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Thread started 21 Jan 2018 (Sunday) 11:42
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Depth of Field Calculator inconsistencies

 
mwsilver
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Jan 21, 2018 11:42 |  #1

Like some here I have used the Dofmaster online site for DoF calculations. Over time I have also downloaded and tried out a variety of DoF apps for my Android phone. What I had quickly discovered was that the results from the Android apps almost all differ from each other as well as from Dofmaster, sometimes by large amounts. Most of the time, the difference is not significant enough to cause any problems. However, I wonder if others have seen the same thing, can identify the best phone app to use, and explain why the calculations would differ from app to app and to Dofmaster. In my ignorance, I would assume that these calculators are using some sort of standard DoF calculations and should be almost identical. I have searched online on several occasions but have not yet found a useful answer


Mark
Canon 7D2, 60D, T3i, T2i, Sigma 18-35 f/1.8, 30 f/1.4. Canon EF 70-200 L f/4 IS, EF 35 f/2 IS, EFs 10-18 STM, EFs 15-85, EFs 18-200, EF 50 f/1.8 STM, Tamron 18-270 PZD, B+W MRC CPL, Canon 320EX, Vanguard Alta Pro 254CT & SBH 250 head. RODE Stereo Videomic Pro, DXO PhotoLab, Elements 15

  
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s1a1om
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Post edited 6 months ago by s1a1om. (4 edits in all)
     
Jan 21, 2018 12:46 |  #2

I would guess it's due to slight different assumptions. Not necessarily that any of them are "wrong". One of the easiest places to get differences is by assuming a slightly different value circle of confusion. There are certainly wrong values that could be used here, but there are also a number of slightly different ones that could be correct as well.

Why not write your own spreadsheet or script to calculate it and compare with the calculators you found online. You can find the necessary equations on Wikipedia
https://en.wikipedia.o​rg …pth_of_field#DO​F_formulae (external link)

Some information on the circle of confusion: https://en.wikipedia.o​rg/wiki/Circle_of_conf​usion (external link)

Wikipedia wrote:
In photography, the circle of confusion diameter limit (“CoC”) for the final image is often defined as the largest blur spot that will still be perceived by the human eye as a point.

With this definition, the CoC in the original image (the image on the film or electronic sensor) 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, a final image larger than 8″×10″ will be viewed at a distance correspondingly greater than 25 cm, and for which a larger CoC may be acceptable; the original-image CoC is then the same as that determined from the standard final-image size and viewing distance. But if the larger final image will be viewed at the normal distance of 25 cm, a smaller original-image CoC will be needed to provide acceptable sharpness.
3. Enlargement from the original image to the final image. If there is no enlargement (e.g., a contact print of an 8×10 original image), the CoC for the original image is the same as that in the final image. But if, for example, the long dimension of a 35 mm original image is enlarged to 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.

The common values for CoC may not be applicable if reproduction or viewing conditions differ significantly from those assumed in determining those values. If the original image will be given greater enlargement, or viewed at a closer distance, then a smaller CoC will be required. All three factors above are accommodated with this formula


Constructive criticism is always appreciated.

  
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mwsilver
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Jan 21, 2018 14:06 |  #3

s1a1om wrote in post #18545851 (external link)
I would guess it's due to slight different assumptions. Not necessarily that any of them are "wrong". One of the easiest places to get differences is by assuming a slightly different value circle of confusion. There are certainly wrong values that could be used here, but there are also a number of slightly different ones that could be correct as well.

Why not write your own spreadsheet or script to calculate it and compare with the calculators you found online. You can find the necessary equations on Wikipedia
https://en.wikipedia.o​rg …pth_of_field#DO​F_formulae (external link)

Some information on the circle of confusion: https://en.wikipedia.o​rg/wiki/Circle_of_conf​usion (external link)

Thanks. From additional research I'm currently doing it appears that the main culprit maybe the differences in circles of confusion, which I understand is not a standard value.


Mark
Canon 7D2, 60D, T3i, T2i, Sigma 18-35 f/1.8, 30 f/1.4. Canon EF 70-200 L f/4 IS, EF 35 f/2 IS, EFs 10-18 STM, EFs 15-85, EFs 18-200, EF 50 f/1.8 STM, Tamron 18-270 PZD, B+W MRC CPL, Canon 320EX, Vanguard Alta Pro 254CT & SBH 250 head. RODE Stereo Videomic Pro, DXO PhotoLab, Elements 15

  
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Wilt
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Post edited 6 months ago by Wilt. (8 edits in all)
     
Jan 21, 2018 14:37 |  #4

mwsilver wrote in post #18545813 (external link)
Like some here I have used the Dofmaster online site for DoF calculations. Over time I have also downloaded and tried out a variety of DoF apps for my Android phone. What I had quickly discovered was that the results from the Android apps almost all differ from each other as well as from Dofmaster, sometimes by large amounts. Most of the time, the difference is not significant enough to cause any problems. However, I wonder if others have seen the same thing, can identify the best phone app to use, and explain why the calculations would differ from app to app and to Dofmaster. In my ignorance, I would assume that these calculators are using some sort of standard DoF calculations and should be almost identical. I have searched online on several occasions but have not yet found a useful answer


Here is the REASON for the lack of consistency between various DOF programs...

First begin with the understanding that the CofC value is based upon an ASSUMPTION of using an 8x10" print which is viewed from 12" away, and the actual DOF calculator CofC valueassumes some level of magnification of the in-camera image to arrive at final 8x10" print size... APS-C image is enlarged about 13.5X, FF image is enlarged about 8.5X; the CofC for each format size is simply

CofC (at 8x10) / mag factor used to make print

Now the important part (pertinent to your question), you need to understand that the CofC value (in the 8x10" print) makes assumptions about the viewer being able to SEE a 'blur circle' which is the out-of-focus representation of a perfect point.
Most DOF programs assume 'manufacturer standard' and that is far less visual acuity than the 20/20 goal that optometrists try to get our corrected vision to equal! And even then there is NOT a single universal value used by all...

  • The DOFmaster that you linked assumed APS-C CofC of 0.019mm
  • The so-called 'Zeiss formula' is a supposed formula for computing a circle of confusion (CoC) criterion for depth of field (DoF) calculations.

    The formula is c=d/1730,

    where d is the diagonal measure of a camera format, film, sensor, or print, and c the maximum acceptable diameter of the circle of confusion, so 'Zeiss formula' value of CofC is 0.01563

  • the common 'manufacturer standard'... "All the camera lens manufacturers in the world including Carl Zeiss have to adhere to the same principle and the international standard that is based upon it (0.03mm for the 35mm format), when producing their depth of field scales and tables." or an APS-C CofC of 0.0187mm


... yet Zeiss itself gives the values d/1000 as the traditional standard and d/1500 as the modern standard. If d/1500, CofC is 0.0180

The fundamental issue is also what is assumed to be the quantification of human visual acuity ... which is often stated as detail as small as 'one minute of arc',
and yet you also read it described '30 seconds (one half minute) of arc'

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mwsilver
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Jan 21, 2018 14:57 |  #5

Wilt wrote in post #18545939 (external link)
Here is the REASON for the lack of consistency between various DOF programs...

First begin with the understanding that the CofC value is based upon an ASSUMPTION of using an 8x10" print which is viewed from 12" away, and the actual DOF calculator CofC valueassumes some level of magnification of the in-camera image to arrive at final 8x10" print size... APS-C image is enlarged about 13.5X, FF image is enlarged about 8.5X; the CofC for each format size is simply

CofC (at 8x10) / mag factor used to make print

Now the important part (pertinent to your question), you need to understand that the CofC value (in the 8x10" print) makes assumptions about the viewer being able to SEE a 'blur circle' which is the out-of-focus representation of a perfect point.
Most DOF programs assume 'manufacturer standard' and that is far less visual acuity than the 20/20 goal that optometrists try to get our corrected vision to equal! And even then there is NOT a single universal value used by all...

  • The DOFmaster that you linked assumed APS-C CofC of 0.019mm
  • The so-called 'Zeiss formula' is a supposed formula for computing a circle of confusion (CoC) criterion for depth of field (DoF) calculations.
    The formula is c=d/1730,
    where d is the diagonal measure of a camera format, film, sensor, or print, and c the maximum acceptable diameter of the circle of confusion, so 'Zeiss formula' value of CofC is 0.01563
  • the common 'manufacturer standard'... "All the camera lens manufacturers in the world including Carl Zeiss have to adhere to the same principle and the international standard that is based upon it (0.03mm for the 35mm format), when producing their depth of field scales and tables." or an APS-C CofC of 0.0187mm


... yet Zeiss itself gives the values d/1000 as the traditional standard and d/1500 as the modern standard. If d/1500, CofC is 0.0180

The fundamental issue is also what is assumed to be the quantification of human visual acuity ... which is often stated as detail as small as 'one minute of arc',
and yet you also read it described '30 seconds (one half minute) of arc'

Thanks. That helps a lot.


Mark
Canon 7D2, 60D, T3i, T2i, Sigma 18-35 f/1.8, 30 f/1.4. Canon EF 70-200 L f/4 IS, EF 35 f/2 IS, EFs 10-18 STM, EFs 15-85, EFs 18-200, EF 50 f/1.8 STM, Tamron 18-270 PZD, B+W MRC CPL, Canon 320EX, Vanguard Alta Pro 254CT & SBH 250 head. RODE Stereo Videomic Pro, DXO PhotoLab, Elements 15

  
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Depth of Field Calculator inconsistencies
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