What is “focus distance lower/upper” and how is it different from depth of field?Why did manufacturers stop including DOF scales on lenses?How to estimate depth of field?Why do depth of field calculators show *more* DOF for larger formats with the same lens parameters?How to calculate depth of field by using extension tubesdoes depth of field travel with the focal plane?Invariants in subject size and depth of field?How do depth of field and the circle of confusion relate to pixel size on the sensor?Why I am getting different values for depth of field from calculators vs in-camera DoF preview?How do I calculate the depth of field of cameras on mobile phones with auto focus?depth of field and f-stopAre all prime lenses designed so that the same DoF scale applies at any focusing distance? If so, why?

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What is “focus distance lower/upper” and how is it different from depth of field?


Why did manufacturers stop including DOF scales on lenses?How to estimate depth of field?Why do depth of field calculators show *more* DOF for larger formats with the same lens parameters?How to calculate depth of field by using extension tubesdoes depth of field travel with the focal plane?Invariants in subject size and depth of field?How do depth of field and the circle of confusion relate to pixel size on the sensor?Why I am getting different values for depth of field from calculators vs in-camera DoF preview?How do I calculate the depth of field of cameras on mobile phones with auto focus?depth of field and f-stopAre all prime lenses designed so that the same DoF scale applies at any focusing distance? If so, why?













3















I have taken two photographs on a Canon crop sensor camera: 18mm f/9 with the following exiftool output (the focus was approximately at 3.5 meters):



Focus Distance Upper : 5.27 m
Focus Distance Lower : 1.82 m
Depth Of Field : inf (1.24 m - inf)


And 50mm f/1.8 with the following exiftool output:



Focus Distance Upper : 1.99 m
Focus Distance Lower : 1.41 m
Depth Of Field : 0.08 m (1.66 - 1.74 m)


Now, I assume I know what depth of field means. It's the same thing as the one that will be given by a depth of field calculator such as http://www.dofmaster.com/dofjs.html



But what are Focus Distance Upper and Focus Distance Lower?



Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?










share|improve this question
























  • Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel peeping.

    – Michael C
    2 days ago















3















I have taken two photographs on a Canon crop sensor camera: 18mm f/9 with the following exiftool output (the focus was approximately at 3.5 meters):



Focus Distance Upper : 5.27 m
Focus Distance Lower : 1.82 m
Depth Of Field : inf (1.24 m - inf)


And 50mm f/1.8 with the following exiftool output:



Focus Distance Upper : 1.99 m
Focus Distance Lower : 1.41 m
Depth Of Field : 0.08 m (1.66 - 1.74 m)


Now, I assume I know what depth of field means. It's the same thing as the one that will be given by a depth of field calculator such as http://www.dofmaster.com/dofjs.html



But what are Focus Distance Upper and Focus Distance Lower?



Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?










share|improve this question
























  • Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel peeping.

    – Michael C
    2 days ago













3












3








3


1






I have taken two photographs on a Canon crop sensor camera: 18mm f/9 with the following exiftool output (the focus was approximately at 3.5 meters):



Focus Distance Upper : 5.27 m
Focus Distance Lower : 1.82 m
Depth Of Field : inf (1.24 m - inf)


And 50mm f/1.8 with the following exiftool output:



Focus Distance Upper : 1.99 m
Focus Distance Lower : 1.41 m
Depth Of Field : 0.08 m (1.66 - 1.74 m)


Now, I assume I know what depth of field means. It's the same thing as the one that will be given by a depth of field calculator such as http://www.dofmaster.com/dofjs.html



But what are Focus Distance Upper and Focus Distance Lower?



Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?










share|improve this question
















I have taken two photographs on a Canon crop sensor camera: 18mm f/9 with the following exiftool output (the focus was approximately at 3.5 meters):



Focus Distance Upper : 5.27 m
Focus Distance Lower : 1.82 m
Depth Of Field : inf (1.24 m - inf)


And 50mm f/1.8 with the following exiftool output:



Focus Distance Upper : 1.99 m
Focus Distance Lower : 1.41 m
Depth Of Field : 0.08 m (1.66 - 1.74 m)


Now, I assume I know what depth of field means. It's the same thing as the one that will be given by a depth of field calculator such as http://www.dofmaster.com/dofjs.html



But what are Focus Distance Upper and Focus Distance Lower?



Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?







autofocus focus metadata depth-of-field






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 2 days ago









mattdm

122k40357653




122k40357653










asked 2 days ago









juhistjuhist

589112




589112












  • Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel peeping.

    – Michael C
    2 days ago

















  • Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel peeping.

    – Michael C
    2 days ago
















Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel peeping.

– Michael C
2 days ago





Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel peeping.

– Michael C
2 days ago










3 Answers
3






active

oldest

votes


















7














The Focus Distance Upper and Focus Distance Lower tags are in the Canon-proprietary "maker notes" and aren't part of standard EXIF, so documentation is scarce. However, it appears that these (together) represent the distance at which the lens's focus is set. That is, it's somewhere between the two bounds.



Why Canon does it this way rather than providing a single value (perhaps with second uncertainty or error value) is a mystery only Canon could resolve, and they don't seem to have publicly. Here's a forum post with some investigation: Re: Distance in EXIF.



Note also that Depth of Field is an exiftool composite tag. The information there is not set directly by the camera — instead, Exiftool generates this from other data, including whatever hint it gets as to focus distance. From the docs, it looks like it uses the Upper and Lower values, but also other info, which may explain the disparity you note.



In any case these values are approximate and should be taken as hints, rather than as gospel. Their original purpose is probably to hint at subject distance to aid the camera in making TTL flash power computations. They're not meant to be scientific measurements, or even photographic scene information (like GPS location tags or something).






share|improve this answer

























  • @chrylis yes, thanks. perils of answering on one's phone and all that.

    – mattdm
    2 days ago






  • 1





    I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

    – WayneF
    2 days ago












  • @WayneF yeah, the forum post exploration supports that guess.

    – mattdm
    2 days ago


















3














As @mattdm found out, the FocusDistanceLower and FocusDistanceUpper, whatever they exactly mean, together denote the approximate focus distance. ExifTool then calculates depth of field based on these.



I took a look at the ExifTool source code, and the DoF calculation desires:



Desire => 
3 => 'FocusDistance', # focus distance in metres (0 is infinity)
4 => 'SubjectDistance',
5 => 'ObjectDistance',
6 => 'ApproximateFocusDistance ',
7 => 'FocusDistanceLower',
8 => 'FocusDistanceUpper',
,


And if focus distance is not defined (all of 3, 4, 5 and 6 are undefined), it is calculated as follows:



$d = ($val[7] + $val[8]) / 2;


So, ExifTool is simply using the arithmetic mean of the two focus distances. Not sure if that's correct or if it's just an educated guess.



Anyway, this probably doesn't matter as I don't trust in the accuracy of focus distance fields more than I would trust in the focus distance meter on a lens that happens to have one.






share|improve this answer






























    1














    Imagine a train track with detectors every 2 miles that will detect the presence of a train. Also imagine that we have a transponder placed near the middle of the train that triggers the detectors when it passes.



    If a very short express train less than a quarter mile in length has passed mile 6 but has not yet reached mile 8, the best that the system can tell anyone is that the train is somewhere between mile 6 and mile 8.



    Now consider that we have a very long, heavy freight train that is three miles long. At times our three mile long train will be next to two detectors, with the transponder in between. At other times, when the transponder is within one-half mile of a detector, the train will only be next to one detector. When the transponder is between detectors, we still won't know exactly where the head end of the train is.



    Basically, the sensors in the lens that report distance information to the camera are like the detectors every two miles along our train track. They tell the camera what positions the lens is focused between. The "Focus Distance Lower" is the closest position the lens might currently be focused at. The "Focus Distance Upper" is the furthest position the lens might currently be focused. The lens might actually be focussed anywhere within that range.




    Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?




    The depth of field is like the length of our train. With a wide aperture, we have a short express train. With a narrow aperture, we have a long freight train. We only can sense when the focus distance in the middle of the DoF crosses from one detection zone to the next, just as we only have a transponder in the middle of our train. With a deeper DoF the edges of the DoF may or may not be past the "Upper" and "Lower" focus distance, but we can't know that since only the position of the actual focus distance can be measured as anywhere between two of the detectors at various positions between minimum focus distance and infinity.



    The camera only reports the range of the actual focus distance, the focal length, and the aperture used. EXIF Info makes an educated guess at the DoF based on combining those three factors.



    In the end, DoF calculations are only estimates. Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel-peeping.






    share|improve this answer

























    • This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

      – juhist
      yesterday










    Your Answer








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    3 Answers
    3






    active

    oldest

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    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    7














    The Focus Distance Upper and Focus Distance Lower tags are in the Canon-proprietary "maker notes" and aren't part of standard EXIF, so documentation is scarce. However, it appears that these (together) represent the distance at which the lens's focus is set. That is, it's somewhere between the two bounds.



    Why Canon does it this way rather than providing a single value (perhaps with second uncertainty or error value) is a mystery only Canon could resolve, and they don't seem to have publicly. Here's a forum post with some investigation: Re: Distance in EXIF.



    Note also that Depth of Field is an exiftool composite tag. The information there is not set directly by the camera — instead, Exiftool generates this from other data, including whatever hint it gets as to focus distance. From the docs, it looks like it uses the Upper and Lower values, but also other info, which may explain the disparity you note.



    In any case these values are approximate and should be taken as hints, rather than as gospel. Their original purpose is probably to hint at subject distance to aid the camera in making TTL flash power computations. They're not meant to be scientific measurements, or even photographic scene information (like GPS location tags or something).






    share|improve this answer

























    • @chrylis yes, thanks. perils of answering on one's phone and all that.

      – mattdm
      2 days ago






    • 1





      I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

      – WayneF
      2 days ago












    • @WayneF yeah, the forum post exploration supports that guess.

      – mattdm
      2 days ago















    7














    The Focus Distance Upper and Focus Distance Lower tags are in the Canon-proprietary "maker notes" and aren't part of standard EXIF, so documentation is scarce. However, it appears that these (together) represent the distance at which the lens's focus is set. That is, it's somewhere between the two bounds.



    Why Canon does it this way rather than providing a single value (perhaps with second uncertainty or error value) is a mystery only Canon could resolve, and they don't seem to have publicly. Here's a forum post with some investigation: Re: Distance in EXIF.



    Note also that Depth of Field is an exiftool composite tag. The information there is not set directly by the camera — instead, Exiftool generates this from other data, including whatever hint it gets as to focus distance. From the docs, it looks like it uses the Upper and Lower values, but also other info, which may explain the disparity you note.



    In any case these values are approximate and should be taken as hints, rather than as gospel. Their original purpose is probably to hint at subject distance to aid the camera in making TTL flash power computations. They're not meant to be scientific measurements, or even photographic scene information (like GPS location tags or something).






    share|improve this answer

























    • @chrylis yes, thanks. perils of answering on one's phone and all that.

      – mattdm
      2 days ago






    • 1





      I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

      – WayneF
      2 days ago












    • @WayneF yeah, the forum post exploration supports that guess.

      – mattdm
      2 days ago













    7












    7








    7







    The Focus Distance Upper and Focus Distance Lower tags are in the Canon-proprietary "maker notes" and aren't part of standard EXIF, so documentation is scarce. However, it appears that these (together) represent the distance at which the lens's focus is set. That is, it's somewhere between the two bounds.



    Why Canon does it this way rather than providing a single value (perhaps with second uncertainty or error value) is a mystery only Canon could resolve, and they don't seem to have publicly. Here's a forum post with some investigation: Re: Distance in EXIF.



    Note also that Depth of Field is an exiftool composite tag. The information there is not set directly by the camera — instead, Exiftool generates this from other data, including whatever hint it gets as to focus distance. From the docs, it looks like it uses the Upper and Lower values, but also other info, which may explain the disparity you note.



    In any case these values are approximate and should be taken as hints, rather than as gospel. Their original purpose is probably to hint at subject distance to aid the camera in making TTL flash power computations. They're not meant to be scientific measurements, or even photographic scene information (like GPS location tags or something).






    share|improve this answer















    The Focus Distance Upper and Focus Distance Lower tags are in the Canon-proprietary "maker notes" and aren't part of standard EXIF, so documentation is scarce. However, it appears that these (together) represent the distance at which the lens's focus is set. That is, it's somewhere between the two bounds.



    Why Canon does it this way rather than providing a single value (perhaps with second uncertainty or error value) is a mystery only Canon could resolve, and they don't seem to have publicly. Here's a forum post with some investigation: Re: Distance in EXIF.



    Note also that Depth of Field is an exiftool composite tag. The information there is not set directly by the camera — instead, Exiftool generates this from other data, including whatever hint it gets as to focus distance. From the docs, it looks like it uses the Upper and Lower values, but also other info, which may explain the disparity you note.



    In any case these values are approximate and should be taken as hints, rather than as gospel. Their original purpose is probably to hint at subject distance to aid the camera in making TTL flash power computations. They're not meant to be scientific measurements, or even photographic scene information (like GPS location tags or something).







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited 2 days ago

























    answered 2 days ago









    mattdmmattdm

    122k40357653




    122k40357653












    • @chrylis yes, thanks. perils of answering on one's phone and all that.

      – mattdm
      2 days ago






    • 1





      I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

      – WayneF
      2 days ago












    • @WayneF yeah, the forum post exploration supports that guess.

      – mattdm
      2 days ago

















    • @chrylis yes, thanks. perils of answering on one's phone and all that.

      – mattdm
      2 days ago






    • 1





      I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

      – WayneF
      2 days ago












    • @WayneF yeah, the forum post exploration supports that guess.

      – mattdm
      2 days ago
















    @chrylis yes, thanks. perils of answering on one's phone and all that.

    – mattdm
    2 days ago





    @chrylis yes, thanks. perils of answering on one's phone and all that.

    – mattdm
    2 days ago




    1




    1





    I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

    – WayneF
    2 days ago






    I have no clue what the meaning of two focus distances might be, but just thinking about how it might originate..The camera can only obtain the distance from the lens rotation. Which cannot be a continuous value, it has to be reported as steps of rotation. It seems reasonable to assume these two adjacent values are the possible steps that can be reported. My guess is that true value is not the mean, it's just between these two. Look at the lens distance scale, how close together these two have to be. I think Nikon simply reports the one that is reported, so not very precise either.

    – WayneF
    2 days ago














    @WayneF yeah, the forum post exploration supports that guess.

    – mattdm
    2 days ago





    @WayneF yeah, the forum post exploration supports that guess.

    – mattdm
    2 days ago













    3














    As @mattdm found out, the FocusDistanceLower and FocusDistanceUpper, whatever they exactly mean, together denote the approximate focus distance. ExifTool then calculates depth of field based on these.



    I took a look at the ExifTool source code, and the DoF calculation desires:



    Desire => 
    3 => 'FocusDistance', # focus distance in metres (0 is infinity)
    4 => 'SubjectDistance',
    5 => 'ObjectDistance',
    6 => 'ApproximateFocusDistance ',
    7 => 'FocusDistanceLower',
    8 => 'FocusDistanceUpper',
    ,


    And if focus distance is not defined (all of 3, 4, 5 and 6 are undefined), it is calculated as follows:



    $d = ($val[7] + $val[8]) / 2;


    So, ExifTool is simply using the arithmetic mean of the two focus distances. Not sure if that's correct or if it's just an educated guess.



    Anyway, this probably doesn't matter as I don't trust in the accuracy of focus distance fields more than I would trust in the focus distance meter on a lens that happens to have one.






    share|improve this answer



























      3














      As @mattdm found out, the FocusDistanceLower and FocusDistanceUpper, whatever they exactly mean, together denote the approximate focus distance. ExifTool then calculates depth of field based on these.



      I took a look at the ExifTool source code, and the DoF calculation desires:



      Desire => 
      3 => 'FocusDistance', # focus distance in metres (0 is infinity)
      4 => 'SubjectDistance',
      5 => 'ObjectDistance',
      6 => 'ApproximateFocusDistance ',
      7 => 'FocusDistanceLower',
      8 => 'FocusDistanceUpper',
      ,


      And if focus distance is not defined (all of 3, 4, 5 and 6 are undefined), it is calculated as follows:



      $d = ($val[7] + $val[8]) / 2;


      So, ExifTool is simply using the arithmetic mean of the two focus distances. Not sure if that's correct or if it's just an educated guess.



      Anyway, this probably doesn't matter as I don't trust in the accuracy of focus distance fields more than I would trust in the focus distance meter on a lens that happens to have one.






      share|improve this answer

























        3












        3








        3







        As @mattdm found out, the FocusDistanceLower and FocusDistanceUpper, whatever they exactly mean, together denote the approximate focus distance. ExifTool then calculates depth of field based on these.



        I took a look at the ExifTool source code, and the DoF calculation desires:



        Desire => 
        3 => 'FocusDistance', # focus distance in metres (0 is infinity)
        4 => 'SubjectDistance',
        5 => 'ObjectDistance',
        6 => 'ApproximateFocusDistance ',
        7 => 'FocusDistanceLower',
        8 => 'FocusDistanceUpper',
        ,


        And if focus distance is not defined (all of 3, 4, 5 and 6 are undefined), it is calculated as follows:



        $d = ($val[7] + $val[8]) / 2;


        So, ExifTool is simply using the arithmetic mean of the two focus distances. Not sure if that's correct or if it's just an educated guess.



        Anyway, this probably doesn't matter as I don't trust in the accuracy of focus distance fields more than I would trust in the focus distance meter on a lens that happens to have one.






        share|improve this answer













        As @mattdm found out, the FocusDistanceLower and FocusDistanceUpper, whatever they exactly mean, together denote the approximate focus distance. ExifTool then calculates depth of field based on these.



        I took a look at the ExifTool source code, and the DoF calculation desires:



        Desire => 
        3 => 'FocusDistance', # focus distance in metres (0 is infinity)
        4 => 'SubjectDistance',
        5 => 'ObjectDistance',
        6 => 'ApproximateFocusDistance ',
        7 => 'FocusDistanceLower',
        8 => 'FocusDistanceUpper',
        ,


        And if focus distance is not defined (all of 3, 4, 5 and 6 are undefined), it is calculated as follows:



        $d = ($val[7] + $val[8]) / 2;


        So, ExifTool is simply using the arithmetic mean of the two focus distances. Not sure if that's correct or if it's just an educated guess.



        Anyway, this probably doesn't matter as I don't trust in the accuracy of focus distance fields more than I would trust in the focus distance meter on a lens that happens to have one.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 2 days ago









        juhistjuhist

        589112




        589112





















            1














            Imagine a train track with detectors every 2 miles that will detect the presence of a train. Also imagine that we have a transponder placed near the middle of the train that triggers the detectors when it passes.



            If a very short express train less than a quarter mile in length has passed mile 6 but has not yet reached mile 8, the best that the system can tell anyone is that the train is somewhere between mile 6 and mile 8.



            Now consider that we have a very long, heavy freight train that is three miles long. At times our three mile long train will be next to two detectors, with the transponder in between. At other times, when the transponder is within one-half mile of a detector, the train will only be next to one detector. When the transponder is between detectors, we still won't know exactly where the head end of the train is.



            Basically, the sensors in the lens that report distance information to the camera are like the detectors every two miles along our train track. They tell the camera what positions the lens is focused between. The "Focus Distance Lower" is the closest position the lens might currently be focused at. The "Focus Distance Upper" is the furthest position the lens might currently be focused. The lens might actually be focussed anywhere within that range.




            Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?




            The depth of field is like the length of our train. With a wide aperture, we have a short express train. With a narrow aperture, we have a long freight train. We only can sense when the focus distance in the middle of the DoF crosses from one detection zone to the next, just as we only have a transponder in the middle of our train. With a deeper DoF the edges of the DoF may or may not be past the "Upper" and "Lower" focus distance, but we can't know that since only the position of the actual focus distance can be measured as anywhere between two of the detectors at various positions between minimum focus distance and infinity.



            The camera only reports the range of the actual focus distance, the focal length, and the aperture used. EXIF Info makes an educated guess at the DoF based on combining those three factors.



            In the end, DoF calculations are only estimates. Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel-peeping.






            share|improve this answer

























            • This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

              – juhist
              yesterday















            1














            Imagine a train track with detectors every 2 miles that will detect the presence of a train. Also imagine that we have a transponder placed near the middle of the train that triggers the detectors when it passes.



            If a very short express train less than a quarter mile in length has passed mile 6 but has not yet reached mile 8, the best that the system can tell anyone is that the train is somewhere between mile 6 and mile 8.



            Now consider that we have a very long, heavy freight train that is three miles long. At times our three mile long train will be next to two detectors, with the transponder in between. At other times, when the transponder is within one-half mile of a detector, the train will only be next to one detector. When the transponder is between detectors, we still won't know exactly where the head end of the train is.



            Basically, the sensors in the lens that report distance information to the camera are like the detectors every two miles along our train track. They tell the camera what positions the lens is focused between. The "Focus Distance Lower" is the closest position the lens might currently be focused at. The "Focus Distance Upper" is the furthest position the lens might currently be focused. The lens might actually be focussed anywhere within that range.




            Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?




            The depth of field is like the length of our train. With a wide aperture, we have a short express train. With a narrow aperture, we have a long freight train. We only can sense when the focus distance in the middle of the DoF crosses from one detection zone to the next, just as we only have a transponder in the middle of our train. With a deeper DoF the edges of the DoF may or may not be past the "Upper" and "Lower" focus distance, but we can't know that since only the position of the actual focus distance can be measured as anywhere between two of the detectors at various positions between minimum focus distance and infinity.



            The camera only reports the range of the actual focus distance, the focal length, and the aperture used. EXIF Info makes an educated guess at the DoF based on combining those three factors.



            In the end, DoF calculations are only estimates. Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel-peeping.






            share|improve this answer

























            • This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

              – juhist
              yesterday













            1












            1








            1







            Imagine a train track with detectors every 2 miles that will detect the presence of a train. Also imagine that we have a transponder placed near the middle of the train that triggers the detectors when it passes.



            If a very short express train less than a quarter mile in length has passed mile 6 but has not yet reached mile 8, the best that the system can tell anyone is that the train is somewhere between mile 6 and mile 8.



            Now consider that we have a very long, heavy freight train that is three miles long. At times our three mile long train will be next to two detectors, with the transponder in between. At other times, when the transponder is within one-half mile of a detector, the train will only be next to one detector. When the transponder is between detectors, we still won't know exactly where the head end of the train is.



            Basically, the sensors in the lens that report distance information to the camera are like the detectors every two miles along our train track. They tell the camera what positions the lens is focused between. The "Focus Distance Lower" is the closest position the lens might currently be focused at. The "Focus Distance Upper" is the furthest position the lens might currently be focused. The lens might actually be focussed anywhere within that range.




            Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?




            The depth of field is like the length of our train. With a wide aperture, we have a short express train. With a narrow aperture, we have a long freight train. We only can sense when the focus distance in the middle of the DoF crosses from one detection zone to the next, just as we only have a transponder in the middle of our train. With a deeper DoF the edges of the DoF may or may not be past the "Upper" and "Lower" focus distance, but we can't know that since only the position of the actual focus distance can be measured as anywhere between two of the detectors at various positions between minimum focus distance and infinity.



            The camera only reports the range of the actual focus distance, the focal length, and the aperture used. EXIF Info makes an educated guess at the DoF based on combining those three factors.



            In the end, DoF calculations are only estimates. Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel-peeping.






            share|improve this answer















            Imagine a train track with detectors every 2 miles that will detect the presence of a train. Also imagine that we have a transponder placed near the middle of the train that triggers the detectors when it passes.



            If a very short express train less than a quarter mile in length has passed mile 6 but has not yet reached mile 8, the best that the system can tell anyone is that the train is somewhere between mile 6 and mile 8.



            Now consider that we have a very long, heavy freight train that is three miles long. At times our three mile long train will be next to two detectors, with the transponder in between. At other times, when the transponder is within one-half mile of a detector, the train will only be next to one detector. When the transponder is between detectors, we still won't know exactly where the head end of the train is.



            Basically, the sensors in the lens that report distance information to the camera are like the detectors every two miles along our train track. They tell the camera what positions the lens is focused between. The "Focus Distance Lower" is the closest position the lens might currently be focused at. The "Focus Distance Upper" is the furthest position the lens might currently be focused. The lens might actually be focussed anywhere within that range.




            Why in one of the pictures (shallow DoF) is the difference between focus distances higher than the DoF, and in the other picture (deep DoF) is the difference between focus distances lower than the DoF?




            The depth of field is like the length of our train. With a wide aperture, we have a short express train. With a narrow aperture, we have a long freight train. We only can sense when the focus distance in the middle of the DoF crosses from one detection zone to the next, just as we only have a transponder in the middle of our train. With a deeper DoF the edges of the DoF may or may not be past the "Upper" and "Lower" focus distance, but we can't know that since only the position of the actual focus distance can be measured as anywhere between two of the detectors at various positions between minimum focus distance and infinity.



            The camera only reports the range of the actual focus distance, the focal length, and the aperture used. EXIF Info makes an educated guess at the DoF based on combining those three factors.



            In the end, DoF calculations are only estimates. Since depth of field will change for different display sizes of the exact same image, any camera estimate of DoF is only a guess based upon an assumption of the intended display size. The long standing assumed "standard" is an 8x10 image viewed at a distance of 12 inches by a person with 20/20 vision. But in the digital age that goes out the window very quickly when pixel-peeping.







            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited 11 hours ago

























            answered 2 days ago









            Michael CMichael C

            133k7152378




            133k7152378












            • This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

              – juhist
              yesterday

















            • This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

              – juhist
              yesterday
















            This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

            – juhist
            yesterday





            This seems to be a valid theory: I took four pictures of some grapes on a table with a 85mm f/1.8 lens, and two of them have 0.85-0.89 m focus, two have 0.89-1.05 m focus.

            – juhist
            yesterday

















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