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Can you tell from a blurry photo if focus was too close or too far?


How close can a lens focus?How can I repair missed focus in a valuable photo?How can I fix an out-of-focus blurred photo in Photoshop?I'm having trouble getting sharp pictures while shooting a concert from a press pass locationNikon D3000 Blurry Pictures. Focus Issue?does depth of field travel with the focal plane?Why can lenses only focus from so close?Why do I get blurry pictures at far distances, but sharp results up close?Why isn't this portrait taken at f/29 sharp?Can you determine if focus is sharp without diopter adjustment if your sight is imperfect?













8















If you focus for a plane that is too much in front of your subject, or too far past it (relative to depth of field) then the subject will appear blurry. Is there some way of telling purely from the resulting picture if focus was too near or too far?



EDIT: to clarify, I don't mean plane as in airplane, I meant the "plane" in space that is, for a given focus setting, sharp. As determined by the lens and film/sensor. The focal plane. The question comes down to "can you detect from blur whether it was back-focus or front-focus?"










share|improve this question




















  • 2





    panasonic says they can imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM

    – szulat
    6 hours ago
















8















If you focus for a plane that is too much in front of your subject, or too far past it (relative to depth of field) then the subject will appear blurry. Is there some way of telling purely from the resulting picture if focus was too near or too far?



EDIT: to clarify, I don't mean plane as in airplane, I meant the "plane" in space that is, for a given focus setting, sharp. As determined by the lens and film/sensor. The focal plane. The question comes down to "can you detect from blur whether it was back-focus or front-focus?"










share|improve this question




















  • 2





    panasonic says they can imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM

    – szulat
    6 hours ago














8












8








8








If you focus for a plane that is too much in front of your subject, or too far past it (relative to depth of field) then the subject will appear blurry. Is there some way of telling purely from the resulting picture if focus was too near or too far?



EDIT: to clarify, I don't mean plane as in airplane, I meant the "plane" in space that is, for a given focus setting, sharp. As determined by the lens and film/sensor. The focal plane. The question comes down to "can you detect from blur whether it was back-focus or front-focus?"










share|improve this question
















If you focus for a plane that is too much in front of your subject, or too far past it (relative to depth of field) then the subject will appear blurry. Is there some way of telling purely from the resulting picture if focus was too near or too far?



EDIT: to clarify, I don't mean plane as in airplane, I meant the "plane" in space that is, for a given focus setting, sharp. As determined by the lens and film/sensor. The focal plane. The question comes down to "can you detect from blur whether it was back-focus or front-focus?"







focus blur focus-distance






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 6 hours ago







G_H

















asked 8 hours ago









G_HG_H

2507




2507








  • 2





    panasonic says they can imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM

    – szulat
    6 hours ago














  • 2





    panasonic says they can imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM

    – szulat
    6 hours ago








2




2





panasonic says they can imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM

– szulat
6 hours ago





panasonic says they can imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM

– szulat
6 hours ago










5 Answers
5






active

oldest

votes


















3














It depends. In many cases, it may actually be possible without any further visual aids in the picture.



Many lenses, if not most, will show different longitudinal chromatic aberration in front of and behind the focus plane. If you scroll down just a little bit on the linked page, you will see this demonstrated with a picture of a focus test chart. With this lens, the blur in front of the focus point will have purple colour fringing, while the blur behind the focus point will seem greenish.



If you know the characteristics of this lens, you could look at just a very small part of the image like e.g:



enter image description here



... and say for sure that this out-of-focus area is behind the focus plane.






share|improve this answer



















  • 2





    so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

    – ths
    41 mins ago





















2














If the plane is too far or to close is just from the blur hard to say. the easiest way is to have objects in front and behind and see which one is sharp and so you could determine if it is too far or too close... this is the same way as it is done by calibrating the autofocus of a lens with a lenscal tool like this.



without such objects its hard to tell it.






share|improve this answer































    1














    My answer only deals with "human" ways in differentiation - that is: No software, only your eyes and hands.



    If I have no reference (as in: you blind me, you set the focus distance, and then I can only look through the viewfinder, but cannot change a thing), the answer is: it depends on what I can see.



    Take, for example, an alley of trees: one in front, one where the subject stands, and one in the distance. When I see that the subject is not sharp, I can try to tell whether the tree in the foreground or the one in the background is more in focus.



    If I have no reference - e.g., as Yaba mentioned, when taking a photo of a aeroplane with blue sky in the background and no foreground, then I have no way to know exactly (my guess would be that focus is too close, however, as planes tend to be somewhere near infinity).





    The easiest way to find out usually is to slightly change the focus and see where it is (again, this works better with a reference than without).



    But generally speaking, there is no sure way to differentiate - too short a focus distance does not lead to (significantly) different blur compared to a focus distance that is too long.






    share|improve this answer































      0














      With a plane in the sky it get's hard. Unlike there are other objects at different distances available (Birds, Clouds,...) you cannot compare it easily visually.



      Some lense/camera combinations can track the focus distance and will write it into the EXIFs. However this is not very reliable, but could give you a hint. When you know the plane type and therefore can look up it's real size you can calculate it's aproximate distance and compare this to the focus distance.



      This page with its calculator can help you with this: https://www.scantips.com/lights/subjectdistance.html






      share|improve this answer



















      • 3





        Geometric plane not Aeroplane

        – Tetsujin
        7 hours ago











      • Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

        – Yaba
        6 hours ago






      • 2





        @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

        – G_H
        6 hours ago











      • @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

        – G_H
        4 hours ago



















      0














      No



      it is technically not possible to detect from the blur alone how far or in which direction the image is out of focus.



      This is the reason why contrast-detection autofocus systems have to "hunt" for focus by repeatedly changing the focus distance and checking whether the image got better or worse.



      In contrast, phase-detection AF systems know (theoretically) exactly how far and in which direction they have to change focus to achieve optimal sharpness.



      Of course the image changes if you take context clues from other objects in the picture into account (i.e. "guessing"), but that is something which currently ony organic viewers can do. This might change with AI algorithms in-camera, but i suspect other advances will improve on pure CD-AF before that. (see @szulat 's link from acomment:https://www.imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM)






      share|improve this answer
























      • In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

        – rackandboneman
        1 hour ago











      Your Answer








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      5 Answers
      5






      active

      oldest

      votes








      5 Answers
      5






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      3














      It depends. In many cases, it may actually be possible without any further visual aids in the picture.



      Many lenses, if not most, will show different longitudinal chromatic aberration in front of and behind the focus plane. If you scroll down just a little bit on the linked page, you will see this demonstrated with a picture of a focus test chart. With this lens, the blur in front of the focus point will have purple colour fringing, while the blur behind the focus point will seem greenish.



      If you know the characteristics of this lens, you could look at just a very small part of the image like e.g:



      enter image description here



      ... and say for sure that this out-of-focus area is behind the focus plane.






      share|improve this answer



















      • 2





        so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

        – ths
        41 mins ago


















      3














      It depends. In many cases, it may actually be possible without any further visual aids in the picture.



      Many lenses, if not most, will show different longitudinal chromatic aberration in front of and behind the focus plane. If you scroll down just a little bit on the linked page, you will see this demonstrated with a picture of a focus test chart. With this lens, the blur in front of the focus point will have purple colour fringing, while the blur behind the focus point will seem greenish.



      If you know the characteristics of this lens, you could look at just a very small part of the image like e.g:



      enter image description here



      ... and say for sure that this out-of-focus area is behind the focus plane.






      share|improve this answer



















      • 2





        so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

        – ths
        41 mins ago
















      3












      3








      3







      It depends. In many cases, it may actually be possible without any further visual aids in the picture.



      Many lenses, if not most, will show different longitudinal chromatic aberration in front of and behind the focus plane. If you scroll down just a little bit on the linked page, you will see this demonstrated with a picture of a focus test chart. With this lens, the blur in front of the focus point will have purple colour fringing, while the blur behind the focus point will seem greenish.



      If you know the characteristics of this lens, you could look at just a very small part of the image like e.g:



      enter image description here



      ... and say for sure that this out-of-focus area is behind the focus plane.






      share|improve this answer













      It depends. In many cases, it may actually be possible without any further visual aids in the picture.



      Many lenses, if not most, will show different longitudinal chromatic aberration in front of and behind the focus plane. If you scroll down just a little bit on the linked page, you will see this demonstrated with a picture of a focus test chart. With this lens, the blur in front of the focus point will have purple colour fringing, while the blur behind the focus point will seem greenish.



      If you know the characteristics of this lens, you could look at just a very small part of the image like e.g:



      enter image description here



      ... and say for sure that this out-of-focus area is behind the focus plane.







      share|improve this answer












      share|improve this answer



      share|improve this answer










      answered 1 hour ago









      jarnbjojarnbjo

      1,36369




      1,36369








      • 2





        so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

        – ths
        41 mins ago
















      • 2





        so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

        – ths
        41 mins ago










      2




      2





      so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

      – ths
      41 mins ago







      so, you can't determine it from the blur (which this question is asking about). you need additional information about the lens and other abberations.

      – ths
      41 mins ago















      2














      If the plane is too far or to close is just from the blur hard to say. the easiest way is to have objects in front and behind and see which one is sharp and so you could determine if it is too far or too close... this is the same way as it is done by calibrating the autofocus of a lens with a lenscal tool like this.



      without such objects its hard to tell it.






      share|improve this answer




























        2














        If the plane is too far or to close is just from the blur hard to say. the easiest way is to have objects in front and behind and see which one is sharp and so you could determine if it is too far or too close... this is the same way as it is done by calibrating the autofocus of a lens with a lenscal tool like this.



        without such objects its hard to tell it.






        share|improve this answer


























          2












          2








          2







          If the plane is too far or to close is just from the blur hard to say. the easiest way is to have objects in front and behind and see which one is sharp and so you could determine if it is too far or too close... this is the same way as it is done by calibrating the autofocus of a lens with a lenscal tool like this.



          without such objects its hard to tell it.






          share|improve this answer













          If the plane is too far or to close is just from the blur hard to say. the easiest way is to have objects in front and behind and see which one is sharp and so you could determine if it is too far or too close... this is the same way as it is done by calibrating the autofocus of a lens with a lenscal tool like this.



          without such objects its hard to tell it.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 3 hours ago









          LuZelLuZel

          501216




          501216























              1














              My answer only deals with "human" ways in differentiation - that is: No software, only your eyes and hands.



              If I have no reference (as in: you blind me, you set the focus distance, and then I can only look through the viewfinder, but cannot change a thing), the answer is: it depends on what I can see.



              Take, for example, an alley of trees: one in front, one where the subject stands, and one in the distance. When I see that the subject is not sharp, I can try to tell whether the tree in the foreground or the one in the background is more in focus.



              If I have no reference - e.g., as Yaba mentioned, when taking a photo of a aeroplane with blue sky in the background and no foreground, then I have no way to know exactly (my guess would be that focus is too close, however, as planes tend to be somewhere near infinity).





              The easiest way to find out usually is to slightly change the focus and see where it is (again, this works better with a reference than without).



              But generally speaking, there is no sure way to differentiate - too short a focus distance does not lead to (significantly) different blur compared to a focus distance that is too long.






              share|improve this answer




























                1














                My answer only deals with "human" ways in differentiation - that is: No software, only your eyes and hands.



                If I have no reference (as in: you blind me, you set the focus distance, and then I can only look through the viewfinder, but cannot change a thing), the answer is: it depends on what I can see.



                Take, for example, an alley of trees: one in front, one where the subject stands, and one in the distance. When I see that the subject is not sharp, I can try to tell whether the tree in the foreground or the one in the background is more in focus.



                If I have no reference - e.g., as Yaba mentioned, when taking a photo of a aeroplane with blue sky in the background and no foreground, then I have no way to know exactly (my guess would be that focus is too close, however, as planes tend to be somewhere near infinity).





                The easiest way to find out usually is to slightly change the focus and see where it is (again, this works better with a reference than without).



                But generally speaking, there is no sure way to differentiate - too short a focus distance does not lead to (significantly) different blur compared to a focus distance that is too long.






                share|improve this answer


























                  1












                  1








                  1







                  My answer only deals with "human" ways in differentiation - that is: No software, only your eyes and hands.



                  If I have no reference (as in: you blind me, you set the focus distance, and then I can only look through the viewfinder, but cannot change a thing), the answer is: it depends on what I can see.



                  Take, for example, an alley of trees: one in front, one where the subject stands, and one in the distance. When I see that the subject is not sharp, I can try to tell whether the tree in the foreground or the one in the background is more in focus.



                  If I have no reference - e.g., as Yaba mentioned, when taking a photo of a aeroplane with blue sky in the background and no foreground, then I have no way to know exactly (my guess would be that focus is too close, however, as planes tend to be somewhere near infinity).





                  The easiest way to find out usually is to slightly change the focus and see where it is (again, this works better with a reference than without).



                  But generally speaking, there is no sure way to differentiate - too short a focus distance does not lead to (significantly) different blur compared to a focus distance that is too long.






                  share|improve this answer













                  My answer only deals with "human" ways in differentiation - that is: No software, only your eyes and hands.



                  If I have no reference (as in: you blind me, you set the focus distance, and then I can only look through the viewfinder, but cannot change a thing), the answer is: it depends on what I can see.



                  Take, for example, an alley of trees: one in front, one where the subject stands, and one in the distance. When I see that the subject is not sharp, I can try to tell whether the tree in the foreground or the one in the background is more in focus.



                  If I have no reference - e.g., as Yaba mentioned, when taking a photo of a aeroplane with blue sky in the background and no foreground, then I have no way to know exactly (my guess would be that focus is too close, however, as planes tend to be somewhere near infinity).





                  The easiest way to find out usually is to slightly change the focus and see where it is (again, this works better with a reference than without).



                  But generally speaking, there is no sure way to differentiate - too short a focus distance does not lead to (significantly) different blur compared to a focus distance that is too long.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 3 hours ago









                  floliloliloflolilolilo

                  4,52911633




                  4,52911633























                      0














                      With a plane in the sky it get's hard. Unlike there are other objects at different distances available (Birds, Clouds,...) you cannot compare it easily visually.



                      Some lense/camera combinations can track the focus distance and will write it into the EXIFs. However this is not very reliable, but could give you a hint. When you know the plane type and therefore can look up it's real size you can calculate it's aproximate distance and compare this to the focus distance.



                      This page with its calculator can help you with this: https://www.scantips.com/lights/subjectdistance.html






                      share|improve this answer



















                      • 3





                        Geometric plane not Aeroplane

                        – Tetsujin
                        7 hours ago











                      • Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

                        – Yaba
                        6 hours ago






                      • 2





                        @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

                        – G_H
                        6 hours ago











                      • @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

                        – G_H
                        4 hours ago
















                      0














                      With a plane in the sky it get's hard. Unlike there are other objects at different distances available (Birds, Clouds,...) you cannot compare it easily visually.



                      Some lense/camera combinations can track the focus distance and will write it into the EXIFs. However this is not very reliable, but could give you a hint. When you know the plane type and therefore can look up it's real size you can calculate it's aproximate distance and compare this to the focus distance.



                      This page with its calculator can help you with this: https://www.scantips.com/lights/subjectdistance.html






                      share|improve this answer



















                      • 3





                        Geometric plane not Aeroplane

                        – Tetsujin
                        7 hours ago











                      • Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

                        – Yaba
                        6 hours ago






                      • 2





                        @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

                        – G_H
                        6 hours ago











                      • @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

                        – G_H
                        4 hours ago














                      0












                      0








                      0







                      With a plane in the sky it get's hard. Unlike there are other objects at different distances available (Birds, Clouds,...) you cannot compare it easily visually.



                      Some lense/camera combinations can track the focus distance and will write it into the EXIFs. However this is not very reliable, but could give you a hint. When you know the plane type and therefore can look up it's real size you can calculate it's aproximate distance and compare this to the focus distance.



                      This page with its calculator can help you with this: https://www.scantips.com/lights/subjectdistance.html






                      share|improve this answer













                      With a plane in the sky it get's hard. Unlike there are other objects at different distances available (Birds, Clouds,...) you cannot compare it easily visually.



                      Some lense/camera combinations can track the focus distance and will write it into the EXIFs. However this is not very reliable, but could give you a hint. When you know the plane type and therefore can look up it's real size you can calculate it's aproximate distance and compare this to the focus distance.



                      This page with its calculator can help you with this: https://www.scantips.com/lights/subjectdistance.html







                      share|improve this answer












                      share|improve this answer



                      share|improve this answer










                      answered 7 hours ago









                      YabaYaba

                      1373




                      1373








                      • 3





                        Geometric plane not Aeroplane

                        – Tetsujin
                        7 hours ago











                      • Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

                        – Yaba
                        6 hours ago






                      • 2





                        @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

                        – G_H
                        6 hours ago











                      • @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

                        – G_H
                        4 hours ago














                      • 3





                        Geometric plane not Aeroplane

                        – Tetsujin
                        7 hours ago











                      • Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

                        – Yaba
                        6 hours ago






                      • 2





                        @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

                        – G_H
                        6 hours ago











                      • @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

                        – G_H
                        4 hours ago








                      3




                      3





                      Geometric plane not Aeroplane

                      – Tetsujin
                      7 hours ago





                      Geometric plane not Aeroplane

                      – Tetsujin
                      7 hours ago













                      Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

                      – Yaba
                      6 hours ago





                      Well, then the question was not clear. In this case it's easy. Look for other elements either in the front or behind that are in focus. However if it that's what has been asked I wonder why it was asked as this is obvious, isn't it?

                      – Yaba
                      6 hours ago




                      2




                      2





                      @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

                      – G_H
                      6 hours ago





                      @Yaba "a plane that is too much in front of your subject". I think if an aeroplane is too close in front of what you're trying to shoot and in a state of movement that makes it hard to focus on, you have more urgent issues than getting a good photo.

                      – G_H
                      6 hours ago













                      @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

                      – G_H
                      4 hours ago





                      @Yaba The question is if there are aspects to the blurred part of an image that can tell you if it's a result of back-focus or front-focus. You may not have anything in front or back of the subject to tell. Back-focusing would put the intended image "behind" the film/sensor plane, front focusing in front of it. Meaning front-focusing also inverts it. I thought this might affect the appearance of the blur in some noticeable way. I'm asking out of interest.

                      – G_H
                      4 hours ago











                      0














                      No



                      it is technically not possible to detect from the blur alone how far or in which direction the image is out of focus.



                      This is the reason why contrast-detection autofocus systems have to "hunt" for focus by repeatedly changing the focus distance and checking whether the image got better or worse.



                      In contrast, phase-detection AF systems know (theoretically) exactly how far and in which direction they have to change focus to achieve optimal sharpness.



                      Of course the image changes if you take context clues from other objects in the picture into account (i.e. "guessing"), but that is something which currently ony organic viewers can do. This might change with AI algorithms in-camera, but i suspect other advances will improve on pure CD-AF before that. (see @szulat 's link from acomment:https://www.imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM)






                      share|improve this answer
























                      • In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

                        – rackandboneman
                        1 hour ago
















                      0














                      No



                      it is technically not possible to detect from the blur alone how far or in which direction the image is out of focus.



                      This is the reason why contrast-detection autofocus systems have to "hunt" for focus by repeatedly changing the focus distance and checking whether the image got better or worse.



                      In contrast, phase-detection AF systems know (theoretically) exactly how far and in which direction they have to change focus to achieve optimal sharpness.



                      Of course the image changes if you take context clues from other objects in the picture into account (i.e. "guessing"), but that is something which currently ony organic viewers can do. This might change with AI algorithms in-camera, but i suspect other advances will improve on pure CD-AF before that. (see @szulat 's link from acomment:https://www.imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM)






                      share|improve this answer
























                      • In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

                        – rackandboneman
                        1 hour ago














                      0












                      0








                      0







                      No



                      it is technically not possible to detect from the blur alone how far or in which direction the image is out of focus.



                      This is the reason why contrast-detection autofocus systems have to "hunt" for focus by repeatedly changing the focus distance and checking whether the image got better or worse.



                      In contrast, phase-detection AF systems know (theoretically) exactly how far and in which direction they have to change focus to achieve optimal sharpness.



                      Of course the image changes if you take context clues from other objects in the picture into account (i.e. "guessing"), but that is something which currently ony organic viewers can do. This might change with AI algorithms in-camera, but i suspect other advances will improve on pure CD-AF before that. (see @szulat 's link from acomment:https://www.imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM)






                      share|improve this answer













                      No



                      it is technically not possible to detect from the blur alone how far or in which direction the image is out of focus.



                      This is the reason why contrast-detection autofocus systems have to "hunt" for focus by repeatedly changing the focus distance and checking whether the image got better or worse.



                      In contrast, phase-detection AF systems know (theoretically) exactly how far and in which direction they have to change focus to achieve optimal sharpness.



                      Of course the image changes if you take context clues from other objects in the picture into account (i.e. "guessing"), but that is something which currently ony organic viewers can do. This might change with AI algorithms in-camera, but i suspect other advances will improve on pure CD-AF before that. (see @szulat 's link from acomment:https://www.imaging-resource.com/PRODS/panasonic-gh4/panasonic-gh4TECH.HTM)







                      share|improve this answer












                      share|improve this answer



                      share|improve this answer










                      answered 2 hours ago









                      thsths

                      5,3231620




                      5,3231620













                      • In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

                        – rackandboneman
                        1 hour ago



















                      • In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

                        – rackandboneman
                        1 hour ago

















                      In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

                      – rackandboneman
                      1 hour ago





                      In certain cases, software could determine this from other artifacts/aberrations that are a result of being out of focus - eg spherochromatism....

                      – rackandboneman
                      1 hour ago


















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