Optics in Photography

Kingslake, R.

doi:10.1117/3.43160

Cited by 108 publications

(83 citation statements)

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“…These effects are sometimes mistakenly thought to be the product of the focal length of the lens [6] -see [9] for a classic example. This is incorrect since narrow angle lenses (often termed 'telephoto lenses') possess the same view point (or perspective), as wider field lenses, even wide-angle lenses [1]. Focal length of the lens only determines the magnification or the amount of an image that falls in the field of view, not the perspective; so a large focal length will have a larger zoom at any given subject-to-camera distance [1][2][3]6].…”

Section: Introductionmentioning

confidence: 99%

“…At short subject-to-camera distances (SCD) it is well-known that the point projection of a 3D scene to a 2D plane in photography renders parts of objects closer to the lens of the camera larger than those positioned further away [1][2][3][4][5][6][7][8]. Point projection additionally causes false impressions of the true edges of 3D spherical objects, like a skull or a face, at short SCDs [1,3,4] (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Point projection additionally causes false impressions of the true edges of 3D spherical objects, like a skull or a face, at short SCDs [1,3,4] (Fig. 1 & 2).…”

Section: Introductionmentioning

confidence: 99%

“…If the subject is not positioned centrally in the field of view of the camera, then stretching of the object across the image plane can further add to the two aforementioned distortions [1] [4] ( Fig. 1 & 2).…”

Section: Introductionmentioning

confidence: 99%

“…If the view point (including the subject-to-camera distance) remains the same between images then changing the focal length of the lens has no impact on the recorded perspective [1][2][3]6].…”

Section: Introductionmentioning

confidence: 99%

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Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment

Stephan

2015

Forensic Science International

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The superimposition of a face photograph with that of a skull for identification purposes necessitates the use of comparable photographic parameters between the two image acquisition sessions, so that differences in optics and consequent recording of images does not thwart the morphological analysis. Widely divergent, but published, speculations about the thresholds at which perspective distortion becomes negligible (0.5 to >13.5 m) must be resolved and perspective distortion (PD) relationships quantified across their full range to judge tolerance levels, and the suitability of commonly employed contemporary equipment (e.g., 1 m photographic copy-stands). Herein, basic trigonometry is employed to map PD for two same sized 179 mm linear lengths -separated anteroposteriorly by 127 mm -as a function of subject-to-camera distance (SCD; 0.2 to 20 m). These lengths approximate basic craniofacial heights (e.g., tr-n) and widths (e.g., zy-zy), while the latter approximates facial depth (e.g., n-t). As anticipated, PD decayed in logarithmic and continuous manner with increasing SCD. At SCD of 12 m, the within-image PD was negligible (<1%). At <2.5 m SCD, it exceeded 5% and increased sharply as SCD decreased. Since life size images of skulls and faces are commonly employed for superimposition, a relative 1% perspective distortion difference is recommended as the ceiling standard for craniofacial comparison (translates into a ≤2 mm difference in physiognomical face height). Since superimposition depends on relative comparisons of a photographic pair (not one photograph), there is practically no scenario in superimposition casework where subject-to-camera distances should be ignored and no single distance at which PD should be considered negligible (even if one image holds >12 m subject-to-camera distance).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Point projection additionally causes false impressions of the true edges of 3D spherical objects, like a skull or a face, at short SCDs [1,3,4] (Fig. 1 & 2).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment

Stephan

2015

Forensic Science International

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Perceived Facial Distortions in Selfies Are Explained by Viewing Habits

Cooper

Banks

2018

JAMA Facial Plast Surg

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To the Editor In their recent article, Ward et al 1 analyze the effect of camera distance on the relative sizes of facial dimensions in photographs. They argue that these dimensions are distorted in "selfies"-photographs that people take of themselves with a smartphone camera at arm's length. Given the increasing popularity of selfies, they express concern that such photographs affect decisions about cosmetic medical procedures. We agree with the authors' calculations of facial dimensions in photographs. We wish, however, to clarify the cause of perceived nasal widening in selfies. The perceived nasal widening is not, as the authors suggest, due to physical distortion in the photographs. When you see a person's face from different distances, the image cast on your retinas changes, but the apparent 3-dimensional shape does not. Your brain takes into account the distance to the face and interprets the retinal images accordingly. What about when you look at photographs of faces, such as selfies? Every photograph of a face has a viewing distance from which the dimensions in the photograph (such as the nasal-bizygomatic ratio) faithfully reproduce the dimensions that the viewer would see when looking at the real 3-dimensional face from a specific distance. The trick is to find the correct viewing distance. With selfies, or any other photograph, you should view from a distance such that the visual angle subtended by the face in the photograph equals the angle that the face subtended from the camera's position when the photograph was taken. 2 For a selfie, this distance is going to be much closer than for a typical portrait, because the photograph was captured from close up. When you view from the correct distance, the perceived facial dimensions should closely match the true dimensions (assuming a high-quality lens is used, as in modern smartphone cameras). What happens if you view a photograph of a face from the wrong distance? When viewing from too close, the face appears compressed in depth and flatter than it actually is. When viewing from too far, the face appears stretched in depth and rounder than it is. 3,4 Importantly, these effects are not caused by distortions in the photographs but by a mismatch between the correct and actual viewing distances. The reader can try this out with the photographs in the article by Ward et al. 1 The correct distance for the selfie is very close: roughly twice the photograph's width. The correct distance for the other photograph is approximately 10 times the width. If you view the selfie from close up, it should look less distorted. Indeed, research suggests that people usually view photographs taken with short focal lengths-such as selfies-from much too great a distance. 4 This is the reason for the perceived distortion, and there is nothing inherently distorted in the photographs. Evaluations of perceived shape in photographs must take into consideration human perception and viewing habits, in addition to the physical properties of photographs.

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A liquid core waveguide fluorescence detector for multicapillary electrophoresis applied to DNA sequencing in a 91-capillary array

2000

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A new laser-induced fluorescence (LIF) detector for multicapillary electrophoresis is presented. The detection principle is based on waveguiding of the emitted fluorescence from the point of illumination to the capillary ends by total internal reflection (TIR) and imaging of the capillary ends. The capillaries themselves thus act as liquid core waveguides (LCWs). At the illumination point, the capillaries are arranged in a planar array, which allows clean and efficient illumination with a line-focused laser beam. The capillary ends are rearranged into a small, densely packed two-dimensional array, which is imaged end-on with high light collection efficiency and excellent image quality. Wavelength dispersion is obtained with a single prism. Intercapillary optical crosstalk is less than 0.5%, and rejection of stray light is very efficient. The detector is applied to four-color DNA sequencing by gel electrophoresis in a 91-capillary array, with simple fluorescein and rhodamine dyes as fluorophores. Since the imaged two-dimensional array is so compact, the detector has a high potential for very large-scale multiplexing.

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Optics in Photography

Cited by 108 publications

References 0 publications

Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment

Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment

Perceived Facial Distortions in Selfies Are Explained by Viewing Habits

A liquid core waveguide fluorescence detector for multicapillary electrophoresis applied to DNA sequencing in a 91-capillary array

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