »
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#### AldoMurillo

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##### Re: Newbe question 35mm vs MF and dof
« Reply #70 on: January 03, 2011, 12:33:32 pm »

Remembering Christopher original question:

Say I take a Leica S2 with a 70mm f2.5 and compare shots with a Nikon d3x with a 50mm f 1.4, how will the dof compare:
At what f stop will the Nikon dof be approx equal to the Leica @ f 2,5?
Will this change if Nikon comes with a D4x at say 30 mp?
Is there som kind of multiplyer I can use across focalranges to get som idea of the dof similarities/differences?

Christopher

I've had the same question in mind, specially "how will the dof compare?" between 35mm and MF.   I've been using a H4D-40 for several months, and I had the D3x (now only the D700) and I still have doubts regarding the DOF.

I have and example for Christopher, please correct me if I'm wrong.

Imagine that you are taking a picture of a family with a 100mm lens, f/4 at 8 meters of distance with a Nikon D3x, Leica S2 and Hasselblad H4D-40.  Lens, f-stop, and distance doesn't change, you only change the cameras.

First you have to take notice that Leica, NIkon, and the H4d-40 have almost the same pixel density (6µm, 5.94µm and 6µm respectively) and therefore the same pixel per determinated area, or density.

The only thing that changes is the sensor size, that look something like this:

If you took the image with the H4D-40 (remembering 100mm lens, f/4 and distance of 8 meters), you could crop the image and get the "same" image of the Nikon D3x (with the same 100mm lens, f/4 and distance of 8 meters).  You will get same image size, same angle of view, same perspective view and same DoF.  That's only if you don't change any variable.

Leica S2 has more pixels horizontally.  Here's an example:

Here's an example of the angles of view:

Here's an example if you downsample the Leica S2 and H4D-40 to get the same height of the Nikon D3x.

To me the catch is in the framing and in the distance from the subject. If you would like to frame the image the same way the nikon D3x looks (tighter), with the hasselblad h4d-40 and S2 (because the bigger sensor) you will need to get closer and as we know the closer you get to the subject at any fstop, the shallower DoF we get.

I would say that with the Hasselblad H4d-40, framing the same way (closer distance to the subject) at f/4 the DOF will look like f/2.8 in the nikon D3x or about 2 stops, that's just my opinion, nothing scientific    , of course the perspective view would be different between the 2 images.

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Aldo Murillo

#### David Klepacki

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##### Re: Newbe question 35mm vs MF and dof
« Reply #71 on: January 03, 2011, 12:55:30 pm »

Yes, Aldo this is basically correct.  All else being equal, the object size at the sensor in relation to the sensor size itself will determine its DOF.  Since larger formats have wider angle of views for a given focal length and shooting distance, the reduction in only the shooting distance with the larger format can be made to reduce its DOF to match that of a smaller format as long as it is within the ability of the lens to do so.  To calculate this exactly, you would have to work through the equations for DOF.  Of course, with two different lenses, it is much more complicated to compare exactly due to their MTF characteristics, and the fact that some cameras (like the D3X) apply additional filtering before hitting its sensor.  However, for all practical purposes, you have the right idea.

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#### jeremypayne

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##### Re: Newbe question 35mm vs MF and dof
« Reply #72 on: January 03, 2011, 01:17:16 pm »

What a circle jerk!  One of the most humorous threads - ever, anywhere! ... (if you like boring threads on photography) ...  I've been laid up with a minor leg injury and this thread has been a mainstay of my convalescence.

I think we need to coin a new term for what David is trying to articulate ... I propose "Focus Falloff".

"Depth of Field" is a perceptual phenomenon that requires assumptions about what "sharp enough" means ... which clearly means image size, viewing distance, visual acuity and taste all matter.

Focus Falloff is the other thing ... the thing that David thinks is Depth of Field.

They are obviously related.
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#### David Klepacki

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##### Re: Newbe question 35mm vs MF and dof
« Reply #73 on: January 03, 2011, 01:23:34 pm »

Jeremy, Try consulting a textbook on optics. If I am indeed wrong, then the entire scientific community is wrong with regard to their notion of DOF.  This is quite a preposterous claim.

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#### jeremypayne

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##### Re: Newbe question 35mm vs MF and dof
« Reply #74 on: January 03, 2011, 02:18:07 pm »

Jeremy, Try consulting a textbook on optics. If I am indeed wrong, then the entire scientific community is wrong with regard to their notion of DOF.  This is quite a preposterous claim.

Ok ... superfluous given the rest of this thread ... but here goes ...

"Total DOF(s>>f ) ~=  2 faCs2/(( fa)2-(sC)2) =  2 as2( f/C)/(( f/C)2a2 - s2)

The circle of confusion C at the DOF limit is based on the 0.01 inch = 0.25 mm feature in an 8x10 inch print."

http://www.normankoren.com/Tutorials/MTF6.html#DOF_diffraction
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#### Doug Peterson

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##### Re: Newbe question 35mm vs MF and dof
« Reply #75 on: January 03, 2011, 02:29:02 pm »

Ok ... superfluous given the rest of this thread ... but here goes ...

"Total DOF(s>>f ) ~=  2 faCs2/(( fa)2-(sC)2) =  2 as2( f/C)/(( f/C)2a2 - s2)

The circle of confusion C at the DOF limit is based on the 0.01 inch = 0.25 mm feature in an 8x10 inch print."

http://www.normankoren.com/Tutorials/MTF6.html#DOF_diffraction

That's not very relevant for someone shooting predominately for websites (800 pixel wide product shot), printed catalogs (2" wide product shot), or 2 meter wide prints.

#### jeremypayne

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##### Re: Newbe question 35mm vs MF and dof
« Reply #76 on: January 03, 2011, 02:43:06 pm »

That's not very relevant for someone shooting predominately for websites (800 pixel wide product shot), printed catalogs (2" wide product shot), or 2 meter wide prints.

I agree ... it was relevant to me when I was shooting 35mm Pan-X and making small darkroom prints (25 years ago).

But ... with 20/10 vision (amazing laser correction), 50MP files and 24 inch prints ... we need new assumptions about what is "acceptably sharp" ... so we can make better assumptions about the CoC to put in the little calculator ... so we can ignore them in the field.

Like Erik, these days I focus on what I want sharp, stop down if I want more "depth of field" ... and try to be mindful of diffraction.  I leave my calculators at home ...
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#### David Klepacki

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##### Re: Newbe question 35mm vs MF and dof
« Reply #77 on: January 03, 2011, 03:14:22 pm »

Ok ... superfluous given the rest of this thread ... but here goes ...

"Total DOF(s>>f ) ~=  2 faCs2/(( fa)2-(sC)2) =  2 as2( f/C)/(( f/C)2a2 - s2)

The circle of confusion C at the DOF limit is based on the 0.01 inch = 0.25 mm feature in an 8x10 inch print."

http://www.normankoren.com/Tutorials/MTF6.html#DOF_diffraction

Jeremy, The DOF equations require parameters that are involved in the actual rendering process of the 3D scene (consult the diagrams as well as the equations associated with them).  You cannot blindly substitute other CoC values that have nothing to do with the rendering process, such as those associated with viewing a print.  As Nick has already pointed out above, the print only contains an illusion of depth in a 2D space.  For example, the CoC of the print will depend on things like the size of the inkjet drop, and the absorption characteristics of the paper or other substrate being used at the time of printing, which have nothing to do with the image capture.  However, the actual image as captured on film or by the digital sensor would always have a well defined DOF according to its optical definition, and with whatever CoC value of the film or sensor being used.  DOF is only defined in optics and only during the rendering of a 3D scene onto a 2D plane via a lens, and only the features of the 2D plane involved in this process is what is involved in these equations.  You can manipulate the captured image all you want afterward (projecting, printing, sharpening, blurring, etc.), but that no longer belongs to the realm of optics and the concept of DOF.
« Last Edit: January 03, 2011, 03:17:03 pm by David Klepacki »
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#### jeremypayne

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##### Re: Newbe question 35mm vs MF and dof
« Reply #78 on: January 03, 2011, 03:18:04 pm »

Jeremy, The DOF equations require parameters that are involved in the actual rendering process of the 3D scene (consult the diagrams as well as the equations associated with them).  You cannot blindly substitute other CoC values that have nothing to do with the rendering process, such as those associated with viewing a print.  As Nick has already pointed out above, the print only contains an illusion of depth in a 2D space.  For example, the CoC of the print will depend on things like the size of the inkjet drop, and the absorption characteristics of the paper or other substrate being used at the time of printing, which have nothing to do with the image capture.  However, the actual image as captured on film or by the digital sensor would always have a well defined DOF according to its optical definition, and with whatever CoC value of the film or sensor being used.  DOF is only defined in optics and only during the rendering of a 3D scene onto a 2D plane via a lens, and only the features of the 2D plane involved in this process is what is involved in these equations.  You can manipulate the captured image all you want afterward (viewing, printing, sharpening, blurring, etc.), but that no longer belongs to the realm of optics and the concept of DOF.

Ok, dude ... whatever ...

You are talking about "focus falloff" ... not "depth of field" ... the rest of us are talking about "depth of field".
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#### Bart_van_der_Wolf

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##### Re: Newbe question 35mm vs MF and dof
« Reply #79 on: January 03, 2011, 03:30:26 pm »

However, the actual image as captured on film or by the digital sensor would always have a well defined DOF according to its optical definition, and with whatever CoC value of the film or sensor being used.

David,

You are confusing resolution in the imaging plane with DOF. The definition of DOF has an assumed COC as parameter. Without the COC parameter, DOF cannot be calculated. Use a different COC, and you'll get a different DOF.

Cheers,
Bart
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