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Thread: Does aperture affect the geometry of an image??

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    Does aperture affect the geometry of an image??

    Hello, my name is Kauê de Moraes Vestena, already introduced myself in this community here: NEW MEMBER? Please Introduce Yourself Here

    So, for months this question have intrigued myself. Before reading about the effects of aperture, i dit not know how it really changes the focus of every element in the image, and it have been a lot of surprise to me!

    I like photography a lot, but for the moment, i'm most interessed in use photographies to reconstruct 3D scenes, and i have been amazed how the photographic settings could affect the results. In my country most of researchers in the photogrammetry area had forgotten the importance of the photography and even of the optics, and it's really creepy.

    In my university, i fear that i'm really helpless. So i came here to make that question.

    The point is: for photogrammetric goals, the most interesting effects to be corrected are the barrel/pincushion distortion or every effect (mainly distortions at all) that causes any displacement (yep, that is the keyword: displacement) with respect to the ideal (pinhole) model. Any radiometric effect is also important, but more for digital processing, and automatic extraction of infos.

    And i've questioned myself: does the aperture modifies the geometry that create the image as it is?? It could affect the accutance as i'd read in the site, so i'm wondered that it locally could affect the correct definition of any element, but it could cause any generalized displacement, as barrel distortion does?

    If it could be a little off the scope of that forum, I hope that we could discuss it together, and I want to help too if I can. And again, sorry for my beginner english.

    Thank you a lot, since now!
    Best regards,
    Kauê

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    Moderator Dave Humphries's Avatar
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    re: Does aperture affect the geometry of an image??

    Hi Kauê,

    Welcome to the CiC forums from me.

    Photogrammetry, which I had to look up on Wikipedia, is certainly not our usual area of expertise.

    If you're looking for extreme measurement accuracy, the first thought that crosses my mind is that if you capture an image with broad spectrum light, you are at the mercy of the different colours of light being focussed in different places on the sensor plane, this is known as Chromatic Aberration (CA), both lateral and axial - which (I'm sure) will be affected by the choice of aperture. As will Depth of Field; the areas of sharpest resolution, dependent upon subject distance vs focus distance and aperture. However, I'm sure you probably knew all this.

    I guess this is why LiDAR (laser based) scanners are chosen for use on robots, self-drive cars and crime scene logging equipment, operating at one specific wavelength of light and avoiding all those CA issues.

    And i've questioned myself: does the aperture modifies the geometry that create the image as it is?? It could affect the accutance as i'd read in the site, so i'm wondered that it locally could affect the correct definition of any element, but it could cause any generalized displacement, as barrel distortion does?
    However, if you interest is in subject areas requiring less accuracy and/or where laser illumination is not possible; for example aerial/satellite surveillance, then yes, it might well apply, because of CA (rather than barrel distortion).

    Hope that helps, Dave

    PS we have a few members who might be able to help, let's see if they respond.
    I have slightly modified the thread title to make it more effective (I hope)

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    William W's Avatar
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    Re: Does aperture affect the geometry of an image??

    Quote Originally Posted by kauevestena View Post
    . . . for photogrammetric goals, the most interesting effects to be corrected are the barrel/pincushion distortion or every effect . . . that causes any displacement . . . with respect to the ideal (pinhole) model . . . And i've questioned myself: does the aperture modifies the geometry that create the image as it is? . . .
    Good exam question.

    The size of the Aperture does not affect the severity of Barrel or Pincushion Distortion.

    The size of the Aperture will affect the severity the Curvature of Field. Stopping down the Aperture (smaller Aperture) will bring into sharper focus those points on the Subject which were out of focus due to Curvature of Field.

    However: if the Out of Focus point on the Subject remains stationary, although that point will be brought into sharper focus when the lens is stopped down, the rendition of that point will not move its position on the Film/Sensor Plane.

    This relationship was shown by Ernst Karl Abbe when he experimented with what he named “the principle ray”. This is the ray which passes through the centre of the entrance pupil.

    Abbe showed that it is only this ‘principle ray’ which requires consideration for the rectilinear correctness, or degree of incorrectness (i.e. Barrel or Pincushion) of the image. Hence, a change in Aperture has nil effect in regard to Barrel and Pincushion Distortion.

    WW

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    Re: Does aperture affect the geometry of an image??

    Dave alerted me of your query and I immediately knew what text to draw upon to help you out.

    The explanation and illustration below come from the "Photographer's Mate 2 & 3", Bureau of Naval Personnel, Rate Training Manual, NAVPERS 10355-A, 1971 Edition. This was my first introduction to photography when attending high/middle school and it is still my primary reference.

    Curvilinear distortion in a lens causes straight lines in the subject to be reproduced as curved lines in the image. When curvilinear distortion is present in a lens, it is particularly prominent in that portion of the image formed near the margins of the field of the lens. Hence, curvilinear distortion may be defined as a lens' inability to produce the same enlargement in the image formed by the edges of the lens as in that part formed by the center of the lens.

    When considering the case of a simple, single element, lens, uncorrected for spherical aberration, it will form an undistorted image. However, if an aperture or stop is placed on the optical axis to reduce spherical aberration, curvilinear distortion is the result. When the aperture or stop is placed in front of the lens, on the side facing the scene, negative distortion manifests itself by causing straight lines in the subject to appear bowed outward in the image, Barrel distortion, see (A) below. If the aperture or stop is placed behind the lens positive distortion manifests itself by causing the subject's straight lines to curve inward toward the center of the image, Pincushion distortion, see (B) below.

    Does aperture affect the geometry of an image??
    This is a photo "Scan" of the book illustration which is why there are introduced distortions,
    But you can see where curvilinear distortions originate.

    The obvious correction for curvilinear distortion is a multi-element lens which has the aperture and spherical aberration stops placed between lens elements.

    Since curvilinear distortion is greatest at the margins of the image circle, one easy method to mitigate the effect is to use a lens with a larger image circle or crop the image to the center region of the frame, in both instances, curvilinear distortion is aperture independent.

    If you need a mathematical basis for understanding and possibly compensating for curvilinear distortion, I recommend Lens Design Fundamentals by Rudolf Kingslake & R. Barry Johnson, specifically Chapter 11.

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    Moderator Manfred M's Avatar
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    Re: Does aperture affect the geometry of an image??

    Many forms of distortion are quite easy to correct in the digital editing process. Lens profiles that account for drop-off, distortion and spherochromatism are often corrected in-camera when shooting jpeg or when using raw converters like Adobe Camera Raw or DxO Labs Optics Pro.

    It is reasonably simple to create these profiles in some tools for lenses where there are no published profiles.

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    Re: Does aperture affect the geometry of an image??

    Thanks for the link Steaphany: very interesting. I answered from my knowledge of the history of (camera) lens development, the History of Photography - those navy training manuals seem to have a passionate technical basis explaining from the first principles, what a store of gold to have in your library!

    Thanks again,

    WW

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    Re: Does aperture affect the geometry of an image??

    Quote Originally Posted by Steaphany View Post
    Dave alerted me of your query and I immediately knew what text to draw upon to help you out.

    The explanation and illustration below come from the "Photographer's Mate 2 & 3", Bureau of Naval Personnel, Rate Training Manual, NAVPERS 10355-A, 1971 Edition. This was my first introduction to photography when attending high/middle school and it is still my primary reference.

    Curvilinear distortion in a lens causes straight lines in the subject to be reproduced as curved lines in the image. When curvilinear distortion is present in a lens, it is particularly prominent in that portion of the image formed near the margins of the field of the lens. Hence, curvilinear distortion may be defined as a lens' inability to produce the same enlargement in the image formed by the edges of the lens as in that part formed by the center of the lens.

    When considering the case of a simple, single element, lens, uncorrected for spherical aberration, it will form an undistorted image. However, if an aperture or stop is placed on the optical axis to reduce spherical aberration, curvilinear distortion is the result. When the aperture or stop is placed in front of the lens, on the side facing the scene, negative distortion manifests itself by causing straight lines in the subject to appear bowed outward in the image, Barrel distortion, see (A) below. If the aperture or stop is placed behind the lens positive distortion manifests itself by causing the subject's straight lines to curve inward toward the center of the image, Pincushion distortion, see (B) below.

    Does aperture affect the geometry of an image??
    This is a photo "Scan" of the book illustration which is why there are introduced distortions,
    But you can see where curvilinear distortions originate.

    The obvious correction for curvilinear distortion is a multi-element lens which has the aperture and spherical aberration stops placed between lens elements.

    Since curvilinear distortion is greatest at the margins of the image circle, one easy method to mitigate the effect is to use a lens with a larger image circle or crop the image to the center region of the frame, in both instances, curvilinear distortion is aperture independent.

    If you need a mathematical basis for understanding and possibly compensating for curvilinear distortion, I recommend Lens Design Fundamentals by Rudolf Kingslake & R. Barry Johnson, specifically Chapter 11.
    Interesting. Is this due to diffraction?

    George

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    Re: Does aperture affect the geometry of an image??

    Who am I to argue with the American Navy . . .? But I am very skeptical about the explanation in the extract quoted by Steaphany.

    If the image is in focus, any ray from a point of the object hits the sensor/film in the same place. If the diaphragm is inserted to block off some of the rays, wherever it is inserted, the rays that get through should still hit the sensor in the same place and should not affect the distortion.

    I don't understand the statement "a simple lens UNcorrected for spherical aberration will form an UNdistorted image". There seem to be too many UNs in this sentence.

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    Re: Does aperture affect the geometry of an image??

    Quote Originally Posted by TonyW View Post
    I don't understand the statement "a simple lens UNcorrected for spherical aberration will form an UNdistorted image". There seem to be too many UNs in this sentence.
    Sorry for the awkward wording, The description was a consolidation of the text from the naval training manual, which often uses language in a somewhat dated fashion.

    A point to keep in mind is that further research into factors that contribute and cause curvilinear distortions are either non-existent or explained by means of mathematical formulas intended for optical system analysis and characterization for optical design. For the field of photography, it pretty much amounts to what pincushion and barrel distortions do to images, an example of what is available is Introduction to Aberrations, and often contrasted by methods to fix or compensate in lightroom or photoshop. The naval training manual is my only source that provides a geometrical explanation of the origins of curvilinear distortions.

    One of the better published papers on the subject comes from Zeiss, Distortion by B. Hönlinger and H. H. Nasse which still addresses a photographic lens system as a black box exhibiting a resultant quantifiable performance.

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    Re: Does aperture affect the geometry of an image??

    Quote Originally Posted by Steaphany View Post
    The explanation and illustration below come from the "Photographer's Mate 2 & 3", Bureau of Naval Personnel, Rate Training Manual, NAVPERS 10355-A, 1971 Edition. This was my first introduction to photography when attending high/middle school and it is still my primary reference.

    Curvilinear distortion in a lens causes straight lines in the subject to be reproduced as curved lines in the image. When curvilinear distortion is present in a lens, it is particularly prominent in that portion of the image formed near the margins of the field of the lens. Hence, curvilinear distortion may be defined as a lens' inability to produce the same enlargement in the image formed by the edges of the lens as in that part formed by the center of the lens.

    When considering the case of a simple, single element, lens, uncorrected for spherical aberration, it will form an undistorted image. However, if an aperture or stop is placed on the optical axis to reduce spherical aberration, curvilinear distortion is the result. When the aperture or stop is placed in front of the lens, on the side facing the scene, negative distortion manifests itself by causing straight lines in the subject to appear bowed outward in the image, Barrel distortion, see (A) below. If the aperture or stop is placed behind the lens positive distortion manifests itself by causing the subject's straight lines to curve inward toward the center of the image, Pincushion distortion, see (B) below.

    Does aperture affect the geometry of an image??
    This is a photo "Scan" of the book illustration which is why there are introduced distortions,
    But you can see where curvilinear distortions originate.

    The obvious correction for curvilinear distortion is a multi-element lens which has the aperture and spherical aberration stops placed between lens elements.

    Since curvilinear distortion is greatest at the margins of the image circle, one easy method to mitigate the effect is to use a lens with a larger image circle or crop the image to the center region of the frame, in both instances, curvilinear distortion is aperture independent.

    If you need a mathematical basis for understanding and possibly compensating for curvilinear distortion, I recommend Lens Design Fundamentals by Rudolf Kingslake & R. Barry Johnson, specifically Chapter 11.
    Steaphany, does that illustration assume a circular aperture? In other words, if the aperture were to be rectangular with the same aspect ratio and orientation as the 'F' would there still be distortion?

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    Steaphany's Avatar
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    Re: Does aperture affect the geometry of an image??

    Quote Originally Posted by xpatUSA View Post
    Steaphany, does that illustration assume a circular aperture? In other words, if the aperture were to be rectangular with the same aspect ratio and orientation as the 'F' would there still be distortion?
    Yes, the distortion is not effected by the aperture geometry, remember that the cause of curvilinear distortion is a variation in focal length of the lens between light passing through the center versus light that through the periphery.

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    Re: Does aperture affect the geometry of an image??

    WOW!!
    Thanks all of you for that amazing answers, above all, for that:

    Quote Originally Posted by Steaphany View Post
    One of the better published papers on the subject comes from Zeiss, Distortion by B. Hönlinger and H. H. Nasse which still addresses a photographic lens system as a black box exhibiting a resultant quantifiable performance.
    What's an amazing paper!!!

    So, following the answers order:

    Thanks for the welcome, Dave.
    Lidar and classic photogrammetric techniques are complementar, and also, LiDAR is much more expensive, and i'm really loving study photographic cameras geometry and all its particularities.

    The CA seems to be the most troubling effect, but i can use olny the info of green band to reduce its effects (just if it occurs).

    William W, thanks for the contribution. After make the post, and read all the answers, i think i've realized whats the point: maybe the aperture do not cause displacements, but it can bring elements in image out of focus, and it could be a trouble for the identification of any individual element like a countour of a circunference, because in photogrammetry it's all (at the most) about that: identify features in images. And a blurried feature, could cause errouneous interpretation of the correct position, if it be done by a human or also by an algorithym. Like what occur in that image: https://upload.wikimedia.org/wikiped...parison%29.jpg

    Stheaphany, thanks a lot!

    But these statement:
    Quote Originally Posted by Steaphany View Post
    if an aperture or stop is placed on the optical axis to reduce spherical aberration, curvilinear distortion is the result.
    seems to be a little contradictory with that (and with all the rest of the thread ideas, and with my knowledge)

    Quote Originally Posted by Steaphany View Post
    ...curvilinear distortion is aperture independent.
    How it can be the result, if they are independent? I'm so interessted in that idea: the position of the stop in relation of the lenses (horizontally, expanding the focal distance) could change the distortion, behavior!!!

    Quote Originally Posted by Steaphany View Post
    A point to keep in mind is that further research into factors that contribute and cause curvilinear distortions are either non-existent or explained by means of mathematical formulas intended for optical system analysis and characterization for optical design.
    (again) I really liked the links, do you have more of that (links or knowledgs of that effects)? In my area, are these two papers:
    https://eserv.asprs.org/PERS/1966jou...ay_444-462.pdf
    http://www.isprs.org/proceedings/xxv...XXVI-part5.pdf

    And others, by Duane Brown and/or J. G. Fryer and various authors


    Again, thank you all!!

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    Re: Does aperture affect the geometry of an image??

    I had a quick look at the Zeiss reference quoted by Steaphany. I question some of the statements there but they do say "And distortion is not changed by stopping down", which implies to me that the answer to the original question is that aperture does not affect the geometry of the image.

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